Engineering ligand reactivity enables high-temperature operation of stable perovskite solar cells

Perovskite Solar Cells and Light Emitting Diodes: Materials Chemistry, Device Physics and Relationship

Solution-processed perovskite solar cells (PSCs) and perovskite light emitting diodes (PeLEDs) represent promising next-generation optoelectronic technologies. This Review summarizes recent advancements in the application of metal halide perovskite materials for PSC and PeLED devices to address the efficiency, stability and scalability issues. Emphasis is placed on material chemistry strategies used to control and engineer the composition, deposition process, interface and micro-nanostructure in solution-processed perovskite films, leading to high-quality crystalline thin films for optimal device performance. Furthermore, we retrospectively compare the device physics of PSCs and PeLEDs, their working principles and their energy loss mechanisms, examining the similarities and differences between the two types of devices. The reciprocity relationship suggests that a great PSC should also be a great PeLED, motivating the search for interconverting photoelectric bifunctional devices with maximum radiative recombination and negligible non-radiative recombination. Specific requirements of PSCs and PeLEDs in terms of bandgap, thickness, band alignment and charge transport to achieve this target are discussed in detail. Further challenges and issues are also illustrated, together with prospects for future development. Understanding these fundamentals, embracing recent breakthroughs and exploring future prospects pave the way toward the rational design and development of high-performance PSC and PeLED devices.

2D/3D Heterojunction Engineering for Hole Transport Layer-Free Carbon-Based Perovskite Solar Cells

Hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) own outstanding potential for commercial applications due to their attractive advantages of low cost and superior stability. However, the abundant defects and mismatched energy levels at the interface of the perovskite/carbon electrode severely limit the device efficiency and stability. Constructing a 2D layer on the surface of 3D perovskite films to form 2D/3D heterojunctions has been demonstrated to be an effective method of passivating surface defects and optimizing the energy level alignment in almost all kinds of PSCs. Due to the unique structure of HTL-free C-PSCs, 2D/3D heterojunctions play especially important roles. This review article summarizes the reports of 2D/3D perovskite heterojunctions in HTL-free C-PSCs. It describes the contributions of 2D/3D heterojunctions in terms of their roles in defect passivation, energy level optimization, and stability improvement. Finally, challenges and prospects of 2D/3D heterojunction for further development of HTL-free C-PSCs are highlighted.

Dissolvable molecular bridges promoting buried interface modification for high-performance inverted perovskite solar cells

Non-radiative recombination and suboptimal interfacial contact at the hole transportation layer (HTL)/perovskite interface critically suppress the device performance and stability of inverted perovskite solar cells (PSCs). Herein, we proposed a dissolvable molecular bridge (DMB) strategy by introducing 4-fluorobenzylphosphonic acid (4F-BPA) on the HTL for synergetic buried interface modification, aiming at both defect passivation and interfacial contact enhancement. Comprehensive characterizations and analyses revealed that approximately 80% of 4F-BPA on the HTL was dissolved into the perovskite precursor, promoting controlled crystallization through intermediate phase formation and predominantly accumulating at the HTL/perovskite interface, where it strongly coordinated with lead(II) cations to enhance the interfacial contact and align the energy levels. As a result, the champion device achieved a power conversion efficiency (PCE) of 25.10% with a fill factor of 84.23%. The unencapsulated devices (also without a UV filter) maintained 87.1% of their initial PCE after 1000 h of maximum power point tracking under 1 sun illumination (ISOS-L-1I) and retained 92.7% of their initial PCE after 1000 h in the dark storage test (ISOS-D-1). The DMB strategy establishes a universal and cost-efficient framework for buried interface engineering, unlocking new possibilities for large-area device fabrication and industrial-scale implementation.

Amidinium-Based 2D Spacer Cations Enhance Efficiency and High-Temperature Photostability of Perovskite Solar Cells

2D/3D perovskite heterojunctions represent a promising approach to enhance the efficiency and stability of perovskite solar cells (PSCs). However, the photostability at elevated temperatures of conventional 2D/3D heterostructures, employing ammonium-based spacer cations, is severely limited by deprotonation reactions, hindering their practical application. In this study, amidinium-based 2D spacer cations as an alternative, leveraging their higher acid dissociation constants, to mitigate deprotonation-induced instability while providing excellent defect passivation effect is introduced. Amidinium passivation not only facilitates formation of thermally stable 2D/3D heterostructures but also suppresses non-radiative recombination and enhances carrier transport dynamics. PSCs with amidinium-based bulk and surface passivation achieve a state-of-the-art power conversion efficiency of 26.52% for 2D/3D PSCs and exhibit outstanding high-temperature photostability, retaining 90.6% of initial efficiency after 1000 h of continuous illumination at maximum power point at 85 °C. This work offers valuable insights into designing high-performance, durable PSCs under challenging conditions.

Rationally tailored passivator with multisite surface-anchors for suppressing ion migration toward air-stable perovskite solar cells

Trap states in perovskite films fabricated using the solution method can capture photo-generated carriers, expedite ion migration, and contribute to decomposition of the perovskite layer, thereby emerging as a major threat to the commercialization of perovskite solar cells (PSCs). To address these issues, passivation of the surface traps on perovskite films via molecules with functional groups is proven to be one of the most effective tactics for obtaining high-performance PSCs. Herein, potassium nonafluoro-1-butanesulfonate (KNFBS) molecules with multiple chemical bonds, including multisite F atoms, sulfonic acid groups and K ions, were introduced as surface-anchoring passivators to improve the film quality and passivate trap states. Based on in situ conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) results, it was found that undercoordinated Pb and I vacancy defects on the surface and grain boundaries (GBs) of perovskite films can be synergistically curtailed via multiple chemical interactions, including Lewis acid-base, hydrogen and ionic bonds. Moreover, the influence of varied ligands on defects and halide ion migration in perovskites as well as the mechanism behind it were extensively explored. Therefore, the KNFBS-treated perovskite films with a more homogeneous surface potential distribution significantly reduced point and vacancy defects and dangling bond density, facilitated charge transfer, exhibited an optimized power conversion efficiency (PCE) of 20.88% and enhanced air stability for the PSCs fabricated and stored in fully open-air conditions. The work has not only elucidated the fundamental mechanisms of ion migration and multisite passivation at the surface and GBs of perovskites but also probes into ligand design strategies for further improving the performance of perovskite photovoltaics.

Mitigating Mobile-Ion-Induced Instabilities and Performance Losses in 2D Passivated Perovskite Solar Cells

Bulky ammonium salt-based passivation is an effective strategy for enhancing the performance and stability of perovskite solar cells (PSCs). Especially, phenethylammonium iodide (PEAI) is known to greatly improve open-circuit voltage (VOC) and fill factor (FF). Despite these benefits, PEAI passivation leads to substantial short-circuit current density (JSC) losses and rapid degradation under operational conditions. In this work, it is revealed that the JSC loss as well as the accelerated degradation in PEAI-passivated devices is caused by an increased mobile ion density. To mitigate this performance and stability-limiting mechanism, ultrathin layers of ammonium benzenesulfonate (ABS) and/or ethylenediammonium diiodide (EDAI2) salts are then introduced between the PEAI and the perovskite, which stabilize the 2D perovskite layer and impede diffusion even under upon prolonged illumination. This leads to a reduced mobile ion density both in fresh devices and in the long term, lowering losses JSC, and thus enables power conversion efficiencies of ≈25% with enhanced stability. Overall, this study not only addresses the limitations of PEAI-based 2D passivation but also paves the way for understanding 2D-induced ionic JSC losses.

Anion-Cation Synergistic Regulation of Low-Dimensional Perovskite Passivation Layer for Perovskite Solar Cells

Mixing 2D and 3D perovskite together is an effective strategy to enhance the stability of perovskite solar cells (PSCs). This strategy has been widely used in many recent works. Typically, 2D layer is formed by introducing 2D spacer onto 3D surfaces through in situ intercalation reaction. However, this intercalation may not stop after the 2D layer is formed. Progressive migration of 2D spacer into 3D bulk leads to increased n-values of 2D phases and deviation from optimized structural design. The high n-value 2D perovskite is less stable than the low n-value 2D perovskite and may be prone to degradation under external stresses. Here, a heteroatom ammonium ligand, thiomorpholine (SMOR) is found, which can effectively passivate the perovskite surface, and form a 1D phase or 2D phase depending on cation to anion ratio and the type of anions. Due to lower formation energy at 1:1 cation to anion ratio, 1D phase can prevent the formation of high-n-value 2D phase and show excellent thermal stability. The passivation of SMOR-based 1D perovskite boosts the device efficiency to 25.6% (certified 24.7%). More importantly, the unpackaged device can maintain >80% of its initial efficiency after stable operation at 85 °C for 1000 h.

Enhancing the Photovoltaic Performance of Directional-Growing Two-Dimensional Perovskites by Out-of-Plane Polarization

Two-dimensional (2D) perovskites have great application potential in the photovoltaic field, but the carriers can only be transmitted in-plane due to the limitation of the quantum well structure. It is usually necessary to induce a vertical orientation in photovoltaic devices to overcome this limitation. Here we find that the carrier limitation of 2D perovskites can be overcome by out-of-plane polarization. 4-(Aminomethyl)piperidiniumPbI4 (4-AMPI) is a low-band-gap 2D perovskite ferroelectric with out-of-plane polarization. In this work, 4-AMPI was annealed at different temperatures to fabricate photovoltaic devices growing along different crystal planes. Under the irradiation of AM 1.5G, the parallel-grown 4-AMPI films exhibit a photocurrent density comparable to that of vertically grown films, indicating that out-of-plane polarization can help carriers overcome quantum well constraints. Compared with the nonferroelectric 3-(aminomethyl)piperidiniumPbI4 (3-AMPI), the photocurrent density of 4-AMPI with out-of-plane polarization is significantly higher, which is attributed to the advantage of out-of-plane polarization for the generation and transport of carriers. This work suggests that 2D molecular ferroelectrics with out-of-plane polarization are potential candidates for the fabrication of photovoltaic devices.

C60-based ionic salt electron shuttle for high-performance inverted perovskite solar modules

Although C60 is usually the electron transport layer (ETL) in inverted perovskite solar cells, its molecular nature of C60 leads to weak interfaces that lead to non-ideal interfacial electronic and mechanical degradation. Here, we synthesized an ionic salt from C60, 4-(1',5'-dihydro-1'-methyl-2'H-[5,6] fullereno-C60-Ih-[1,9-c]pyrrol-2'-yl) phenylmethanaminium chloride (CPMAC), and used it as the electron shuttle in inverted PSCs. The CH2-NH3+ head group in the CPMA cation improved the ETL interface and the ionic nature enhanced the packing, leading to ~3-fold increase in the interfacial toughness compared to C60. Using CPMAC, we obtained ~26% power conversion efficiencies (PCEs) with ~2% degradation after 2,100 hours of 1-sun operation at 65°C. For minimodules (four subcells, 6 centimeters square), we achieved the PCE of ~23% with <9% degradation after 2,200 hours of operation at 55°C.

Iodoplumbate Complex Transformation for Efficient Perovskite Emitters

High-quality, low-defect perovskite emitters are crucial for achieving high-performance perovskite optoelectronics. Additive engineering, which involves incorporating organic molecules (predominately amino-based) into perovskite precursor solution, is an effective strategy for reducing perovskite defects and thereby achieving high-quality perovskite films. Many efforts have been made to identify suitable additives and to elucidate their roles in defect suppression. However, to date, the lowest trap density of 3D perovskite films is ≈1013 cm-3, which continues to constrain the enhancement of photoluminescence quantum efficiency (PLQE). Hence, unveiling the mechanisms of defect formation and further reducing trap-assisted nonradiative recombination, and consequently enhancing the PLQEs of 3D perovskite films, remains a significant challenge. Through in situ monitoring of the perovskite crystallization process, it is revealed that 3D perovskites retain numerous defects due to incomplete conversion of iodoplumbate complexes. The effectiveness of non-amino additives containing ester and ether groups is emphasized in promoting the complete conversion of iodoplumbate complexes prior to nucleation, thereby eliminating defect formation. As a result, high-quality 3D perovskites are obtained, exhibiting a trap density of 4.8 × 1012 cm-3 and a peak PLQE of 84.5%. Consequently, near-infrared perovskite light-emitting diodes with an impressive external quantum efficiency of 26.5% are realized.

Surface Engineering of Perovskite Solar Cells via the Dry-Vacuum Process: Deposition of Lead Halides and Alkylammonium Halides

Perovskite solar cells (PSCs) have demonstrated remarkably rapid efficiency improvements mainly through spin-coating-based solution processes. While these processes offer numerous advantages, there are also several limitations, prompting research into alternative fabrication methodologies for PSCs. Meanwhile, surface engineering has been identified as one of the most critical factors for enhancing the efficiency and stability of PSCs. For surface passivation, most studies reported to date, especially for n-i-p structures, have relied on solution-based processes. However, these solution processes face challenges in controlling the termination of perovskite surfaces, achieving fine thickness control, and dealing with lead halides that utilize common solvents with perovskites. In this study, we introduce a strategy employing a dry-vacuum deposition process to deposit PbI2 and PbCl2 with nanoscale thickness precision on perovskite thin films. This is followed by vacuum deposition of alkyl halides (4-methoxy-phenethylammonium-iodide, MeO-PEAI), which demonstrated improved photostability in devices compared to a typical solution-processed MeO-PEAI surface treatment.

Additive-Free Sequential Thermal Evaporation of Near-Intrinsic Pb-Sn Perovskites

To boost the efficiency of perovskite solar cells beyond the limit of a single-junction cell, tandem cells are employed, requiring low bandgap materials. This is realized by partially substituting lead(II) (Pb2+) with tin(II) (Sn2+) in the perovskite structure. In this work, a scalable method is presented to produce formamidinium lead tin iodide (FAPb0.5Sn0.5I3) films by sequential thermal evaporation (sTE) of PbSnI4, which is an alloy of SnI2 and PbI2, and FAI, in vacuum. Annealing at 200 °C yields a highly oriented and crystalline layer comprising grains over 1 µm on average. Photoconductance measurements reveal carrier lifetimes exceeding 2 µs and mobilities ≈100 cm2/(Vs). Structural analysis confirms that, while interdiffusion is abundant even at room temperature, the complete conversion requires high temperatures. Although the incorporation of Cs+ into the A-site of the perovskite increases the grain size, charge carrier dynamics are reduced. A comparison between the sTE films and spin-coated samples of the same composition demonstrates the superior photoconductance of the sTE films, without the need for any additives. Overall, this study showcases the potential of sTE for producing high-quality low band gap (LBG) perovskite materials.

1.5D Chiral Perovskites Mediated by Hydrogen-Bonding Network with Remarkable Spin-Polarized Property

In this study, we developed new chiral hybrid perovskites, (R/S-MBA)(GA)PbI4, by incorporating achiral guanidinium (GA+) and chiral R/S-methylbenzylammonium (R/S-MBA+) into the perovskite framework. The resulting materials possess a distinctive structural configuration, positioned between 1D and 2D perovskites, which we describe as 1.5D. This structure is featured by a hydrogen-bonding-network-induced arrangement of zigzag inorganic chains, further forming an organized layered architecture. The structural dimensionality affects both electronic and spin-related properties. Density functional theory (DFT) calculations reveal Rashba splitting induced by the inversion asymmetry of the crystal structure, while circularly polarized transient absorption spectroscopy confirms spin lifetime on the nanosecond timescale. Magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements demonstrate exceptional chiral-induced spin selectivity (CISS) with maximum spin polarization degrees of (92±1)% and (-94±2)% for (R-MBA)(GA)PbI4 and (S-MBA)(GA)PbI4, respectively. These findings underscore the potential of (R/S-MBA)(GA)PbI4 as promising candidates for next-generation spintronic devices, also highlight the critical role of chemical environment in sculpturing the structural dimension and spin-polarized property of chiral perovskites.

Fluoride Ion Passivation of CsPbBr3 Nanocrystals at Room Temperature for Highly Efficient and Stable White Light-Emitting Diodes

Inorganic halide perovskite nanocrystals (NCs) are regarded as promising emitters for light-emitting diodes due to their bright and narrow emission. However, surface defects often result in trap states and ion migration, which remains a huge challenge for high-quality perovskite NCs. Herein, fluoride ions are introduced into CsPbBr3 perovskite NCs at room temperature through the chelation of ligands. Experimental results demonstrate that these fluoride ions from inorganic salts can improve the average lifetime and crystallinity of CsPbBr3 NCs. Meanwhile, the resulting photoluminescence quantum yield is optimized up to 99.02%, and it has high stability to water, heat, and ultraviolet light. Density functional theory calculations show that fluoride ions have a higher binding energy compared to other ligands, which not only removes the electron trapping center but also increases the halogen ion migration energy. By mixing green-emission CsPbBr3 NCs and red-emission K2SiF6:Mn4+ phosphors on a blue chip, the fabricated white light emitting diode shows a high luminous efficiency of 147.8 lm/W, a wide color gamut (129% for NTSC), and CIE coordinates of (0.3160, 0.3051). Furthermore, the photoluminescence intensity decreased by only 2.9% after 48 h of continuous operation.

Understanding the Structural Dynamics of 2D/3D Perovskite Interfaces

The use of 2D perovskite capping layers to passivate the surface defects of 3D perovskite active layers has become ubiquitous in high performance lead halide perovskite solar cells. However, these 2D/3D interfaces can be highly dynamic, with the structure evolving to form various mixed dimensional phases when exposed to thermal stress or illumination. Changes in the photoluminescence spectrum of formamidinium lead iodide (FAPbI3) films capped with alkylammonium-based 2D perovskites as they age at 100 °C or under simulated 1 sun illumination indicate that the 2D perovskite transforms to progressively larger inorganic layer thicknesses (denoted by layer number n), eventually approaching a steady-state condition where only the 3D perovskite (n = ∞) is detectable. We find that this transformation slows by a factor of ∼2 when the length of the alkyl chain in the organic monoammonium ligand is increased from butylammonium to dodecylammonium. Furthermore, replacing dodecylammonium with its diammonium ligand counterpart, 1,12-dodecanediammonium, slows the structural transformation by 10-fold. These results point to the use of diammonium ligands as a possible pathway to form stable 2D/3D interfaces.

Activated Corrosion and Recovery in Lead Mixed-Halide Perovskites Revealed by Dynamic Near-Ambient Pressure X-ray Photoelectron Spectroscopy

Herein, we quantify rates of O2-photoactivated corrosion and recovery processes within triple cation CsFAMAPb(IBr)3 perovskite active layers using dynamic near-ambient pressure X-ray photoemission spectroscopy (NAP-XPS). Activated corrosion is described as iodide oxidation and lead reduction, which occurs only in the presence of both O2 and light through photoinduced electron transfer. We observe electron density reorganization from the Pb-I bonds consistent with ligand exchange, evident from the nonstoichiometric redox change (i.e., <1 e-). Approximately half of the Pb centers are reduced to weakly coordinated Pb-higher oxidation number than metallic Pb-with a rate coefficient of ∼3 (±0.3) × 10-4 atomic percent/s. Hole capture by I- yields I3- and is accompanied by increased concentrations of near-surface bromides, hypothesized to be due to anion vacancies and/or oxidation of mobile iodide resulting from ion demixing. Activated corrosion is found to be quasi-reversible; initial perovskite stoichiometry slowly recovers when the O2/light catalyst is removed, postulated to be due to mobile halide species present within the film below XPS sampling depth. Small deviations in near-surface composition (<2%) of the perovskite are used to connect reaction rates to quantified, near-band edge donor and acceptor defect concentrations, demonstrating two energetically distinct sites are responsible for the redox process. Collectively, environmental flux and rate quantification are deemed critical for the future elucidation of chemical degradation processes in perovskites, where rate-dependent reaction pathways are expected to be very system dependent (environment and material).

Conformationally Stable and Sterically Hindered Bicyclo[1.1.1]pentane-1,3-diammonium Modification of FAPbI3 Enhances the Performance of Perovskite Solar Cells

Solution-processed α-FAPbI3 perovskite films frequently exhibit structural defects and impurities that impede the durable operation of solar cells. In this study, we introduced a conformationally stable, sterically bulky molecular passivator, bicyclo[1.1.1]pentane-1,3-diammonium iodide (BCPDAI), by spin-coating from an isopropanol solution onto the perovskite film surface, followed by thermal annealing. This treatment effectively converted PbI2 and δ-FAPbI3 into a two-dimensional perovskite structure and significantly enhanced the crystal quality of α-FAPbI3. The BCPDAI-treated perovskite films exhibited smoother surface morphology and reduced trap densities for charge carriers, leading to improved power conversion efficiency in the solar cells. Notably, the BCPDAI-modified perovskite films provided the solar cells with enhanced operational stability. Theoretical calculations demonstrated that the high positive charge density of BCPDA2+ confers greater binding energy at the perovskite surface and elevates the diffusion activation energy of the iodide anion.

Low-Dimensional Hetero-Interlayer Enabling Sub-Bandgap Photovoltaic Conversion for Perovskite Solar Cells

Actualizing sub-band gap photovoltaic conversion is effective in remitting energy loss and pushing theoretical efficiency limits for perovskite solar cells (PSCs). Herein, a zero-dimensional organic metal halide based on hydroxyquinoline (HQ) is developed to sensitize PSCs for near-infrared region gain to implement sub-band gap photovoltaic conversion for enhancing power-conversion-efficiency (PCE) of PSCs. [ZnI4]2- skeletons containing heavy atoms intensify the direct singlet-to-triplet state transition of organic chromophores HQ. Meanwhile, the triplet energy of HQ is close to resonance with perovskite band gap, favoring the energy transfer to perovskite and exciting the additional electron-hole pairs, which was observed by transient absorption spectroscopy, confirming the sensitization of perovskite to increase sub-band gap photocurrent. HQ2ZnI4 modifies electronic and crystal structure, optimizes energy-level arrangement, and acts as a protective layer, realizing considerable PCEs in small (6.25 mm2)-/larger-area (1 cm2) devices and excellent operational stability. This low-cost strategy brings vitality to the light management of PSCs and expands low-dimensional materials.

In situ Polymerization Induced Seed-Root Anchoring Structure for Enhancing Stability and Efficiency in Perovskite Solar Modules

The escape of organic cations over time from defective perovskite interface leads to non-stoichiometric terminals, significantly affecting the stability of perovskite solar cells (PSCs). How to stabilize the interface composition under environmental stress remains a grand challenge. To address this issue, we utilize thiol-functionalized particles as a "seed" and conduct in situ polymerization of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA) as a "root" at the bottom of the perovskite layer. In this process, the thiol group acts as the initiation site for the polymerization of HFMA, while the fluorine groups in HFMA firmly anchor the organic cations of the perovskite through multiple hydrogen bonds. This strategy resembles how seeds take root in soil to prevent soil erosion. This bionic seed-rooting structure effectively stabilizes the stoichiometry of the perovskite, thus suppressing the escape of organic cations. As a result, the perovskite films with seed-rooting structures exhibit enhanced stability under harsh vacuum thermal conditions (150 °C, <10 Pa). The resulting PCS achieves an efficiency of 25.64 % and a 22.4 cm2 module efficiency of 22.61 %. After 1300 hours of 1-sun illumination at 85 % relative humidity and 65 °C (ISOS-L-3 protocol), the perovskite solar module maintains 90 % of its initial efficiency.

Dual-Passivation Strategy of Bulk and Surface Enables Highly Efficient and Stable Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) have captured significant interest due to their outstanding stability, cost-effective fabrication process, and good compatibility with flexible and tandem devices. The presence of bulk and surface defects is key factor in PSCs that cause non-radiative recombination and degradation. To improve the efficiency and stability of inverted PSCs, a bulk-to-surface dual-passivation strategy is employed by utilizing Oleylamine Iodide (OAmI) as additives and 4-Fluorobenzylamine Hydroiodide (4-F-PMAI) as surface passivating agents. Utilizing OAmI as bulk passivation can enhance the crystallinity of perovskite films and reduce lattice defects. Meanwhile, 4-F-PMAI further suppresses non-radiative recombination and reduces open-circuit voltage (VOC) loss through bidentate anchoring. Consequently, the dual-passivation strategy significantly enhances device performance, boosting the power conversion efficiency (PCE) of PSCs to 24.26%, with a VOC of 1.15V. Moreover, the unencapsulated PSCs show excellent long-term stability maintaining over 85% and 90% of the initial efficiency under 85 °C thermal annealing in N2 for 1000 hours and after storage in ambient conditions (RH: 30 ± 5%) for 1000 hours.

Highly Oriented Large-Grain 2D Cs3Bi2X9 Polycrystalline Films by an Isogenous-Lattice Homoepitaxy Strategy for Photodetection

Outstanding optoelectronic performances, including high carrier mobility and long carrier diffusion length, have only been observed in single-crystalline Cs3Bi2X9, which requires a lengthy fabrication process but not in the easily formed polycrystalline solids. This discrepancy arises from the disordered crystallization and the resultant unsatisfactory film quality. Herein, we propose an isogenous-lattice homoepitaxy strategy to induce the crystallization of highly oriented, large-grain two-dimensional (2D) Cs3Bi2X9 films via the in situ precrystallized, lattice-matched isogenous three-dimensional (3D) Cs2AgBiBr6 intermediate. The introduced 3D Cs2AgBiBr6 intermediate serves as a primer to initiate and direct the oriented epitaxy of 2D Cs3Bi2X9 while significantly retarding the crystallization process through an additional halogen exchange process, leading to films with grains over 1 μm in size and a highly consistent crystallization orientation. Consequently, the target films exhibit photophysical properties comparable to those of single crystals and superior photodetection performance.

Dipolar Carbazole Ammonium for Broadened Electric Field Distribution in High-Performance Perovskite Solar Cells

Perovskite solar cells (PSCs) with ammonium passivation exhibit superior device performance and stability. Beyond typical chemical passivation, ammonium salts control the electronic structure of perovskite surfaces, yet the molecular structure-property relationship requires further understanding, especially the dipole effect. Here, we employed carbazole and its halogenated counterpart as the functional group of ammonium salts. 2-Chloro-carbazol-9-ethylammonium iodide (CzCl-EAI) with a rigid, conjugated molecular structure further provides chemical passivation and enhances the ambient stability of perovskites. In addition, we found that halogenation enhances the intramolecular charge transfer for a larger molecular dipole moment, leading to the depletion region of perovskite films threefold wider than that of the PDAI2 condition. The power conversion efficiency (PCE) of inverted PSCs based on mixed passivation reached 25.16% and certified 24.35% under the quasi-steady-state (QSS) measurement. Unencapsulated devices retained over 91% of initial PCE under ISOS-D-2 conditions over 1100 h and maintained 80% of their initial performance after 500 h of continuous light illumination in ambient air with a 50-60% relative humidity (RH).

Controllable Heavy n-type Behaviours in Inverted Perovskite Solar Cells with Non-Conjugated Passivants

Interfacial issues between the perovskite film and electron transport layer greatly limit the efficiency and stability of inverted (p-i-n) perovskite solar cells (PSCs). Despite organic ammonium passivants have been widely established as interfacial layers, they failed to improve electron extraction. Here, we reported that the heavy n-type characteristics in a low band gap perovskite film could be modulated by incorporating non-conjugated ammonium passivants with strong electron-withdrawing abilities. This resulted in a significant enhancement of electron extraction in the heavily n-type doped perovskite. The passivant-treated PSCs exhibited a power conversion efficiency of 25.74 % with an excellent fill factor of 85.4 % and a high open-circuit voltage of 1.166 V, which are significantly higher than that of the control device. The unencapsulated devices maintained 88 % of their initial PCEs after 1,200 hours at 85 °C.

Formation Dynamics of Thermally Stable 1D/3D Perovskite Interfaces for High-Performance Photovoltaics

Direct understanding of the formation and crystallization of low-dimensional (LD) perovskites with varying dimensionalities employing the same bulky cations can offer insights into LD perovskites and their heterostructures with 3D perovskites. In this study, the secondary amine cation of N-methyl-1-(naphthalen-1-yl)methylammonium (M-NMA+) and the formation dynamics of its corresponding LD perovskite are investigated. The intermolecular π-π stacking of M-NMA+ and their connection with inorganic PbI6 octahedrons within the product structures control the formation of LD perovskite. In an N,N-dimethylformamide (DMF) precursor solution, both 1D and 2D products can be obtained. Interestingly, due to the strong interaction between M-NMA+ and the DMF solvent, compared to the 1D phase, the formation of 2D perovskites is uniquely dependent on heterogeneous nucleation. Nevertheless, post-treatment of 3D perovskite films with an isopropanol solution of M-NMAI leads to the exclusive formation of thermally stable 1D phases on the surface. The resulting 1D/3D heterostructure facilitates perovskite solar cells (PSCs) to not only achieve a record efficiency of 25.51% through 1D perovskite passivation but also significantly enhance the thermal stability of unencapsulated devices at 85 °C. This study deepens the understanding of the formation dynamics of LD perovskites and offers an efficient strategy for fabricating stable and high-performance PSCs.

First-Principles Study of Anionic Diffusion in Two-Dimensional Lead Halide Perovskite Lateral Heterostructures

Perovskite heterostructures have attracted wide interest for their photovoltaic and optoelectronic applications. The interdiffusion of halide anions leads to the poor stability and shorter lifetime of the halide perovskite heterostructures. Covering organic cations on the surface of perovskite heterostructures, the diffusion of ions can effectively be suppressed. However, the migration mechanism on two-dimensional lead halide perovskite lateral heterostructures under different organic cations remains inadequately explored. In this work, we performed first-principles calculations on the ion migration in two-dimensional (2D) lead halide perovskite lateral heterostructures with different interface defects and different cations. We found that the migration of iodine atoms across the interface in the heterostructures is more preferable than that of bromine atoms, regardless of the cations. Meanwhile, the migration of iodine atoms from the in-plane to the out-plane direction has the lowest energy barrier compared to other directions. Our calculations also reveal that both the type of cation and the migration path selected affect the energy barrier for anion migration, exhibiting either inhibitory or promoting effects. Specifically, the organic cation 345FAn, an ammonium ligand, showed an excellent promoting effect on the anion migration, while the BA cation exhibited an inhibiting effect. The calculated interdiffusion rate includes the interfacial single bromine vacancy, which is consistent with previous experimental observations. However, the heterostructures with interfacial single iodine defects exhibit a higher interdiffusion rate. Our findings on the ion migration mechanism in lead halide perovskite lateral heterostructures contribute to both experimental discussions and theoretical insights.

Band Gap Narrowing in Lead-Halide Perovskites by Dynamic Defect Self-Doping for Enhanced Light Absorption and Energy Upconversion

Metal halide perovskites (MHP) have attracted great attention in the photovoltaic industry due to their high and rapidly rising power conversion efficiencies, currently over 25%. However, hybrid organic-inorganic MHPs are inherently chemically unstable, limiting their application. All-inorganic MHPs perovskites, such as CsPbI3, have many merits, but their stable conversion efficiency is lower, around 18%, due to a larger band gap causing a mismatch with the solar spectrum. Choosing α-CsPbI3 as a prototypical system, we demonstrate a new general concept of dynamic defects that fluctuate between deep and shallow states, and increase the range of absorbed solar photons, without accelerating the nonradiative electron-hole recombination. In their deeper energy state, the defects narrow the band gap and allow the harvesting of light with longer wavelengths. Fluctuating to shallower energies, the defects allow the escape of photogenerated charges into bands, enabling charge transport and resulting in the defect-mediated upconversion of thermal energy into electricity. Defect covalency and participation of low-frequency anharmonic vibrations decouple trapped charges from free charge carriers, minimizing nonradiative charge carrier losses. Our findings demonstrate that defect covalency and defect dynamics are unique and important properties of MHPs, and can be used to optimize MHPs for efficient solar energy harvesting and optoelectronic applications.

Solvent-dripping modulated 3D/2D heterostructures for high-performance perovskite solar cells

The controlled growth of two-dimensional (2D) perovskite atop three-dimensional (3D) perovskite films reduces interfacial recombination and impedes ion migration, thus improving the performance and stability of perovskite solar cells (PSCs). Unfortunately, the random orientation of the spontaneously formed 2D phase atop the pre-deposited 3D perovskite film can deteriorate charge extraction owing to energetic disorder, limiting the maximum attainable efficiency and long-term stability of the PSCs. Here, we introduce a meta-amidinopyridine ligand and the solvent post-dripping step to generate a highly ordered 2D perovskite phase on the surface of a 3D perovskite film. The reconstructed 2D/3D perovskite interface exhibits reduced energetic disorder and yields cells with improved performance compared with control 2D/3D samples. PSCs fabricated with the meta-amidinopyridine-induced phase-pure 2D perovskite passivation show a maximum power conversion efficiency of 26.05% (a certified value of 25.44%). Under damp heat and outdoor tests, the encapsulated PSCs maintain 82% and 75% of their initial PCE after 1000 h and 840 h, respectively, demonstrating improved practical durability.

Simultaneous Suppression of Multilayer Ion Migration via Molecular Complexation Strategy toward High-Performance Regular Perovskite Solar Cells

The migration and diffusion of Li+, I- and Ag impedes the realization of long-term operationally stable perovskite solar cells (PSCs). Herein, we report a multifunctional and universal molecular complexation strategy to simultaneously stabilize hole transport layer (HTL), perovskite layer and Ag electrode by the suppression of Li+, I- and Ag migration via directly incorporating bis(2,4,6-trichlorophenyl) oxalate (TCPO) into HTL. Meanwhile, TCPO co-doping results in enhanced hole mobility of HTL, advantageous energy band alignment and mitigated interfacial defects, thereby leading to facilitated hole extraction and minimized nonradiative recombination losses. TCPO-doped regular device achieves a peak power conversion efficiency (PCE) of 25.68 % (certified 25.59 %). The unencapsulated TCPO doped devices maintain over 90 % of their initial efficiencies after 730 h of continuous operation under one sun illumination, 2800 h of storage at 30 % relative humidity, and 1200 h of exposure to 65 °C, which represents one of the best stabilities reported for regular PSCs. This work provides a new approach to enhance the PCE and long-term stability of PSCs by host-guest complexation strategy via rational design of multifunctional ligand molecules.

Dimensional engineering of interlayer for efficient large-area perovskite solar cells with high stability under ISOS-L-3 aging test

The utilization of low-dimensional perovskites (LDPs) as interlayers on three-dimensional (3D) perovskites has been regarded as an efficient strategy to enhance the performance of perovskite solar cells. Yet, the formation mechanism of LDPs and their impacts on the device performance remain elusive. Herein, we use dimensional engineering to facilitate the controllable growth of 1D and 2D structures on 3D perovskites. The differences of isomeric ligands in electrostatic potential distribution and steric effects for intermolecular forces contribute to different LDPs. The 1D structure facilitates charge transfer with favored channel orientation and energy level alignment. This approach enables perovskite solar modules (PSMs) using 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene to achieve an efficiency of 20.20% over 10 by 10 square centimeters (cm2) and 22.05% over 6 by 6 cm2. In particular, a PSM (6 by 6 cm2) using poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] maintains an initial efficiency of ~95% after 1000 hours under the rigorous ISOS-L-3 accelerated aging tests, marking a record for the highest stability of n-i-p structure modules.

Thermally Stable Anthracene-Based 2D/3D Heterostructures for Perovskite Solar Cells

Bulky organic cations are used in perovskite solar cells as a protective barrier against moisture, oxygen, and ion diffusion. However, bulky cations can introduce thermal instabilities by reacting with the near-surface of the 3D perovskite forming low-dimensional phases, including 2D perovskites, and by diffusing away from the surface into the film. This study explores the thermal stability of Cs0.09FA0.91PbI3 3D perovskite surfaces treated with two anthracene salts─anthracen-1-ylmethylammonium iodide (AMAI) and 2-(anthracen-1-yl)ethylammonium iodide (AEAI)─and compares them with the widely used phenethylammonium iodide (PEAI). The steric hindrance of AMAI limits the interaction of its NH3+ head with the perovskite lattice, relative to what is seen with AEAI and PEAI. As a result, AMAI requires more thermal energy to convert the 3D perovskite surface to a 2D perovskite. Annealing of perovskite surfaces treated with the iodide salts results in decreased power conversion efficiencies (PCEs) for PEAI and AEAI, while a PCE enhancement is observed for AMAI. Importantly, AMAI-treated devices show enhanced stability upon annealing of the film and a 100% yield of working pixels after a high-temperature stability test at 85 °C, representing the most reliable device configuration among all those studied in this work. These results reveal the potential of AMAI as a scalable surface treatment.

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect

Additive engineering plays a pivotal role in achieving high-quality light-absorbing layers for high-performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom-synthesized 2-ureido-4-pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the -OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead-iodide antisite defects, alleviating hysteresis, and reducing non-radiative recombination. Furthermore, the enhanced C=O and -NH2 motifs interact with the A-site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open-circuit voltage of the UPy-based p-i-n PSCs reaches 1.20 V, and the fill factor surpasses 84 %. The champion device delivers a power conversion efficiency of 25.75 %. Remarkably, the unencapsulated device maintained 96.9 % and 94.5 % of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1-sun illumination, respectively.

Air-Processed Efficient Perovskite Solar Cells With Full Lifecycle Management

Despite the outstanding power conversion efficiency of perovskite solar cells (PSCs) realized over the years, the entire lifecycle from preparation and operation to discarding of PSCs still needs to be carefully considered when it faces the upcoming large-scale production and deployment. In this study, bio-derived chitin-based polymers are employed to realize the full lifecycle regulation of air-processed PSCs by forming multiple coordinated and hydrogen bonds to stabilize the lead iodide and organic salt precursor inks, accelerating the solid-liquid reaction and crystallization of two-step deposition process, then achieving the high crystalline and oriented perovskites with less notorious charge defects in the open air. The air-prepared PSCs exhibit a decent efficiency of 25.18% with high preparation reproducibility and improved operational stability toward the harsh environment and mechanical stress stimuli. The modified PSCs display negligible fatigue behavior with keeping 92% of its initial efficiency after operating for 32 diurnal cycles (ISOS-LC-1 protocol). Meanwhile, closed-loop lead management of end-of-life PSCs including suppression of lead leakage, toxicity evaluation of broken devices, and recycling of lead iodide components are comprehensively investigated. This work sheds light on a promising avenue to realize the entire lifecycle regulation of air-processed efficient and stable PSCs.

Synergistic Modulation of Orientation and Steric Hindrance Induced by Alkyl Chain Length in Ammonium Salt Passivator Toward High-performance Inverted Perovskite Solar Cells and Modules

Organic ammonium salts are extensively utilized for passivating surface defects in perovskite films to mitigate trap-assisted nonradiative recombination. However, the influence of alkyl chain length on the molecular orientation and spatial steric hindrance of ammonium salt remains underexplored, hindering advancements in more effective passivators. Here, a series of organic ammonium salts is reported with varying alkyl chain lengths to passivate surface defects and optimize band alignment. It is revealed that long alkyl chains promote parallel molecular orientation on the perovskite surface, thereby reinforcing interaction with surface defects, whereas excessive chain length introduces steric hindrance, weakening anion-perovskite interactions. Nonylammonium acetate (NAAc) with optimal chain length achieves the ideal balance between chemical interactions, resulting in superior passivation. Through NAAc passivation, high-performance inverted perovskite solar cells (PSCs) and modules are achieved, with power conversion efficiencies (PCE) of 25.79% (certified 25.12%) and 19.62%, respectively. This marks a record PCE for inverted PSCs utilizing vacuum flash technology in ambient conditions. Additionally, the NAAc-passivated devices retain 91% of their initial PCE after 1200 h of continuous maximum power point operation. This work offers new insights into the interplay between molecular orientation and steric hindrance, advancing the design of high-performance PSCs.

Synergistic Doping Strategy with Novel Multi-Carbonyl Conductive Polymer Enables Stable Self-Powered Perovskite Photodetectors

Lead halide perovskites hold immense promise for optoelectronic applications but still suffer from instability caused by defects. The defects are mainly generated from the film fabrication processes and halide ion migration during long-term storage. Here, a synergistic doping strategy is proposed to enhance the stability of perovskites. A novel multi-carbonyl conductive polymer, poly(benzodifurandione) (PBFDO), is incorporated into the precursor solution to effectively passivate the unoccupied Pb2+ defects in perovskite films and promote the continuous growth of perovskites. An organic iodide, thiophene-2-ethylammonium iodide (TEAI), is doped in the transport layer to inhibit the halide ion migration and enhance the stability of perovskites synergistically. Self-powered photodetectors are constructed with improved stability, maintaining ≈90% of their initial photocurrents after being stored for ≈87 days in a humid atmosphere with 60% relative humidity. The optimized photodetectors show a high detectivity of 8.1 × 1012 Jones at 680 nm wavelength, wide linear dynamic range of 121.9 dB, and fast response with a rise/fall time of 1.92/1.17 µs. A reflection-mode perovskite photoplethysmography testing system is developed, achieving high heart rate testing capabilities. This work suggests the great potential of perovskite photodetectors for noninvasive medical monitoring applications.

Stable Surface Contact with Tailored Alkylamine Pyridine Derivatives for High-Performance Inverted Perovskite Solar Cells

Formamidinium-cesium lead triiodide (FA1-xCsxPbI3) perovskite holds great promise for perovskite solar cells (PSCs) with both high efficiency and stability. However, the defective perovskite surfaces induced by defects and residual tensile strain largely limit the photovoltaic performance of the corresponding devices. Here, the passivation capability of alkylamine-modified pyridine derivatives for the surface defects of FA1-xCsxPbI3 perovskite is systematically studied. Among the studied surface passivators, 3-(2-aminoethyl)pyridine (3-PyEA) with the suitable size is demonstrated to be the most effective in reducing surface iodine impurities and defects (VI and I2) through its strong coordination with Npyridine. Additionally, the tail amino group (─NH2) from 3-PyEA can react with FA+ cations to reduce the surface roughness of perovskite films, and the reaction products can also passivate FA vacancies (VFA), and further strengthen their binding interaction to perovskite surfaces. These merits lead to suppressed nonradiative recombination loss, the release of residual tensile stress for the perovskite films, and a favorable energy-level alignment at the perovskite/[6,6]-phenyl-C61-butyric acid methyl ester interface. Consequently, the resulting inverted FA1-xCsxPbI3 PSCs obtain an impressive power conversion efficiency (PCE) of 25.65% (certified 25.45%, certified steady-state efficiency 25.06%), along with retaining 96.5% of the initial PCE after 1800 h of 1-sun operation at 55 °C in air.

Charge Transfer and Retention in 2D Passivated Perovskite-C60 Systems

2D perovskites and organic ligands are often implemented as passivating interlayers in perovskite solar cells. Herein, five such passivates are evaluated by using time-resolved spectroscopy to study the carrier dynamics at the perovskite-C60 interface. The impact of passivation on factors such as charge transfer rate, charge retention in the acceptor layers, surface recombination, and uniformity are mapped onto the solar cell performance. The charge transfer was found to take place in tens of nanoseconds, and the charge retention without any passivate lasted a few hundred nanoseconds. The passivate that produced the best solar cells, ethylenediammonium iodide, extended the charge retention time up to one microsecond, which significantly increased the open-circuit voltage. It also had the best uniformity and hence least variance in power conversion efficiency. Curiously, it did not merely adjust surface energy states to enhance charge transfer but also extracted charges by itself without the C60, resulting in higher short-circuit current.

Enhanced Efficiency and Stability of Triple-Cation Perovskite Solar Cells through Engineering of the Cell Interface with Phenylethylammonium Thiocyanate

It is reported that the tricationic mixed halide perovskite Csx(FAyMA1-y)1-xPb(IzBr1-z)3 (CsFAMA) possesses a stable crystal structure and outstanding bandgap tunability, rendering it one of the most competitive candidates for commercial perovskite solar cells (PSCs). Nevertheless, the numerous defects at the interface of the tricationic perovskite give rise to a significant constraint on the light capture performance of the device. Simultaneously, water molecules form intermediate compounds with the perovskite at the interface via hydrogen bonds, accelerating the degradation of the perovskite. This study reports the introduction of two-dimensional (2D) phenylethylthiocyanate (PEASCN) at the interface of three-dimensional (3D) perovskite. This approach significantly passivates the surface defects of the perovskite. Concurrently, due to the propensity of the organic ammonium cation PEA+ to interact with the FA+ base within the perovskite, SCN- is exposed outward to form a small-molecule hydrophobic layer. This method markedly reduces the loss of charge recombination and significantly enhances the device stability. The results indicate that the efficiency of the conventional device treated solely with PEASCN is as high as 23.94%. The unsealed device retains 85.12% of its initial efficiency after being placed in a conventional environment for 500 h. Furthermore, this surface passivation and hydrophobic strategy can be universally applicable to perovskite types with a high FA+ content.

Molecularly tailorable metal oxide clusters ensured robust interfacial connection in inverted perovskite solar cells

Interfacial recombination and ion migration between perovskite and electron-transporting materials have been the persisting challenges in further improving the efficiency and stability of perovskite solar cells (PVSCs). Here, we design a series of molecularly tailorable clusters as an interlayer that can simultaneously enhance the interaction with C60 and perovskite. These clusters have precisely controlled structures, decent charge carrier mobility, considerable solubility, suitable energy levels, and functional ligands, which can help passivate perovskite surface defects, form a uniform capping net to immobilize C60, and build a robust coupling between perovskite and C60. The target inverted PVSCs achieve an impressive power conversion efficiency (PCE) of 25.6% without the need for additional surface passivation. Crucially, the unencapsulated device displays excellent stability under light, heat, and bias, maintaining 98% of its initial PCE after 1500 hours of maximum power point tracking. These results show great promise in the development of advanced interfacial materials for highly efficient perovskite photovoltaics.

Surface reconstruction of wide-bandgap perovskites enables efficient perovskite/silicon tandem solar cells

Wide-bandgap perovskite solar cells (WBG-PSCs) are critical for developing perovskite/silicon tandem solar cells. The defect-rich surface of WBG-PSCs will lead to severe interfacial carrier loss and phase segregation, deteriorating the device's performance. Herein, we develop a surface reconstruction method by removing the defect-rich crystal surface by nano-polishing and then passivating the newly exposed high-crystallinity surface. This method can refresh the perovskite/electron-transporter interface and release the residual lattice strain, improving the charge collection and inhibiting the ion migration of WBG perovskites. As a result, we can achieve certified efficiencies of 23.67% and 21.70% for opaque and semi-transparent PSCs via a 1.67-eV perovskite absorber. Moreover, we achieve four-terminal perovskite/silicon tandem solar cells with a certified efficiency of 33.10% on an aperture area of one square centimeter.

Constructing Bionic Perovskite Smart Photovoltaic Windows with Switchable Colors and High Cycling Stability

Smart photovoltaic windows (SPWs) provide a high-efficiency and energy-saving strategy owing to the dual capabilities of electricity generation and sunlight modulation achieved by tunable colors and transmittances. Due to the deterioration of chromic process on photovoltaic layers, SPWs usually suffer from poor cycling stability. Moreover, thermochromic SPWs with a multilayer structure usually change transmittance without reversible color transitions. To address these issues, inspired by chameleon skin, bionic SPWs are designed and constructed by integrating hydrogel, CsPbBr3 semitransparent perovskite solar cells (ST-PSCs), and transparent polymer film. The SPWs realize reversible transitions between transparent green (25 °C) and opaque yellow (45 °C) states in a short duration (2 min) under natural conditions. By optimizing perovskite film and ultrathin-metal electrodes, CsPbBr3 ST-PSCs achieve a good trade-off between transmittance and efficiency, delivering the highest photovoltaic efficiency (8.35%) and a record light utilization efficiency (4.43). Ultimately, the multilayer SPWs maintain stable optical properties and more than 88% initial conversion efficiency after 100 transition cycles, presenting excellent cycling stability. This study proposes a novel approach and device structure for SPWs with high cycling stability, switchable colors, and switchable transmittances. It also paves the way for smart photovoltaic deployment in buildings and many other fields.

Exploring the Potential and Hurdles of Perovskite Solar Cells with p-i-n Structure

The p-i-n architecture within perovskite solar cells (PSCs) is swiftly transitioning from an alternative concept to the forefront of perovskite photovoltaic technology, driven by significant advancements in performance and suitability for tandem solar cell integration. The relentless pursuit to increase efficiencies and understand the factors contributing to instability has yielded notable strategies for enhancing p-i-n PSC performance. Chief among these is the advancement in passivation techniques, including the application of self-assembled monolayers (SAMs), which have proven central to mitigating interface-related inefficiencies. This Perspective delves into a curated selection of recent impactful studies on p-i-n PSCs, focusing on the latest material developments, device architecture refinements, and performance optimization tactics. We particularly emphasize the strides made in passivation and interfacial engineering. Furthermore, we explore the strides and potential of p-i-n structured perovskite tandem solar cells. The Perspective culminates in a discussion of the persistent challenges facing p-i-n PSCs, such as long-term stability, scalability, and the pursuit of environmentally benign solutions, setting the stage for future research directives.

Perovskite/silicon tandem solar cells with bilayer interface passivation

Two-terminal monolithic perovskite/silicon tandem solar cells demonstrate huge advantages in power conversion efficiency compared with their respective single-junction counterparts1,2. However, suppressing interfacial recombination at the wide-bandgap perovskite/electron transport layer interface, without compromising its superior charge transport performance, remains a substantial challenge for perovskite/silicon tandem cells3,4. By exploiting the nanoscale discretely distributed lithium fluoride ultrathin layer followed by an additional deposition of diammonium diiodide molecule, we have devised a bilayer-intertwined passivation strategy that combines efficient electron extraction with further suppression of non-radiative recombination. We constructed perovskite/silicon tandem devices on a double-textured Czochralski-based silicon heterojunction cell, which featured a mildly textured front surface and a heavily textured rear surface, leading to simultaneously enhanced photocurrent and uncompromised rear passivation. The resulting perovskite/silicon tandem achieved an independently certified stabilized power conversion efficiency of 33.89%, accompanied by an impressive fill factor of 83.0% and an open-circuit voltage of nearly 1.97 V. To the best of our knowledge, this represents the first reported certified efficiency of a two-junction tandem solar cell exceeding the single-junction Shockley-Queisser limit of 33.7%.

Cation reactivity inhibits perovskite degradation in efficient and stable solar modules

Perovskite solar modules (PSMs) show outstanding power conversion efficiencies (PCEs), but long-term operational stability remains problematic. We show that incorporating N,N-dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]+) cation effectively improved perovskite film. The in situ formation of [MTTZ]+ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. The optimized PSMs achieved a record (certified) PCE of 23.2% with an aperture area of 27.2 cm2, with a stabilized PCE of 23.0%. The encapsulated PSM retained 87.0% of its initial PCE after ~1900 hours of maximum power point tracking at 85°C and 85% relative humidity under 1.0-sun illumination.

Buried Interface Strategies with Covalent Organic Frameworks for High-Performance Inverted Perovskite Solar Cells

Simultaneously controlling defects and film morphology at the buried interface is a promising approach to improve the power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs). Here, two new donor‒acceptor type semiconductive covalent organic frameworks (COFs) are developed, COFTPA and COFICZ. The carefully designed COFs structure not only effectively regulates the morphology and defects of the buried interface film, but also realizes the alignment with the energy level of the perovskite film and enhances the extraction and transmission of the interface charge. Among them, COFICZ-treated inverted PSCs achieved a maxmum PCE of 25.68% (certified 25.14%), the inverted PCE reached a minimum PCE of 22.92% for 1 cm2 device. The efficiency of inverted PSCs with a 1.68 eV wide bandgap reached 22.92%, which is the highest datum of the reported 1.68 eV wide bandgap PSC. This lays the groundwork for the commercialization of perovskite/silicon tandem solar cells. Additionally, the unencapsulated devices demonstrated a high degree of stability during operational use and when subjected to conditions of high humidity and temperature.

Coherent growth of high-Miller-index facets enhances perovskite solar cells

Obtaining micron-thick perovskite films of high quality is key to realizing efficient and stable positive (p)-intrinsic (i)-negative (n) perovskite solar cells1,2, but it remains a challenge. Here we report an effective method for producing high-quality, micron-thick formamidinium-based perovskite films by forming coherent grain boundaries, in which high-Miller-index-oriented grains grow on the low-Miller-index-oriented grains in a stabilized atmosphere. The resulting micron-thick perovskite films, with enhanced grain boundaries and grains, showed stable material properties and outstanding optoelectronic performances. The small-area solar cells achieved efficiencies of 26.1%. The 1-cm2 devices and 5 cm × 5 cm mini-modules delivered efficiencies of 24.3% and 21.4%, respectively. The devices processed in a stabilized atmosphere presented a high reproducibility across all four seasons. The encapsulated devices exhibited superior long-term stability under both light and thermal stressors in ambient air.

Leveraging ordered voids in microporous perovskites for intercalation and post-synthetic modification

We report the use of porous organic layers in two-dimensional hybrid organic-inorganic perovskites (HOIPs) to facilitate permanent small molecule intercalation and new post-synthetic modifications. While HOIPs are well-studied for a variety of optoelectronic applications, the ability to manipulate their structure after synthesis is another handle for control of physical properties and could even enable use in future applications. If designed properly, a porous interlayer could facilitate these post-synthetic transformations. We show that for a series of copper-halide perovskites, a crystalline arrangement of designer ammonium groups allows for permanently porous interlayer space to be accessed at room temperature. Intercalation of the electroactive molecules ferrocene and tetracyanoethylene into this void space can be performed with tunable loadings, and these intercalated perovskites are stable for months. The porosity also enables reactivity at the copper-halide layer, allowing for facile halide replacement. Through this, we access previously unobserved reactivity with halogens to perform halide substitution, and even replace halides with pseudohalides. In the latter case, the porous structure allows for stabilization of new phases, specifically a novel copper-thiocyanate perovskite phase, only accessible through post-synthetic modification. We envision that this broad design strategy can be expanded to other industrially relevant HOIPs to create a new class of highly adjustable perovskites.

Customizing Aniline-Derived Molecular Structures to Attain beyond 22 % Efficient Inorganic Perovskite Solar Cells

The characteristics of the soft component and the ionic-electronic nature in all-inorganic CsPbI3-xBrx perovskite typically lead to a significant number of halide vacancy defects and ions migration, resulting in a reduction in both photovoltaic efficiency and stability. Herein, we present a tailored approach in which both anion-fixation and undercoordinated-Pb passivation are achieved in situ during crystallization by employing a molecule derived from aniline, specifically 2-methoxy-5-trifluoromethylaniline (MFA), to address the above challenges. The incorporation of MFA into the perovskite film results in a pronounced inhibition of ion migration, a significant reduction in trap density, an enhancement in grain size, an extension of charge carrier lifetime, and a more favorable alignment of energy levels. These advantageous characteristics contribute to achieving a champion power conversion efficiency (PCE) of 22.14 % for the MFA-based CsPbI3-xBrx perovskite solar cells (PSCs), representing the highest efficiency reported thus far for this type of inorganic metal halide perovskite solar cells, to the best of our knowledge. Moreover, the resultant PSCs exhibits higher environmental stability and photostability. This strategy is anticipated to offer significant advantages for large-area fabrication, particularly in terms of simplicity.

Long-term stability in perovskite solar cells through atomic layer deposition of tin oxide

Robust contact schemes that boost stability and simplify the production process are needed for perovskite solar cells (PSCs). We codeposited perovskite and hole-selective contact while protecting the perovskite to enable deposition of SnOx/Ag without the use of a fullerene. The SnOx, prepared through atomic layer deposition, serves as a durable inorganic electron transport layer. Tailoring the oxygen vacancy defects in the SnOx layer led to power conversion efficiencies (PCEs) of >25%. Our devices exhibit superior stability over conventional p-i-n PSCs, successfully meeting several benchmark stability tests. They retained >95% PCE after 2000 hours of continuous operation at their maximum power point under simulated AM1.5 illumination at 65°C. Additionally, they boast a certified T97 lifetime exceeding 1000 hours.

Effectiveness of 2-Terminal Perovskite/Perovskite/c-Si Triple-Junction Solar Cells: An Integrated Study with an Emphasis on Methylammonium Bismuth Iodide

The growing interest in high-efficiency solar energy technologies has driven research on multijunction solar cells to flourish over the last several years. This study sheds light on the optical, structural, and morphological aspects of the (CH3NH3)3Bi2I9 ((MA)3Bi2I9) film by fabricating and analyzing it experimentally. This thorough investigation lays the groundwork for more research into the film's possible uses in solar cell technology. We performed simulations to enhance the efficiency of two-terminal (2T) perovskite/perovskite double junction and perovskite/perovskite/c-Si triple-junction solar cells (TJSC) by using the MA3Bi2I9 material. The power conversion efficiency was greatly increased by using 2T triple-junction solar cells; the increase was around 116.59% from single junction (13.80-29.89%) and 31.91% from double junction (22.66-29.89%). As far as we know, this is the first investigation of the efficacy of MA3Bi2I9 as a top layer in multijunction tandem configurations. This revolutionary approach allows both academics and industry experts to produce cost-effective and efficient tandem solar cells, thereby enhancing earth-based solar energy development.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.