A crystal capping layer for formation of black-phase FAPbI3 perovskite in humid air

Fluid Chemistry of Metal Halide Perovskites

Solution-processed metal halide perovskites (MHPs) have been rapidly developed worldwide, with much attention to fluid dynamic, fluid crystallization, and fluid interfaces, all falling within the realm of fluid chemistry. It is widely recognized that the theory of fluid chemistry has been proven to provide an effective means for the improvement of perovskite crystallization and the enhancement of perovskite solar cells (PSCs) performance. In this review, the fluid behavior, microfluidic synthesis, and aging process of perovskite materials are first investigated, with emphasis on the related improvement methods and chemical mechanisms. Second, the internal crystallization chemistry, external interface chemistry, and the large-area PSCs based on the fluid chemistry are discussed. Finally, four specific directions for future studies of fluid chemistry of MHPs are proposed, aiming to harness the theoretical advantages of fluid chemistry and contribute to the industrialization of PSCs.

Interface Field-Effect Passivation Enabled by Selectively Extruded Cations for Printable Mesoscopic Perovskite Solar Cells with Improved Performance

Mesoporous electron transport layer (ETL) in printable mesoscopic perovskite solar cells (p-MPSCs) enables rapid and selective extraction of photogenerated electrons and facilitates device fabrication without a hole transport layer (HTL). However, the inherent mesoporous architecture introduces abundant interfacial defects that promote undesired non-radiative recombination, limiting the power conversion efficiency (PCE). To address this challenge, an interface field-effect passivation strategy is implemented, leveraging spatially selective cation extrusion. By incorporating tetraphenylphosphonium cations, sterically bulky organic ions that migrate to the perovskite/ETL interface during crystallization, a robust interfacial electrostatic field is introduced. This field simultaneously suppresses the non-radiative recombination by inducing field-effect passivation and enhances the charge extraction through optimizing energy alignment. The synergistic effects yield a PCE enhancement from 19.4% to 21.0%. This work underscores the potential of cation-engineered interfacial fields to improve the performance of HTL-free carbon-electrode perovskite photovoltaics.

Employment of l-Citrulline as an Effective Molecular Bridge for Regulating the Buried Interface of Perovskite Solar Cells to Achieve High Efficiency and Good Stability

Suppressing the defects from SnO2 and perovskite interface is essential for the fabrication of large-area n-i-p perovskite solar cells (PSCs) with the needed lifetime and efficiency for commercialization. Here, we report the employment of l-citrulline (CIT), which has amino acid (─COOH, ─NH2) and urea (─NH─CO─NH2) groups, during SnO2 colloidal dispersion to function as a molecular bridge to modulate the SnO2/perovskite buried interface. The amino acid group can effectively coordinate with Sn4+ to passivate the oxygen vacancy defects of SnO2, and the urea group can interact with uncoordinated Pb2+ and I-. These interactions not only improve the electron mobility of SnO2 but also facilitate the formation of larger grain-size perovskite film. In addition, they can also inhibit the generation of excess PbI2 and the nonphotoactive δ phase to result in suppressed trap-assisted nonradiative recombination. Consequently, the incorporation of CIT helps achieve a champion power conversion efficiency (PCE) of 25.95% (0.07065 cm2) in PSC with improved shelf life/light soaking stability. When combined with an antisolvent-free slot-die coating technique in air, the solar modules (23.26 cm2) could achieve a PCE of 22.70%, which is among the highest PCE reported so far.

Optimizing the Distribution of Additive to Refine the Micro-Nanostructure of Perovskite Films via Pulsed Laser Processing

Additives have found widespread application in perovskite optoelectronic devices, playing a crucial role in enhancing the performance and stability of these devices by optimizing the crystallization kinetics of the perovskite. However, the nonuniform distribution of additives in perovskite films caused by the bottom-up volatilization of low-boiling-point additives during traditional thermal annealing is a challenging issue that needs to be solved. In this work, we propose a strategy that integrates laser processing technology with the dithieno[3,2-b:2',3'-d]thiophene (DTT) additive process, which enables it to reduce defects by interacting with the octahedral inorganic framework of perovskite. Initially, the micro-nanostructure of the perovskite film is enhanced by the fast crystallization induced by high-energy pulsed laser irradiation, which in turn modulates the evaporation of the solution to regulate the distribution of DTT. Concurrently, the shock pressure generated by the pulsed laser further restricts the accumulation of DTT and promotes its uniform distribution within the perovskite film. As a result, by optimizing the crystallization kinetics of perovskite through pulsed laser and DTT, the crystal structure and electronic structure optimization of perovskite film lead to a reduction in defect density. The optimization of carrier dynamics further enhances the performance of the device with an excellent T80 stability of about 2400 h. This approach will provide a technical framework and theoretical basis for controlling the perovskite crystal growth and defect passivation to achieve large-scale commercial applications.

Surface Passivation and Energy Alignment Modulation of n-i-p Perovskite Solar Cells with Self-Assembled Molecule

Perovskite's surface defects trigger deep level traps and energy misalignment, resulting in substantial interface recombination and energy loss in perovskite solar cells (PSCs). Herein, 9-fluoreneacetic acid (FAA), a self-assembled molecule (SAM), is employed to passivate the interface defects and modulate energy alignment. SAM modification reduces the defect density from 6.37  ×  1015 to 3.11  ×  1015 cm-3 and produces a p-type surface with an upward band bending, thus constructing a well-defined n-i-p heterojunction for efficient charge separation. Accordingly, the target PSC realizes 24.75% power conversion efficiency (PCE) and retains 92% for 1100 h during maximum power point tracking (MPPT) at room temperature. Furthermore, over 80% of initial PCE has been reserved after 2500 h aging in 25-30% relative humidity (RH). This SAM strategy is expected to enhance the efficiency and stability for n-i-p PSCs.

Gas sensing by long-wavelength and long-afterglow pectin/melamine-formaldehyde aerogel via resonance energy transfer

The exploration of pure organic ultra-long room temperature phosphorescence (RTP) materials has emerged as a research hotspot in recent years. Herein, a simple strategy for fabricating long-afterglow polymer aerogels with three-dimensional ordered structures and environmental monitoring capabilities is proposed. Based on the non-covalent interactions between pectin (PC) and melamine formaldehyde (MF), a composite aerogel (PCMF@phenanthrene) (PCMF@PA) doped with phosphorescent organic small molecules was constructed. It exhibits a stable and persistent afterglow, with a phosphorescence lifetime reaching up to 1.99 s. Simultaneously, this aerogel possesses excellent mechanical properties, having a compressive modulus of 4.14 MPa, which is 490.8 times that of the PC aerogel. Its friction coefficient is also much lower than that of the single MF aerogel, enabling the material to achieve a better balance between rigidity and service life in practical applications. Moreover, through resonance energy transfer, the afterglow wavelength was redshifted from 504 nm to 576 nm and 620 nm, and aerogels with ultra-long yellow and red afterglows were successfully obtained. PCMF@PA aerogels display specific chemical stability in different organic solvents. Notably, PCMF@PA has a characteristic recognition for formic acid gas. The change in the luminous intensity and lifetime of the aerogel after gas absorption distinguishes it from gases such as ammonia and acetic acid. These phosphorescent polymer aerogels with self-monitoring and tracing capabilities not only foster the advancement of ordered phosphorescent materials but also broaden the application scope of RTP materials in environmental monitoring.

High-Oriented SnO2 Nanocrystals for Air-Processed Flexible Perovskite Solar Cells with an Efficiency of 23.87

Tin (IV) oxide (SnO2) electron transport layer (ETL) emerges as the most promising n-type semiconductor material for flexible perovskite solar cells (f-PSCs). The (110) facet-dominated SnO2 colloids are readily created, whereas other best-performing (101) and (200) facets-dominated ones with superior potential in interface modulation and lattice matching remain insufficiently explored. Here water-soluble acryloyloxyethyltrimethyl ammonium chloride-acrylamine (DAC-AA) doping into SnO2 colloids produces more (101)- and (200)-oriented crystal domains through lowering surface absorption energy and offering additional thermodynamic driving force. Theoretical and experimental analyses corroborate that the grain preference orientation induced by DAC-AA modification strengthens heating transfer rate on the flexible substrate and favors lattice matching of perovskite (100) plane on SnO2 (101) and (200) facets. Accordingly, the champion f-PSCs on high-oriented SnO2-DAC-AA ETLs fabricated fully in ambient air conditions achieve the efficiencies of 23.87% and 22.41% with aperture areas of 0.092 and 1 cm2. In parallel, the propitious interfacial lattice arrangement attenuates the formation of micro-strain inside perovskite films, maintaining 92.5% of their initial performance after 10 000 bending cycles with a curvature radius of 6 mm.

Robust Fully Screen-Printed Perovskite Solar Cells Based on Synergistic Ostwald Ripening

Fully screen-printed process for low-cost manufacturing significantly enhances the commercial competitiveness of perovskite solar cells (PSCs). However, the controllable crystallization in screen-printed perovskite thin films using high-viscosity ionic liquids has been suggested to be difficult, which hampers further development of fully screen-printed perovskite devices in terms of application expansion and performance improvement. Here, we report a synergistic ripening strategy to fully control crystallization by employing methylamine propionate (MAPa) ionic liquid and water (H2O, moisture in the air). We found that a reversible and sustainable ripening process was activated by integrating MAPa/H2O in both externally and internally into perovskite crystals. MAPa effectively prevents the loss of organic salts and maintains the dispersion of Pb-I framework, preventing the perovskite component loss and decomposition. H2O and organic salts trends to form hydration complexes, which lowers the energy barrier and enhances the reactivity of the humidity-induced Ostwald ripening reaction. These improvements allow the screen-printed perovskite thin films achieve controlled secondary growth and ion exchange, thereby reducing defects and optimizing energy level alignment. The resulting fully screen-printed PSCs exhibits a record power conversion efficiency of 19.47 % and an operational stability over 1,000 h with maintaining 91.6 % of the highest efficiency under continuous light stress at maximum power point.

Tetramethylurea Based Intermediate Phase Engineering for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) are emerging photovoltaic devices renowned for their high efficiency and low cost. Efficient and stable PSCs depend on high-quality perovskite films, which are strongly influenced by the excellent nucleation and growth. The choice of solvent is critical for the crystallization behavior of perovskite films. To improve film quality and address the uncontrollable fast crystallization, it is essential to replace traditional dimethyl sulfoxide (DMSO) solvent. In this work, tetramethylurea (TMU) ligand is successfully introduced into the solvent to replace DMSO for the first time. Through intermediate phase engineering, the crystallization of perovskite films is optimized. The stronger interaction between TMU and solutes versus DMSO can effectively delay the transition from intermediate to perovskite phase, yielding high-quality perovskite films with larger grains and lower defects. Finally, the optimized perovskite films maintained excellent phase stability after aging for 150 h under 95% relative humidity (RH) or at 85 °C, while the device efficiency increased from 19.54% to 21.05%. Furthermore, the devices exhibited outstanding stability after aging for ≈1000 h under 50% RH. This research provides new insights and good example for achieving highly efficient and stable PSCs through intermediate phase engineering.

Siloxane Decorated Water-Obstructing Guest for Efficient Air-Processed OSCs

The future applications of organic solar cells (OSCs) necessitate a thorough consideration of their ambient stability and processability, particularly for large area air-processed engineering, but water-induced degradation of active layer critically restricts its development. To surmount this hurdle, a water-obstructing guest (WOG) strategy is proposed to attenuate the interaction of the active layer with water molecules, reduce defects in blend films, and enhance the devices stability under high relative humidity (RH) conditions by introducing a siloxane-containing polymer D18-SiO. In addition to suppressing trap density, the WOG with hydrophobic and low surface free energy characteristics, forms a capping layer that blocks moisture penetration while preserving ideal nano-micromorphology with high crystallinity and tight packing properties. Power conversion efficiencies (PCE) of >19% is reported for spin coating OSCs fabricated across an RH range of 20 to 90%, and PCE of >17% blade coating OSCs at 90% RH. The D18-SiO, serves as a protective barrier to enhance the device stability, and the corresponding unencapsulated OSCs retained 80.7% of its initial performance in air (≈ 40% RH) after 600-h maximum power point tracking under continuous light illumination, showcasing great potential in designing WOG strategy for large-scale production of air-processed OSCs.

Super Strong Bonding at the Interface between ETL and Perovskite for Robust Flexible Optoelectronic Devices

Organic-inorganic hybrid perovskites have demonstrated great potential for flexible optoelectronic devices due to their superior optoelectronic properties and structural flexibility. However, mechanical deformation-induced cracks at the buried interface and delamination from the substrate severely constrain the optoelectronic performance and device lifespan. Here, we design a two-site bonding strategy aiming to reinforce the mechanical stability of the SnO2/perovskite interface and perovskite layer using a multifunctional organic salt, 4-(trifluoromethoxy)phenylhydrazine hydrochloride (TPH). This approach significantly enhances the bonding at the buried interface between the electron transport layer and perovskite layer, which is demonstrated by TPH-modified SnO2/perovskite interface remaining intact after 10,000 bending cycles. Meanwhile, TPH mitigates void formation, enhances perovskite crystallinity at the buried interface, and inhibits ion migration inside the devices. Furthermore, incorporating TPH in perovskite bulk decreases the nucleation activation energy and accelerates nucleation, leading to high-quality perovskite film. Consequently, power conversion efficiencies (PCEs) of 21.64 % and 23.61 % are achieved for target flexible and rigid perovskite solar cells, respectively. The target flexible device retained 92.3 % of its initial PCE after 25,000 bending cycles. This approach provides a robust solution for enhancing the mechanical durability of flexible perovskite optoelectronic devices.

Nonvolatile and Strongly Coordinating Solvent Enables Blade-coating of Efficient FACs-based Perovskite Solar Cells

Blade-coating has emerges as a critical route for scalable manufacturing of perovskite solar cells. However, the N2 knife-assisted blade-coating process under ambient conditions typically yields inferior-quality perovskite films due to inadequate nucleation control and disorderly rapid crystallization. To address this challenge, a novel solvent engineering strategy is developed through the substitution of N-methyl-2-pyrrolidone (NMP) with 1,3-dimethyl-1,3-diazinan-2-one (DMPU). The unique physicochemical properties of DMPU, characterized by low vapor pressure, strong coordination capability, and limited PbI2 solubility, synergistically regulate nucleation and crystallization kinetics. This enables rapid nucleation, stabilization of intermediate phases in wet films, and controlled crystal growth, ultimately producing phase-pure perovskite films with reduced defect density. Moreover, the feasibility and superiority of the mixed solvent strategy are demonstrated. The optimized blade-coated PSCs achieve a power conversion efficiency of 21.74% with enhanced operational stability, retaining 84% initial efficiency under continuous 1-sun illumination for 1,000 h. This work provides new insights into solvent design for preparing blade-coated perovskite films.

Self-Assembled Charge Bridge Path at the Sn-Pb Perovskite/C60 Interface for High-Efficiency All-Perovskite Tandem Solar Cells

Narrow bandgap mixed tin-lead perovskite solar cells (PSCs) have garnered substantial research interest owing to their remarkable optoelectronic properties. However, non-radiative recombination and carrier transport losses at the interface between the perovskite layer and the charge transport layer (C60) significantly reduce the overall efficiency of mixed tin-lead PSCs. To address this challenge, 9-Fluorenylmethyl carbazate (9FC) is incorporated at the interface between perovskite and C60. The hydrazide group present in 9FC effectively mitigates the oxidation of Sn2+. Furthermore, 9FC can engage in chemical bonding with the perovskite, while the outward-facing aromatic rings create effective π-π interactions with C60, thereby promoting enhanced interfacial charge transfer. The highest-performing mixed tin-lead PSCs achieve a power conversion efficiency (PCE) of 23.97%, accompanied by an impressive open-circuit voltage of 0.91 V. Additionally, these tin-lead PSCs facilitate the development of highly efficient two-terminal and four-terminal all-perovskite tandem solar cells, which demonstrate efficiencies of 27.01% and 28.07%, respectively.

ZnO-Based Photomultiplication-Type Infrared Photodetectors for Ultrasensitive Upconverters

High-sensitivity infrared photodetectors have attracted attention due to their broad applications. Photomultiplication is an ideal choice for high-sensitivity photodetectors since it can generate large photogenerated current under incident faint illumination, making them more user-friendly and cost-effective without any extra amplifier circuits. In this work, 2 wt.% acetic acid in methanol is optimized to treat the electron-accumulated ZnO layer in photodetector ITO/ZnO/PbS/Ag by increasing its interfacial oxygen vacancies, thus the interfacial band bends at the ZnO/PbS interface due to the accumulated charges under illumination. In this way, a high-gain photomultiplication-type photodetector ITO/ZnO/PbS/Ag, in which PbS colloidal quantum dots (CQDs) act as the active layer, is presented. As a result, a high responsivity of 524 A/W with a high external quantum efficiency of 66516% is achieved from the photodetector ITO/ZnO/PbS/Ag under 0.2 µW cm-2 980 nm illumination at -1 V. Further, a low turn-on voltage of 2 V is obtained from the upconverters ITO/ZnO/PbS(240 nm)/TAPC(50 nm)/CBP:Ir(ppy)3(60 nm)/BCP(20 nm)/LiF(1nm)/Al under 1.637 mW cm-2 980 nm illumination, exhibiting a photon-to-photon conversion efficiency of 11.08%. In addition, upconversion imaging through a single-pixel device and a 16 × 16 display array is demonstrated, implying its potential scalable applications. Therefore, it provides a promising and applicable pathway for high-performance upconverters.

Minute-Level Room-Temperature Switching and Long Cycle Stability of Thermochromic Inorganic Perovskite Smart Windows

Perovskite smart windows (PSWs) are widely investigated owing to excellent thermochromic properties, while restricted by poor transition performance and cycle stability. Herein, dimethyl sulfoxide vapor is utilized as an induction reagent for rapid reversible switching at room temperature between the colored and bleached phases. To obtain PSWs with different optical properties and transition performance, red CsPbIBr2, yellow Rb0.5Cs0.5PbIBr2 and brown CsSn0.1Pb0.9IBr2 are prepared through alloying. The perovskites can exhibit reversible switching at 27.4-34.3 °C within 1.9-5.1 min. Even after 100 cycles, they exhibit remarkable stability of luminous transmittance (retention ≥97.4%) and transition time (retention ≥97.6%). Experimental characterization proves that the reversible switching occurs between colored three-dimension perovskite phase and bleached zero-dimension perovskite phase. In the field test (air temperature = 21.6-26.5 °C), model houses with PSWs exhibit a maximum indoor temperature drop of 4.2 °C. Furthermore, they exhibit considerable temperature modulation ability up to 7.9 °C under a solar simulator (temperature of the control model house = 60 °C). The decrease in the luminous transmittance of the PSWs after 20 days is 2.9%, indicating excellent long-term stability. This study offers PSWs with prominent transition performance and long cycle stability.

Perovskite Crystallization Regulation by a Green Antisolvent for High-Performance NiOx-Based Inverted Solar Cells

Environmentally friendly antisolvents are key to achieving efficient, reproducible, and sustainable perovskite solar cells (PSCs). Here, a comparison was made between the traditional highly toxic chlorobenzene (CB) antisolvent and green antisolvents ethyl acetate (EA) and dimethyl carbonate (DMC). The employment of green antisolvent DMC was shown to result in the formation of perovskite films with enhanced grain size and superior crystal quality. This leads to an optimal energy level alignment with the electron transport layer, effectively mitigating the nonradiative recombination caused by film imperfections, reducing the loss of organic components during the annealing process, and suppressing the formation of the lead iodide phase. Finally, the champion device, based on the antisolvent DMC, exhibited a high power conversion efficiency (PCE) of 25.18%, which is one of the high PCEs reported for this device structure. Moreover, the device maintains 92% of its original PCE after approximately 1000 h under environmental conditions.

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.

Interfacial seed-assisted FAPbI3 crystallization and phase stabilization enhance the performance of all-air-processed perovskite solar cells

Formamidinium lead triiodide (FAPbI3) has received significant attention in the field of perovskite solar cells (PSCs) owing to its excellent optoelectronic properties and high thermal stability. However, the photoactive α-FAPbI3 perovskites are highly susceptible to degradation into non-perovskite δ-FAPbI3 phases, especially under humid conditions, which severely diminishes the device performance of FAPbI3 PSCs. Here, we propose an interfacial seeding strategy for regulating crystallization and stabilizing α-FAPbI3 perovskites in humid air. By post-treating an antisolvent-free, air-processed perovskite wet film with inorganic cesium lead triiodide (CsPbI3) nanocrystals, a functional seed layer is formed that effectively mitigates the erosion by humid air while facilitating the conversion of intermediates to the α-FAPbI3 phase. The interfacial seed-modified FAPbI3 perovskite films exhibit improved crystal quality and denser morphology. As a result, the efficiency of all-air-processed carbon-based PSCs is improved from 15.90% for the control to 18.04%. In addition, the unencapsulated PSCs based on interfacial seed-modified FAPbI3 films show improved environmental stability compared to their control counterparts, maintaining 80% of their initial efficiency after 60 days.

Idealizing Air-Processed Perovskite Film Competitive by Surface Lattice Etching-Reconstruction for High-Efficiency Solar Cells

Air-processed perovskite solar cells are desirable for the large-scale manufacturing application in the future, yet the presence of moisture and oxygen goes against perovskite crystallization and deteriorates phase stabilization, leading to the formation of substantial defective nano-impurities, especially on the vulnerable surface. Here, we propose a strategy to simultaneously remove superficial defect layer and solidify the surface by soaking air-fabricated perovskite film into low-polar organic esters at elevated temperature to trigger an in situ dynamic surface lattice disassemble and reconstruction process. Molecular dynamics simulations and experimental results indicate that the inorganic CsPbI2Br perovskite is first dissolved and then the Br-rich phase is recrystallized at solid-liquid interface owing to the balance between weak solubility and high-temperature induced annealing process, thus hardening the soft surface and releasing the lattice tensile stress, which benefits the minimization of interfacial recombination and improvement of the structural stability. As a result, we prepare a carbon-based CsPbI2Br device in complete air without precise control on humidity, achieving a champion efficiency of 15.37 % with excellent resistance to harsh attackers. This method offers a promising avenue for overcoming the limit of processing conditions on advancing perovskite-based optoelectronic devices.

Boosting Photovoltaic Efficiency: The Role of Functional Group Distribution in Perovskite Film Passivation

The utilization of small organic molecules with appropriate functional groups and geometric configurations for surface passivation is essential for achieving efficient and stable perovskite solar cells (PSCs). In this study, two isomers, 4-sulfonamidobenzoic acid (4-SA) and 3-sulfamobenzoic acid (3-SA), both featuring sulfanilamide and carboxyl functional groups arranged in different positions, are evaluated for their effectiveness in passivating defects of the perovskite layer. The calculation and characterization results reveal that 3-SA, with its meta-substitution, offered superior passivation compared to the para-substituted 4-SA, leading to enhanced charge carrier dynamics and extraction efficiency. The devices treated with 3-SA demonstrates a notable increase in power conversion efficiency from 21.50% to 23.30%. Moreover, these devices maintain over 90% of their initial efficiency after 2000 h in a 30% relative humidity environment, showcasing exceptional long-term stability. This research advances strategic design approaches for small molecule passivation, providing critical insights for the enhancement of perovskite optoelectronic applications.

Improving Performance of Perovskite Solar Cells by Reducing Energetic Disorder of Hole Transport Polymer

Polymer hole transport materials offer significant efficiency and stability advantages for p-i-n perovskite solar cells. However, the energetic disorder of amorphous polymer hole transport materials not only limits carrier transport but also impedes contact between the polymer and perovskite, hindering the formation of high crystalline quality perovskites. Herein, a novel low energetic disordered polymer hole transport material, PF8ICz, featuring an indeno[3,2-b]carbazole unit with extended π-conjugation is designed and synthesized. Analyses based on both theoretical calculations and experimental validation highlight the advantages of PF8ICz as a low energetic disorder polymer hole transport material for perovskite solar cells, including improved carrier transport, enhanced perovskite affinity/passivation, and optimized energy levels. Perovskite films formed atop PF8ICz exhibit superior crystalline quality and improved exciton dynamics. PF8ICz-based perovskite solar cells achieve remarkable power efficiency (PCE > 25.4%) and outstanding stability (retaining 96.2% and 95.0% of their PCE under the ISOS-D-3 and ISOS-L-3 protocols over 1000 h, respectively). These findings underscore the importance of rational design of hole transport materials, contributing to the development of high-performance, stable perovskite solar cells for sustainable energy solutions.

Solvent-Mediated Growth of a Hierarchical Zero-Dimensional Architecture for Efficient CsPbI3 Quantum Dot Solar Cells

Perovskite quantum dots (QDs) are promising optoelectronic materials. The large surface area provides an opportunity for ligand engineering to protect the QDs, while also impeding the charge transport in the QD array. Here, the solvent-mediated growth of a hierarchical zero-dimensional (HZD) architecture between CsPbI3 QDs is reported. The HZD architecture is grown on the CsPbI3 QD film through a feasible method rather than introducing intricate molecules into the CsPbI3 QD solution. Acetonitrile solvent with high polarity strips lead iodide from the QD surface, and then the lead iodide reacts with the phenethylamine iodide to form HZD architecture. The HZD architecture acts as a "charge bridge" to enhance the coupling between CsPbI3 QDs, resulting in improved photoelectric properties. As a result, the optimized device achieves a high-power conversion efficiency of 15.4%, remarkably higher than the 14% of the control device. This work demonstrates the significance of surface chemistry for perovskite QDs and provides a feasible strategy for realizing high-performance perovskite QDs-based optoelectronic devices.

Multistage Regulation Strategy via Fluorine-Rich Small Molecules for Realizing High-Performance Perovskite Solar Cells

Perovskite solar cells (PSCs) are an ideal candidate for next-generation photovoltaic applications but face many challenges for their wider application, including uncontrolled fast crystallization, trap-assisted nonradiative recombination, and inefficient charge transport. Herein, a multistage regulation (MSR) strategy for addressing these challenges is proposed via the introduction of fluorine-rich small molecules with multiple active points (i.e., 1-[Bis(trifluoromethanesulfonyl)methyl]- 2,3,4,5,6-pentafluorobenzene (TFSP)) into the precursor solution of the perovskite film. The addition of TFSP effectively delays and regulates the crystallization and growth process of the perovskite film for larger grains and fewer defects, and it effectively improves the coverage of self-assembled molecules for efficient charge transport. The multiple active points of TFSP induce a strong binding affinity with uncoordinated defects in the perovskite film. Moreover, the high fluorine content of TFSP induces strong electronegativity to establish a high binding strength between the perovskite film and electron transport layer. Finally, PSCs prepared by the MSR strategy demonstrated an optimal power conversion efficiency (PCE) of 25.46% and maintained 91.16% of the initial PCE under nonpackaged air conditions and at a relative humidity of 45% after 3000 h.

Strategic Integration of Machine Learning in the Design of Excellent Hybrid Perovskite Solar Cells

The photoelectric conversion efficiency (PCE) of perovskites remains beneath the Shockley-Queisser limit, despite its significant potential for solar cell applications. The present focus is on investigating potential multicomponent perovskite candidates, particularly on the application of machine learning to expedite band gap screening. To efficiently identify high-performance perovskites, we utilized a data set of 1346 hybrid organic-inorganic perovskites and employed 11 machine learning models, including decision trees, convolutional neural networks (CNNs), and graph neural networks (GNNs). Four descriptors were utilized for high-throughput screening: sine matrix, Ewald sum matrix, atom-centered symmetry functions (ACSF), and many-body tensor representation (MBTR). The results indicated that LightGBM and CatBoost somewhat surpassed XGBoost in decision tree models, but random forests lagged. Among the CNN models utilizing the same four descriptors, CustomCNN and VGG16 surpassed Xception, while EfficientNetV2B0 exhibited the least favorable performance. When the sine matrix and Ewald sum matrix served as adjacency matrices in GNN models, GCSConv exhibited a considerable improvement over GATConv and a slight advantage over GCNConv. Significantly, GCSConv outperformed other models when utilized with the Ewald sum matrix. The ideal combination of descriptors and algorithms identified was MBTR + CustomCNN, with an R2 of 0.94. Subsequently, three perovskites exhibiting appropriate Heyd-Scuseria-Ernzerhof (HSE06) band gaps were identified to define the defects. Among them, CH3C(NH2)2SnI3 exhibited superior performance in both vacancy and substitutional defects compared to C3H8NSnI3 and (CH3)2NH2SnI3. This high-throughput screening method with machine learning establishes a robust foundation for selecting solar materials with exceptional photoelectric properties.

Removal of Residual Additive Enabling Perfect Crystallization of Photovoltaic Perovskites

Achieving high-efficiency perovskite solar cells (PSCs) hinges on the precise control of the perovskite film crystallization process, often improved by the inclusion of additives. While dimethyl sulfoxide (DMSO) is traditionally used to manage this process, its removal from the films is problematic. In this work, methyl phenyl sulfoxide (MPSO) was employed instead of DMSO to slow the crystallization rate, as MPSO is more easily removed from the perovskite structure. The electron delocalization associated with the benzene ring in MPSO decreases the electron density around the oxygen atom in the sulfoxide group, thus reducing its interaction with PbI2. This strategy not only sustains the formation of a crystallization-slowing intermediate phase but also simplifies the elimination of the additive. Consequently, the optimized PSCs achieved a leading power conversion efficiency (PCE) of 25.95 % along with exceptional stability. This strategy provides a novel method for fine-tuning perovskite crystallization to enhance the overall performance of photovoltaic devices.

Mesoporous structured MoS2 as an electron transport layer for efficient and stable perovskite solar cells

Mesoporous structured electron transport layers (ETLs) in perovskite solar cells (PSCs) have an increased surface contact with the perovskite layer, enabling effective charge separation and extraction, and high-efficiency devices. However, the most widely used ETL material in PSCs, TiO2, requires a sintering temperature of more than 500 °C and undergoes photocatalytic reaction under incident illumination that limits operational stability. Recent efforts have focused on finding alternative ETL materials, such as SnO2. Here we propose mesoporous MoS2 as an efficient and stable ETL material. The MoS2 interlayer increases the surface contact area with the adjacent perovskite layer, improving charge transfer dynamics between the two layers. In addition, the matching between the MoS2 and the perovskite lattices facilitates preferential growth of perovskite crystals with low residual strain, compared with TiO2. Using mesoporous structured MoS2 as ETL, we obtain PSCs with 25.7% (0.08 cm2, certified 25.4%) and 22.4% (1.00 cm2) efficiencies. Under continuous illumination, our cell remains stable for more than 2,000 h, demonstrating improved photostability with respect to TiO2.

Self-Sacrificed Additive in Preparing PbI2 Film Enables the Oriented Growth of Perovskite Crystals for Improved Solar Cell Performance

Due to the limitation of the diffusion kinetics of organic amine salts on the PbI2 layer in the two-step method, prepared perovskite particles are small in size, have many defects, and are randomly oriented, and the cell efficiency and stability are difficult to guarantee due to PbI2 residues. Here, we added a volatile additive, N,N,N',N'-tetramethylethylenediamine (TMEDA), to the PbI2 precursor solution and formed preaggregated atomic clusters with PbI2 through TMEDA, which reduced the Gibbs free energy of nucleation to obtain a porous PbI2 layer, and finally obtained a perovskite film with large particles, few defects, ideal crystal plane orientation, and no additive residues. The results show that the photoelectric conversion efficiency of the optimized device is increased by 1.68% (from 21.68% to 23.36%), and the unpackaged optimized device still maintains the maximum efficiency of 77% after being placed in the air for 1200 h. This study provides an effective way to fabricate efficient and stable perovskite solar cells by promoting the nucleation-induced crystallization orientation by volatile additives.