Hot-Carrier Cooling Regulation for Mixed Sn-Pb Perovskite Solar Cells

Additive Engineering Toward Suppression of Sn2+ Oxidation in Sn-Pb Perovskite Solar Cells: Mechanisms, Advances, and Outlook

Inorganic hybrid tin-lead mixed perovskite solar cells (Sn-Pb PSCs) have attracted widespread attention in virtues of adjustable/narrow bandgaps, low toxicity, and application prospects in all-perovskite tandem solar cells, and the recorded power conversion efficiency (PCE) has reached 24.1%. However, the easy oxidation of Sn2+ brings about abundant Sn vacancies and high concentrations of p-type self-doping, leading to the efficiency and durability of Sn-Pb PSCs still lagging behind those of Pb-based counterparts. To inhibit the oxidation of Sn2+, feasible additive engineering is proposed and shows impressive effects. Herein, the recent research progress about additive engineering for Pb-Sn PSCs in depth is discussed and reviewed. The additive molecules are classified into antioxidant additives, reducing additives, and competitive additives, according to different action objects, namely Sn2+, Sn4+, and oxygen. Meanwhile, the corresponding functional groups, antioxidant properties, the effect on optoelectronic performances of the device, as well as underlying mechanisms are systematically summarized. Finally, an outlook is provided for future directions in additive engineering toward the suppression of Sn2+ oxidation in Sn-Pb perovskites.

Synergistic bimolecular erosion-healing interfacial passivation for wide-bandgap perovskite and tandem solar cells

All-perovskite tandem solar cells present immense potential due to their exceptional performance and versatility. However, their practical implementation is impeded by significant challenges, particularly in large-area devices, where interfacial inhomogeneities in wide-bandgap (WBG) perovskite subcells lead to high open-circuit voltage losses and low fill factors. Here, we introduce a synergistic bimolecular corroding-healing passivation strategy to enhance WBG perovskite films' passivation and interfacial uniformity. Unlike conventional passivation methods relying on halide ammonium salts, this approach directly employs precursor diamines to passivate interfacial defects, suppress recombination, and crucially induce mild surface corrosion, creating random openings on the perovskite surface. Paired molecules of piperazinium iodide then penetrate these openings, enabling deeper defect passivation and surface healing to form a smooth, homogeneous interface. This strategy enabled 1.78 eV WBG perovskite solar cells to achieve a power conversion efficiency (PCE) of 20.47% with an ultrahigh fill factor of 85.10%. Furthermore, when integrated with narrow-bandgap perovskite subcells, the fabricated all-perovskite tandem solar cells delivered PCEs of 28.36% (0.07 cm2) and 27.52% (1.02 cm2). This dual-molecular erosion-healing passivation strategy offers an effective and scalable solution to optimize the perovskite interface, driving advancements in the performance and manufacturability of WBG perovskite and tandem solar cells.

Synergistic Strategy of Anion and Cation at the SnO2/Perovskite Interface Constructing Efficient and Stable Solar Cells

The chemical regulation of SnO2 to enhance the properties of the buried interface in perovskite films is extensively investigated, but the underpinning mechanisms remain insufficiently understood. In this study, a synergistic strategy for cation fixation and anion diffusion by incorporating (3-amino-3-carboxypropyl) dimethylsulfonium chloride (Vitamin U, VU) into a SnO2 colloidal solution is proposed. The cationic end (─COOH, ─NH2) of VU effectively inhibits the aggregation of SnO2 particles and promotes electron extraction and transport via chemical interactions. Simultaneously, the anionic end (Cl⁻) acts to eliminate surface hydroxyl groups on SnO2 and occupy oxygen vacancies. Crucially, a novel direct current polarization test is employed to elucidate the migration mechanism of Cl⁻, revealing that the migration principle of chloride ions in SnO2, and chloride ions can penetrate to the bottom of the perovskite layer, forming a wide bandgap thin layer that aids in energy level alignment and regulates charge transfer behavior. Ultimately, the device based on VU-modified SnO2 achieves a champion efficiency of 25.27%. Moreover, it demonstrates impressive storage stability with a T90 of 5770 h and retains 86% of its initial efficiency after 1110 h of continuous light exposure.

Interfacial Dipole-Induced High Open-Circuit Voltage for Efficient Perovskite Solar Cells

Solution-processed perovskite films frequently exhibit a high density of defects at their surfaces and grain boundaries, leading to significant nonradiative recombination, hysteresis, and energy losses. Interfacial modification is a crucial strategy for enhancing the photovoltaic performance of perovskite solar cells. In this study, we introduce a polar molecule 3,3,3-trifluoropropionamide (TFAN) with a permanent dipole moment to modify the surface of perovskite films, effectively passivating the uncoordinated Pb2+. The results demonstrate that appropriate interfacial modifications can significantly reduce trap state density and suppress nonradiative recombination, thereby facilitating efficient charge transfer. Without sacrificing photocurrent, the efficiency of TFAN-modified perovskite films increased from 22.21% to 25.17%, while the open-circuit voltage rose from 1.14 to 1.23 V. These enhancements substantially improved the photovoltaic parameters and greatly enhanced operational stability.

Competitive-Coordination-Induced Crystallization Regulation for Efficient and Stable Sn-Pb Perovskite Solar Cells

The unbalanced crystallization rate between Sn- and Pb-based perovskites leads to their heterogeneous distribution and inferior quality of Sn-Pb perovskite films. The promising strategy of selective molecular interaction would balance the crystallization rate. However, the deeper selectivity mechanism needs to be considered, particularly in terms of the entire coordination reaction in the perovskite precursor solution. Herein, we take advantage of thermodynamics and molecular orbital theory to reveal the competitive coordination of additive, i.e., methyl 5-aminolevulinate hydrochloride (5-AH), with SnI2 and PbI2. The SnI2 competes with PbI2 in coordinating with 5-AH to form the thermodynamically favored SnI2-5-AH adducts with stronger SnI2-Cl-, thereby mediating the crystallization rate of the Sn- and Pb-based perovskite. Such crystallization regulation improves the composition uniformity and crystallization quality, which effectively suppresses nonradiative recombination. Additionally, the strong interaction between Sn2+ and 5-AH as well as reductive grain boundaries inhibits the oxidation of Sn2+. Therefore, the optimal devices with 5-AH exhibit an improved PCE of 23.76% with a high voltage of 0.885 V and long-term stability.

Multi-cation synergy improves crystallization and antioxidation of CsSnBr3for lead-free perovskite light-emitting diodes

Tin (Sn) perovskites have emerged as promising alternatives to address the toxicity concerns associated with lead-based (Pb) perovskite light-emitting diodes (PeLEDs). However, the inherent oxidation of Sn perovskite films leads to a serious efficiency roll-off in PeLEDs at increased current densities. Although three-dimensional CsSnBr3perovskites exhibit decent carrier mobilities and thermal stability, their rapid crystallization during solution processing results in inadequate surface coverage. This inadequate coverage increases non-radiative recombination and leakage current, thereby hindering Sn PeLED performance. Herein, we present a multi-cation synergistic strategy by introducing the organic cations formamidinium (FA+) and thiophene ethylamine (TEA+) into CsSnBr3perovskites. The addition of organic cations delays crystallization by forming hydrogen bonds interacting with the CsSnBr3. The smaller FA+enters the perovskite lattice and improves crystallinity, while the larger TEA+cation enhances surface coverage and passivates defect states. By further optimizing the interface between PEDOT:PSS and perovskite layers through the use of ethanolamine and a thin layer of LiF, we achieved a red Sn-based PeLED with an emission wavelength of 670 nm, a maximum luminance of 151 cd m-2, and an external quantum efficiency of 0.21%.

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.

Universal in situ oxide-based ABX3-structured seeds for templating halide perovskite growth in All-perovskite tandems

Precise control over halide perovskite crystallization is pivotal for realizing efficient solar cells. Here, we introduce a strategy utilizing in-situ-formed oxide-based ABX3-structured seeds to regulate perovskite crystallization and growth. Introducing potassium stannate into perovskite precursors triggers a spontaneous reaction with lead iodide, producing potassium iodide and lead stannate. Potassium iodide effectively passivates defects, while PbSnO3 (ABX3-structured), exhibiting a 98% lattice match, acts as a template and seed. This approach facilitates pre-nucleation cluster formation, preferential grain orientation, and the elimination of intermediate-phase processes in perovskite films. Incorporating potassium stannate into both the perovskite precursors and the buried hole transport layers enables single-junction 1.25 eV-bandgap Sn-Pb perovskite solar cells to achieve a steady-state efficiency of 23.12% and enhanced stability. Furthermore, all-perovskite tandem devices yield efficiencies of 28.12% (two-terminal) and 28.81% (four-terminal). This versatile templating method also boosts the performance of 1.77 eV and 1.54 eV-bandgap cells, underscoring its broad applicability.

Halogen-bond-mediated inhibition of ion migration for stable Sn-Pb perovskite solar cells

The incorporation of perfluorooctane iodides into Sn-Pb perovskite solar cells significantly mitigates performance losses caused by ion migration and the internal field shielding effect, while simultaneously enhancing both device efficiency and stability.

Ten Years of Perovskite Lasers

Over the past decade, semiconducting halide perovskite lasers have emerged as a transformative platform in optoelectronics, owing to unique properties such as high photoluminescence quantum yields, tunable bandgaps, and low-cost fabrication processes. This review systematically examines the advancements in halide perovskite lasers, covering diverse laser architectures, such as whispering gallery mode, Fabry-Pérot, plasmonic, bound states in the continuum (BIC), quantum dot, and polariton lasers. The mechanisms of optical gain, the role of material engineering in optimizing lasing performance, and the challenges associated with continuous-wave (CW) pumping and electrically driven lasing are discussed. Furthermore, recent progress in improving the stability and scalability of perovskite lasers, essential for their integration into practical applications in displays, optical communications, sensing, and integrated photonics is highlighted. Finally, future research directions are discussed, emphasizing the potential of perovskite lasers to revolutionize various technological domains by enabling the development of next-generation photonic devices.

Multifunctional Modification of the Buried Interface in Mixed Tin-Lead Perovskite Solar Cells

Mixed tin-lead perovskite solar cells can reach band gaps as low as 1.2 eV, offering high theoretical efficiency and serving as base materials for all-perovskite tandem solar cells. However, instability and high defect densities at the interfaces, particularly the buried surface, have limited performance improvements. In this work, we present the modification of the bottom perovskite interface with multifunctional hydroxylamine salts. These salts can effectively coordinate the different perovskite components, having critical influences in regulating the crystallization process and passivating defects of varying nature. The surface modification reduced traps at the interface and prevented the formation of excessive lead iodide, enhancing the quality of the films. The modified devices presented fill factors reaching 81 % and efficiencies of up to 23.8 %. The unencapsulated modified devices maintained over 95 % of their initial efficiency after 2000 h of shelf storage.

Flexible Narrow Bandgap Sn-Pb Perovskite Solar Cells with 21% Efficiency Using N,N'-Carbonyldiimidazole Treatments

Flexible tin-lead (Sn-Pb) mixed perovskite solar cells (PSCs) are among the promising flexible photovoltaics, owing to the narrow bandgap (NBG) of Sn-Pb perovskites, flexible and wearable features, and their role as a critical component in all-perovskite tandem photovoltaics. However, the flexible Sn-Pb PSCs suffer from a low power conversion efficiency, no higher than 18.5%, along with limited stability. Herein, we reported an efficient and stable flexible NBG Sn-Pb PSC via an N,N'-carbonyldiimidazole (CDI) passivation strategy. CDI, with strong adsorption energy, preferentially binds to Sn2+ compared with oxygen (O2), thus effectively inhibiting the adsorption of O2 on perovskite surfaces. The transfer of electron density around Sn2+ dramatically decreased, thus suppressing Sn2+ oxidation. The CDI treatments endowed the Sn-Pb mixed films with fewer defects, improved crystallinity, better morphology, and matched energy-level alignment. The flexible Sn-Pb devices exhibited a high PCE of 21.02%. Besides, the devices showed enhanced stability and promoted flexibility. This work provides a pathway to visibly increase the efficiency and stability of the flexible Sn-Pb mixed photovoltaic cells.

Enhanced Electric Field Minimizing Quasi-Fermi Level Splitting Deficit for High-Performance Tin-Lead Perovskite Solar Cells

The quasi-Fermi level splitting (QFLS) deficit caused by the non-radiative recombination at the interface of perovskite/electron transport layer (ETL) can lead to severe open-circuit voltage (VOC) loss and thus decreases the efficiency of perovskite solar cells (PSCs), however, has received limited attention in inverted tin-lead PSCs. Herein, the strategy of constructing an extra-electric field is presented by introducing ferroelectric polymer dipoles (FPD)-β-poly(1,1-difluoroethylene)-to suppress the QFLS deficit. The directional polarization of FPD can enhance the built-in electric field (BEF) and thus promote the charge transfer at the perovskite/ETL interface, which effectively suppresses non-radiative recombination. Furthermore, the incorporation of FPD facilitates high-quality crystallization of perovskite and reduces the surface energetic disorder. Therefore, the QFLS deficit in the perovskite/ETL half-stacked device is reduced from 62 to 27 meV after incorporating FPD, and the optimized device achieves an efficiency of 23.44% with a high VOC of 0.88 V. Additionally, the addition of FPD increases the activation energy for ion migration, which can reduce the effect of ion migration on the long-term stability of the device. Consequently, the FPD-incorporated device retains 88% of the initial efficiency after 1100 h of continuous illumination at the maximum power point (MPP).

Alder-Ene Reaction-Mediated Suppression of Tin(II) Oxidation for Efficient Tin-Lead Perovskite Solar Cells

Despite numerous studies have reported the inhibition of tin (II) oxidation in mixed tin-lead halide perovskite, there remains a dearth of mechanistic information regarding how tin (II) undergoes oxidation in the precursor solution, particularly in terms of the involvement of DMSO. We here take advantage of density functional theory (DFT) to uncover that SnI2 can coordinate with DMSO and react with singlet oxygen, resulting in the generation of Sn (IV). Moreover, our DFT simulations reveal that benzaldehyde oxime (BZHO) competes with SnI2 in reacting with oxygen through the Alder-ene reaction, hence effectively restraining the oxidation of tin (II), which is further verified by several experimental characterizations. Besides, the introduction of BZHO has also regulated the crystallization of the perovskite film and modified the electronic structure of the perovskite surface. As a result, the perovskite solar cells with the addition of BZHO demonstrate superior performance and operational stability, retaining 82 % of the initial PCE under continuous 1-sun illumination for 800 hours. Furthermore, the efficiency of all-perovskite tandem solar cells treated with BZHO reached 26.76 %. Therefore, this work presents a promising strategy for designing high-performance and stable all-perovskite tandem solar cells.

Space-Charge-Limited Current Measurements: A Problematic Technique for Metal Halide Perovskites

Space-charge-limited current (SCLC) measurements play a crucial role in the electrical characterization of semiconductors, particularly for metal halide perovskites. Accurate reporting and analysis of SCLC are essential for gaining meaningful insights into charge transport and defect density in these systems. Unfortunately, performing SCLC measurements on perovskites is complicated by their mixed electronic-ionic conductivity. This complexity led to SCLC data often being incorrectly analyzed using simplified models unsuitable for these materials and reported without essential information about how the measurements were performed. In light of recently published SCLC data, common challenges in using SCLC measurements on perovskite materials are addressed, and solutions are discussed in this paper. The applicability of the often-used analytical models, the overlooked issues related to the mixed ionic-electronic conductivity of perovskites, and the complexity of creating single-carrier devices are investigated using drift-diffusion simulations. Finally, guidelines for more accurate reporting and improved analysis are provided.

Effect of ABX3 site changes on the performance of tin-lead mixed perovskite solar cells

Tin-lead mixed perovskite solar cells (TLMPSCs), with the advantage of approaching the Shockley-Queisser (S-Q) limit for photovoltaic applications, have been rapidly developed and achieved a power conversion efficiency (PCE) of 23.7%. Although the low toxicity of TLMPSCs is conducive to sustainable development, the oxidation of Sn2+ could destroy the perovskite structure easily. Thus, most researchers are devoted to improving the photoelectric performance and stability through additive engineering, interface engineering, device structure optimization, solvent engineering, etc. However, TLMPs with different A-sites and X-sites in the ABX3 model and an optimal ratio of Sn : Pb still need to be investigated; this is the basis of mechanistic analysis. In this paper, we introduce TLMPSCs with different A-sites, X-sites, and Sn-Pb ratios. The mechanism and properties of the cations are analyzed based on the performance of TLMPSCs. Finally, a series of prospects for optimizing ABX3 are put forward, with the hope of attracting the attention and interest of researchers.

Reinforcing 2D Single-Crystal Bi2O2CO3 with Additional Interlayer Carbonates by CO2-Assisted Solid-to-Solid Phase Transition

A facile gaseous CO2 mediated solid-to-solid transformation principle is adopted to insert additional CO3 2- anions into the thin single-crystal nanosheets of Bi2O2CO3, which is built of periodic arrays of intrinsic CO3 2- anions and (Bi2O2)2+ layers. The additional CO3 2- anions create abundant defects. The Bi2O2CO3 nanosheets with rich interlayer CO3 2- exhibit superior electronic properties and charge transfer kinetics than the pristine single-crystal 2D Bi2O2CO3 and display enhanced catalytic activity in photocatalytic CO2 reduction reaction and the photocatalytic oxidative degradation of organic pollutants. This work thus illustrates interlayer engineering as a flexible means to build layered 2D materials with excellent properties.

Advances in Mixed Tin-Lead Narrow-Bandgap Perovskites for Single-Junction and All-Perovskite Tandem Solar Cells

Organic-inorganic metal-halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single-junction PV devices, although lead (Pb)-based perovskite solar cells have achieved 26.1% efficiency, the mixed tin-lead (Sn-Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn-Pb perovskite (with a bandgap tuned to ≈1.2 eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley-Queisser radiative limit for the single-junction devices. The performance of the all-perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, the properties and recent development of state-of-the-art mixed Sn-Pb perovskites and their application in single-junction and all-perovskite tandem solar cells are reviewed. Recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth are highlighted. The authors also provide the perspective and outlook on the challenges and strategies for further development of mixed Sn-Pb perovskites in both efficiency and stability for PV applications.

All-perovskite tandem solar cells: from fundamentals to technological progress

Organic-inorganic perovskite materials have gradually progressed from single-junction solar cells to tandem (double) or even multi-junction (triple-junction) solar cells as all-perovskite tandem solar cells (APTSCs). Perovskites have numerous advantages: (1) tunable optical bandgaps, (2) low-cost, e.g. via solution-processing, inexpensive precursors, and compatibility with many thin-film processing technologies, (3) scalability and lightweight, and (4) eco-friendliness related to low CO2 emission. However, APTSCs face challenges regarding stability caused by Sn2+ oxidation in narrow bandgap perovskites, low performance due to V oc deficit in the wide bandgap range, non-standardisation of charge recombination layers, and challenging thin-film deposition as each layer must be nearly perfectly homogenous. Here, we discuss the fundamentals of APTSCs and technological progress in constructing each layer of the all-perovskite stacks. Furthermore, the theoretical power conversion efficiency (PCE) limitation of APTSCs is discussed using simulations.

Reductive Sn2+ Compensator for Efficient and Stable Sn-Pb Mixed Perovskite Solar Cells

Tin-lead (Sn-Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single-junction solar cells approaching the Shockley-Queisser limit. However, due to the easy oxidation of Sn2+, the efficiency and stability of Sn-Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb-based solar cells. Herein, highly efficient and stable FA0.5MA0.5Pb0.5Sn0.5I0.47Br0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC2O4). SnC2O4 with compensative Sn2+ and reductive oxalate group C2O4 2- effectively passivates the cation and anion defects simultaneously, thereby leading to more n-type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn-Pb mixed perovskite solar cell treated with SnC2O4 achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C2O4 2- effectively suppresses the notorious oxidation of Sn2+, leading to significant enhancement in stability. Particularly, it dramatically improves light stability.