Chen Weijie

Publication date: 16 April 2025

Source: Joule, Volume 9, Issue 4

Author(s): Tianfei Xu, Shengzhong Liu, Sang Il Seok, Wanchun Xiang

Publication date: 16 April 2025

Source: Joule, Volume 9, Issue 4

Author(s): Mingyu Li, Jun Yan, Afei Zhang, Xinzhao Zhao, Xuke Yang, Shuwen Yan, Ning Ma, Tianjun Ma, Dingfu Luo, Zhenhua Chen, Luying Li, Xiong Li, Chao Chen, Haisheng Song, Jiang Tang

Publication date: 16 April 2025

Source: Joule, Volume 9, Issue 4

Author(s): Zhou Xing, Suxiang Ma, Bin-Wen Chen, Mingwei An, Ajuan Fan, Xinqiong Hu, Yang Wang, Lin-Long Deng, Qiufeng Huang, Hiroyuki Kanda, Fahad Gallab Al-Amri, Gainluca Pozzi, Yi Zhang, Jianxing Xia, Jiazhen Wu, Xugang Guo, Mohammad Khaja Nazeeruddin

Multiple functional groups of potassium benzyl(trifluoro)borate (BnBF₃K) are employed as a bifacial linker to improve adhesion and stability in flexible perovskite solar modules. BnBF₃K enhances efficiency to 21.82% (certified at 21.39%) at an area of 12.80 cm² with excellent mechanical flexibility, maintaining 96.56% of initial efficiency after 6000 bending cycles.

Abstract

Flexible perovskite solar cells offer significant potential for portable electronics due to their exceptional power density. However, the commercialization of these devices is hampered by challenges related to mechanical flexibility, primarily due to inadequate adhesion between the perovskite absorber layer and the flexible substrate. Herein, this delamination issue is addressed by employing a bifacial linker, potassium benzyl(trifluoro)borate (BnBF₃K), to enhance adhesion at the SnO₂/perovskite interface. This approach not only improves the mechanical stability of flexible perovskite devices but also reduces buried surface defects and optimizes energy level alignment. Consequently, a record efficiency of 21.82% (certified at 21.39%) is achieved for a flexible perovskite solar module with an area of 12.80 cm² and a high efficiency of 24.15% for a flexible perovskite solar cell. Furthermore, the flexible modules exhibit outstanding mechanical flexibility, retaining 96.56% of their initial efficiency after 6000 bending cycles, demonstrating their suitability for various practical applications.

Two halogenated volatile solid additives DBB and DFBB selected to improve photovoltaic performance has been systematically studied. Our results demonstrate that the addition of DFBB with a higher electrostatic potential extremum and stronger σ-holes compared to DBB can regulate the multi-scale morphology to achieve a superior efficiency of 19.2 % for PM6 : L8-BO and 19.8 % for D18 : L8-BO. This work provides valuable insights to develop volatile additives for high performance OSCs.

Abstract

The incorporation of volatile solid additives has emerged as an effective strategy for enhancing the performance of organic solar cells (OSCs). However, the influence of the electronic structure of these additives on morphological evolution remains insufficiently understood. Herein, 1,4-Dibromobenzene (DBB) and 1,4-Difluoro-2,5-dibromobenzene (DFBB) are introduced as volatile additives into OSCs. Theoretical calculations indicate that DFBB has a higher electrostatic potential extremum and stronger σ-holes interaction compared to DBB, enabling more robust intermolecular interactions with acceptors. The synergistic halogen interactions between DFBB and the active layer matrix balances the differences in crystallinity between the donor and acceptor during the film formation process, promotes the formation of dense molecular packing and ordered orientation, optimizes the vertical composition distribution, and promotes the formation of domain sizes close to the exciton diffusion distance. Consequently, the PM6 : L8-BO-based device treated with DFBB achieves an efficiency of 19.2 % with a fill factor (FF) of 80.8 %, which is superior to the control and DBB. Further validation across various systems, including PM6 : Y6, PM6 : BTP-eC9, and D18 : L8-BO, highlights similar efficiency enhancements, with the D18 : L8-BO system achieving an outstanding PCE of 19.8 %. This work demonstrates that the modulation of σ-hole interactions in volatile additives can effectively optimize multi-scale morphology for high-performance OSCs.

Nature Communications, Published online: 14 February 2025; doi:10.1038/s41467-025-56060-0

Nature Photonics, Published online: 14 February 2025; doi:10.1038/s41566-025-01616-1

This study enhances nucleation and crystallization in blade-coated perovskite solar cells through the incorporation of two ionic liquids, IH-imidazole acetate and 1-butyl-3-methylimidazolium tetrafluoroborate, into the precursor solution. This method enhances the interaction between the cation group and the Pb-I framework, and leads to uniform, high-quality α-perovskite films. The resulting blade-coated p-i-n device achieves 21.31% efficiency for 1.68 eV wide-bandgap perovskites.

Abstract

Transforming perovskite solar cells into commercial production requires advanced scalable deposition technology. However, the deposition of high-quality perovskite thin films using the blade coating method presents challenges, especially in controlling the nucleation and crystallization of perovskite. In this work, an effective approach is proposed for controlling nucleation and crystallization by simultaneously incorporating two kinds of ionic liquid, namely 1H-imidazole acetate (IMAc), and 1-buty-3-methylimidazolium tetrafluoroborate (BMIMBF₄), into the precursor solution. This innovative strategy initiates π–π interactions between IM and BMIM cations, thereby enhancing the interaction between cations and the Pb-I framework. The competitive mechanism of interaction with Pb-I framework effectively suppresses the formation of unfavorable mesophase, thereby enabling a single crystallization pathway from NMP + PbI₂ to α-perovskite. Consequently, this method effectively reduces defects and enhances the crystal quality of α-perovskite film. Based on this strategy, the power conversion efficiency of the p-i-n wide bandgap perovskite device prepared by the blade coating method, is increased to 21.31%, representing one of the highest efficiencies achieved with this technology for 1.68 eV bandgap FACs-based perovskites. Thus, this approach emerges as a feasible breakthrough strategy that may unleash the full potential of perovskite solar cells.

By employing an inorganic halide as a nanoscale inorganic barrier covering grain boundaries, key challenges in perovskite technology, including defect passivation and halide segregation are addressed. This barrier impressively enhanced the performance and stability of wide-bandgap single-junction perovskite solar cells, with a remarkable fill factor of 84.82% and open-circuit voltage of 1.305 V, resulting in high efficiencies across various bandgaps: 21.54% for 1.70 eV, 20.45% for 1.77 eV, and 19.22% for 1.82 eV. In addition, monolithic all-perovskite tandem solar cells with improved stability and efficiency are demonstrated.

Abstract

Wide-bandgap (WBG) perovskite solar cells (PSCs) play a crucial role in advancing perovskite-based tandem solar cells. In WBG perovskite films, grain boundary (GB) defects are the main contributors to open-circuit voltage (V _OC) deficits and performance degradation. This report presents an effective strategy for passivating GBs by incorporating an inorganic protective layer and reducing the density of GBs in perovskite films. This is achieved by integrating potassium thiocyanate (KSCN) into I-Br mixed halide WBG perovskites. It is reported for the first time that the incorporation of KSCN creates band-shaped barriers along the GBs. In addition, KSCN enlarges the grains of perovskite film. Elemental and structural analyses reveal that these barriers are composed of potassium lead halide. Incorporating KSCN significantly enhances the fill factor and V _OC of WBG single-junction PSCs by reducing trap density. This results in high power conversion efficiencies of 19.22% (bandgap of 1.82 eV), 20.45% (1.78 eV), and 21.54% (1.70 eV) with a C₆₀/bathocuproine electron transport layer, and 18.51% (1.82 eV) with a C₆₀/SnO₂. Furthermore, both operational and shelf stabilities are significantly improved due to reduced light-induced halide segregation. By using inorganic-halide-passivated WBG sub-cells, a monolithic all-perovskite tandem solar cell with an efficiency of 27.04% is demonstrated.

Publication date: 19 February 2025

Source: Joule, Volume 9, Issue 2

Author(s): Jacob J. Cordell, Michael Woodhouse, Emily L. Warren

In this study, the relationship between the configuration of the studied amino pyridine derivatives and their passivation effects has been meticulously investigated to enhance the electrical properties of perovskite surfaces, which enable the inverted FA_1-xCs_xPbI₃ PSC to yield an encouraging efficiency of 25.65% (certified 25.45%, certified steady-state efficiency 25.06%) with the tailored 3-(2-aminoethyl)pyridine (3-PyEA) surface passivator.

Abstract

Formamidinium-cesium lead triiodide (FA_1-xCs_xPbI₃) 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 FA_1-xCs_xPbI₃ 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 (V_I and I₂) through its strong coordination with N_pyridine. 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 (V_FA), 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 FA_1-xCs_xPbI₃ 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.

Herein, an all-in-one additive AMPH is proposed, which can not only function as a reducing agent to suppress Sn⁴⁺ formation, but also can slow down the crystallization and enhance oxidation resistance of Sn-Pb films. This advancement enables 23.07% efficient Sn-Pb perovskite solar cells and 28.73% efficient all-perovskite tandem solar cells with improved operational stability.

Abstract

Hybrid tin-lead (Sn-Pb) perovskites have garnered increasing attention due to their crucial role in all-perovskite tandem cells for surpassing the efficiency limit of single-junction solar cells. However, the easy oxidation of Sn²⁺ and fast crystallization of Sn-based perovskite present significant challenges for achieving high-quality hybrid Sn-Pb perovskite films, thereby limiting the device's performance and stability. Herein, an all-in-one additive, 2-amino-3-mercaptopropanoic acid hydrochloride (AMPH) is proposed, which can function as a reducing agent to suppress the formation of Sn⁴⁺ throughout the film preparation. Furthermore, the strong binding between AMPH and Sn-based precursor significantly slows down the crystallization process, resulting in a high-quality film with enhanced crystallinity. The remaining AMPH and its oxidation products within the film contribute to improves oxidation resistance and a substantial reduction in defect density, specifically Sn vacancies. Benefiting from the multifunctionalities of AMPH, a power conversion efficiency (PCE) of 23.07% is achieved for single-junction narrow-bandgap perovskite solar cells. The best-performing monolithic all-perovskite tandem cell also exhibits a PCE of 28.73% (certified 27.83%), which is among the highest efficiency reported yet. The tandem devices can also retain over 85% of their initial efficiencies after 500 hours of continuous operation at the maximum power point under one-sun illumination.

Organic ammonium salts with varying alkyl chain lengths are used to passivate perovskite surface defects and optimize energy band alignment. Nonylammonium acetate (NAAc) achieves superior passivation through optimal molecular orientation and minimized steric hindrance, leading to 25.79% PCE in inverted PSCs utilizing vacuum flash technology in ambient conditions.

Abstract

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.

Liquid crystal molecule is utilized to promote the movement of solvent complexes under external field, thus amplifying ripening process and optimizing the buried interface. Based on this, the efficiency of device reaches 25.24%, and it still maintains 75% of the original efficiency after 1400 h in a damp heat test.

Abstract

Up to now, post-annealing is most commonly used to post treat the perovskite film to accelerate the ripening process. Nonetheless, the top-down crystallization mechanism impedes the efficient desolvation of solvent complexes. Thus, residual solvent complexes tend to accumulate at the bottom of the film during the ripening process and deteriorate the device. Here, a new strategy with unique concept is promoted to amplify ripening process of perovskite film, in which a nematic thermotropic liquid crystal (LC) molecular is introduced to facilitate the conversion of solvent complexes by utilizing the liquid crystalline behavior under external field. Upon the concurrent application of thermal and force fields, the covalent interaction between LC and solvent complexes generates a driving force, which promotes upward migration of solvent complexes, thereby facilitating their engagement in the ripening process. In addition, the driving force under external fields assists the flattening of grain boundary grooves. Therefore, film quality is improved efficiently with amplified ripening process and adequately handled buried interface. Based on the positive effects, the devices achieve a champion efficiency of 25.24%, and sustained ≈75% of its initial efficiency level even after undergoing a damp heat test (85 °C/85% RH) for 1400 h.

The subsurface of perovskite (PVK) films produced via the solution method exhibits impurities and a high concentration of defects. This paper examines the limitations of conventional post-treatment strategies for regulating the subsurface of PVK films and introduces an innovative pre-treatment strategy aimed at improving the quality of the film subsurface.

Abstract

The subsurface of perovskite (PVK) triggers non-radiative recombination and initiates film degradation due to the impurities and defects. This study investigates the limitations of the conventional surface post-treatment and proposes an innovative pre-treatment strategy to achieve complete impurity elimination and defect passivation of the subsurface. The considerable activity of unannealed PVK films provides a sufficient basis for effective subsurface modification. Following the pre-treatment, the cadmium ions (Cd²⁺) can occupy the lead (Pb) vacancies or substitute lead ions(Pb²⁺), while the introduced ionic ions (I^-) are able to fill the ionic (I) vacancies. The stronger ionic bond between Cd²⁺ and I⁻ helps prevent the loss of I^-, leading to a reduction of defects in film, inhibiting non-radiative recombination and ionic migration at the interface. This innovative strategy successfully eliminates impurities and passivates defects, resulting in a perovskite subsurface characterized by high crystallinity, low defect density, and minimal impurity. These enhancements contribute to enhanced open circuit voltage (V_OC)and fill factor (FF), leading to an impressive power conversion efficiency (PCE) of 24.49%. Notably, after 1600 h of aging in ambient air, the cell retained 87% of its initial performance.

Four quinoxaline-fused-core-based nonfullerene acceptors are synthesized by extending the π-conjugated backbones and halogenated substitution modification. Stronger crystallization and donor–acceptor interactions arising from larger localized dipoles and higher electrostatic potentials, respectively, led to superior blend film morphology, resulting in efficiencies of 18.75% and 19.48% in binary and ternary organic solar cell devices with outstanding thermal stability.

Abstract

Molecular stacking behavior exerts a significant influence on the blend film morphology of organic solar cells (OSCs), further affecting device performance and stability. Modulation of the molecular structure, such as central unit and end-group, can profoundly impact this process. Herein, four quinoxaline (Qx)-fused-core-based non-fullerene acceptors (NFAs), Qx-N4F and Qx-o/m/p-N4F are synthesized combining π-extended end-groups and optimized central units. The isomeric fluorinated central units lead to changes in the local dipole moments and electrostatic potential distribution, which influences the molecular stacking pattern and photoelectronic properties of NFAs. Consequently, binary and ternary devices based on PM6:Qx-p-N4F achieve superior power conversion efficiencies (PCE) of up to 18.75% and 19.48%, respectively. Grazing-incidence wide-angle X-ray scattering (GIWAXS) characterization reveals Qx-p-N4F's stronger crystallinity, aggregation, and donor–acceptor interactions, which can separately enhance short-circuit current density (J _SC) and fill factor (FF) through higher phase purity and tighter molecular stacking based on maintaining more donor–acceptor interfaces. Furthermore, PM6:Qx-p-N4F-based devices demonstrate exceptional thermal stability, retaining 93.2% of the initial PCE value after 3000 h of heating due to the best morphological stability with the most stable stacking structure. These results underscore the significance of synergistic optimization of NFAs through conjugation expansion and halogenation substitution for obtaining efficient and stable OSCs.

This study demonstrates that the incorporation of the multifunctional ionic liquid 1-allyl-3-methylimidazolium dicyanamide into multicomponent perovskite films significantly improves the efficiency and stability of solar cells through precise surface potential homogenization. This strategy achieves an ultra-high power conversion efficiency of 20.44% for wide-bandgap devices (1.81 eV) and increases the efficiency of conventional bandgap devices (1.53 eV) to 25.41%.

Abstract

The synthesis of multicomponent metal halide perovskites (MHPs) by cationic and/or halide alloying allows band gap tuning, optimizing performance and improving stability. However, these multicomponent materials often suffer from compositional, structural, and property inhomogeneities, leading to uneven carrier transport and significant non-radiative recombination losses in lead halide perovskites. While many researchers have focused on the aggregation of perovskite halide ions, the impact of the surface potential has received relatively less attention. In this study, the multifunctional ionic liquid 1-allyl-3-methylimidazole dicyanamide (AMI) is introduced into the perovskite precursor to effectively regulate the surface potential of the perovskite layer. This approach inhibits non-radiative recombination, enhances carrier injection, and improves device performance. Surface potential homogenization within the perovskite layer leads to simultaneous improvements in both the efficiency and stability of perovskite solar cells. For wide-bandgap perovskites (1.81 eV), the optimal power conversion efficiency (PCE) reaches 20.44%, with an open-circuit voltage (V _oc) of 1.339 V, a short-circuit current density (J _sc) of 17.92 mA cm⁻², and a high fill factor (FF) of 85%. This strategy also proved effective for conventional bandgap perovskite solar cells (PSCs) (1.53 eV), leading to a significant increase in performance, with the PCE increasing from 23.22% to 25.41%.

A novel polymeric hole transporter named Poly-DBPP with centrosymmetric biphosphonic acid groups is developed that can anchor to the underlying conductive substrate and interact with the perovskite layer simultaneously. Poly-DBPP improves the efficiencies of blade-coated perovskite solar cells and large-area modules to 25.1% and 22.0%, respectively.

Abstract

Self-assembly monolayer (SAM) hole transporters, consisting of anchoring, spacer, and terminal groups, have played a significant role in the development of inverted perovskite solar cells (PSCs). However, the weak interaction between perovskite and hydrophobic terminal group of SAMs limits surface wettability and interface stability. To address this issue, two novel hole transporters (named DBPP and Poly-DBPP) with centrosymmetric biphosphonic acid groups are developed. Unlike conventional SAM hole transporters, the biphosphonic acid groups in DBPP and Poly-DBPP can anchor to the underlying conductive substrate and interact with the perovskite layer simultaneously, improving surface wettability and suppressing interface recombination. Furthermore, compared to the small-molecular DBPP, Poly-DBPP exhibits higher conductance and excellent uniformity. This translates to a remarkable power conversion efficiency of 25.1% for blade-coated PSCs and 22.0% for large-area modules, respectively. Additionally, the PSCs based on Poly-DBPP demonstrate impressive operational stability, retaining 92% of their initial PCE after 1,600 h of light soaking. This work presents a promising strategy for designing multifunctional hole transporters, paving the way for highly efficient and stable PSCs.

A novel isotropic fullerene-hybridized fused-ring electron acceptor, C₆₀-Y, featuring a high dielectric constant and isotropic molecular packing, has been synthesized. The fullerene hybrid enhances exciton dissociation, reduces energy losses, and improves charge mobility. When incorporated into a ternary blend system, it achieved an impressive PCE of 19.22 %, outperforming other reported ternary OSCs utilizing fullerene derivatives as the third component.

Abstract

A novel isotropic fullerene-hybridized fused-ring electron acceptor, designated C₆₀-Y, has been synthesized via a mild [4+2] Diels–Alder cycloaddition reaction with fullerene C₆₀ to enhance the performance of organic solar cells (OSCs). Comparative analysis shows that C₆₀-Y significantly outperforms the control acceptor Me−Y, with a notable increase in the relative dielectric constant from 2.79 to 3.95. This improvement enhances exciton dissociation and reduces non-radiative energy losses. Additionally, the isotropic molecular packing of C₆₀-Y, similar to fullerene, facilitates efficient interface formation with donor polymers and improves charge mobility. As a result, incorporating C₆₀-Y as an electron acceptor increases the power conversion efficiency (PCE) of binary OSCs to 15.02 %, surpassing the 13.31 % achieved with Me−Y. Moreover, when integrated into a ternary blend system, an impressive PCE of 19.22 % is achieved, top-performing among reported ternary OSCs utilizing fullerene derivatives as the third component. These results suggest that fullerene-hybridized acceptors like C₆₀-Y hold great potential for advancing high-efficiency OSCs by enhancing exciton dissociation, reducing energy losses, and improving charge mobility.

Nature Energy, Published online: 15 November 2024; doi:10.1038/s41560-024-01672-x

This study presents a new modification of bathocuproine (BCP) in perovskite solar cells (PSCs), where the nitrogen atoms are positioned inside the molecule for added stability. This structural adjustment enhances charge transport and device durability. Experimental results show reduced energy losses and improved long-term performance, highlighting the potential of this modified BCP for more efficient and stable PSCs.

Abstract

Along with the growing popularity of the p-i-n structure, bathocuproine (BCP) is increasingly recognized as a crucial buffer layer between the electron transport layer and electrode with the role of mitigating Schottky contact and enhancing performance. However, the chemical structure and role of its functional groups have not been thoroughly elucidated. This study introduces a novel modification of BCP in perovskite solar cells (PSCs) by altering functional groups to optimize their geometrical molecular structures and electronic properties. The substitution of aromatic phenyl and p-tolyl groups to 2,9-position on the BCP is highly effective in increasing the planarity of the conjugated backbone and protecting the reactive nitrogen atoms of the phenanthroline core, thereby improving charge transport and device stability. Experimental analyses, including electrostatic force microscopy, impedance spectroscopy, and photoluminescence, reveal that the modified BCP significantly enhances charge transport, reduces recombination losses, and markedly improves the structural stability of PSCs, leading to prolonged device lifetimes. The findings highlight the potential of structurally optimized BCP derivatives as a critical component in advancing high-efficiency and durable PSCs.

Are tandem solar cells truly hysteresis-free? This study reveals that mobile ions in Si/perovskite and all-perovskite TSCs cause efficiency losses and hysteresis, especially at fast scan rates. Subcell current-voltage characterization quantifies ionic losses in specific subcells and demonstrates the dominant impact of these losses for degradation, particularly in the wide-bandgap subcell. These findings offer key insights for improving long-term stability.

Abstract

The stability of perovskite-based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all-perovskite TSCs using scan-rate-dependent current–voltage (J–V) measurements with drift-diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion-freeze power conversion efficiency from >31% for Si/perovskite and >30% for all-perovskite tandems to ≈28% in steady-state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s⁻¹), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all-perovskite tandems, subcell-dominated J–V characterization reveals more pronounced ionic losses in the wide-bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite-based TSCs which helps to separate ion migration-related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability.

A surface modifier 4-(trifluoromethyl)benzhydrazide (TFH) is reported to construct a reductive chemical environment on the surface of perovskite films and protect them from erosion. TFH anchors onto the Sn-Pb perovskites in a preferred vertical orientation through dual-site binding, forming interface dipoles that facilitate charge extraction. Consequently, a PCE of 28.17% in all-perovskite tandem solar cells is demonstrated.

Abstract

All-perovskite tandem solar cells (TSCs) are gaining increasing attention due to their potential to surpass the efficiency limit of single-junction solar cells. However, as the bottom low-bandgap subcells, tin-lead (Sn-Pb) perovskites suffer from severe nonradiative recombination at the interfaces due to their susceptibility to oxidation and poor crystalline morphology. Here a surface modifier 4-(trifluoromethyl)benzhydrazide (TFH) is reported to construct a reductive chemical environment on the surface of perovskite films and protect them from water and oxygen erosion. TFH anchors onto the Sn-Pb perovskites in a preferred vertical orientation through dual-site binding, forming interface dipoles that facilitate charge extraction. The reductive hydrazine groups of TFH can effectively inhibit the oxidation of Sn²⁺ and I⁻, thereby reducing the defect density and energy disorder of Sn─Pb perovskites. Consequently, the TFH-treated devices achieved a champion PCE of 22.88%, maintaining over 93% of the initial efficiency after continuous one-sun illumination for 500 h. Combined with a 1.79 eV wide-bandgap subcell, it has demonstrated a PCE of 28.17% in all-perovskite TSCs.

A Cs─I bond weakening approach is proposed to realize low-temperature crystalized CsPbI₃ through SMCl introduction. SMCl will interact with CsI and weaken Cs─I bond to dissociate free I⁻ ions, thus promoting [PbI₆]⁴⁻ formation and CsPbI₃ crystallization. As a result, black CsPbI₃ is obtained at 90 °C and flexible CsPbI₃ PSCs are realized with efficiency of 13.86% and good thermal or mechanical stability.

Abstract

All-inorganic triiodide cesium lead (CsPbI₃) exhibits huge potential in perovskite solar cells (PSCs). However, the high-temperature crystallization process (≈340 or 180 °C) limits their further development, especially in flexible PSCs. Here, a Cs─I bond weakening approach is proposed to realize the low-temperature crystallization of CsPbI₃ by introducing organic sulfonate of 1-propylsulfonate-3-methylimidazolium chloride (SMCl). SMCl can strongly interact with CsI and weaken the Cs─I bond to dissociate free I⁻ ions for the effective transition of initial PbI₂ to [PbI₆]⁴⁻, which greatly decreases the crystallization temperature of black CsPbI₃ to 90 °C. As a result, flexible PSCs are realized with efficiency of 13.86%, which is the highest efficiency of flexible CsPbI₃ devices. Besides, SMCl will also help to release the tensile strain and stabilize CsPbI₃ phase, leading to good thermal and mechanical stability. Almost no efficiency loss is observed in flexible PSCs after 36000 bending cycles with a curvature radius of 5 mm.