Chen Weijie

The excess hole charge carriers in the FAPbI₃ film accelerate degradation of the film under ambient atmosphere. The degradation route differs depending on the ambient humidity levels: amorphization occurs under relative humidity (RH) 5 ± 3%, hydrate species are formed under RH 35 ± 3%, and phase changes to nonperovskite δ-FAPbI₃ under RH 45%±3%.

Excess charge carriers in metal halide perovskite layer have been known to accelerate degradation of the film and devices to cause poor operational stability of perovskite solar cells (PSCs). While mechanisms for such degradation have been predominantly studied for methylammonium-based perovskites, effects of excess charge carriers and their interplays with other degradation causes are barely studied for widely used formamidinium-based perovskites. Herein, a possible decomposition mechanism of the formamidinium lead tri-iodide (FAPbI₃) perovskite in the presence of excess charge under different humidity levels is investigated. The operating condition with excessive charges is simulated by placing half devices with either electron-transporting layer (ETL) or hole-transporting layer (HTL) under 1 sun illumination. FAPbI₃ in contact with ETL degrades more rapidly than the one with HTL, which is attributed to excess hole charge carriers in the film. Under higher humidity, the synergetic effect of excess charge carriers and humidity is found and thus degradation pathway and kinetics are strongly dependent on the humidity level. The fundamental understanding of degradation pathways for formamidinium perovskites should provide a useful insight toward the development of efficient and operationally stable PSCs toward practical usage.

Reverse of oxidation reaction is introduced in perovskite solution through iodine monobromide (IBr) to inhibit aging and improve the stability of solution. Furthermore, IBr can improve the perovskite crystallization process to increase the crystallinity and manage the halogen anion deficits to reduce defect density. Thereby, the optimal device has an efficiency of 24.05% and exhibits excellent stability.

Solution processability is a prominent advantage for the commercial fabrication of perovskite solar cells (PSCs). However, ionic side reactions can cause perovskite solutions to age, which greatly limits the industrial prospects for reproducible production of PSCs. Herein, the mechanism of underlying halogen anion side reactions is elucidated and an effective scheme for managing halogen anions is proposed. The oxidation of halogen anions is the main factor of solution aging. The addition of iodine monobromide (IBr) stabilizes the precursor solution by promoting the reverse oxidation reaction. Meanwhile, IBr can manage the loss of halogen anion in perovskite layers, effectively reducing the defect density. Moreover, IBr can improve the crystallization process to prepare perovskite films with large-sized grains and high crystallinity. As a result, the IBr-based perovskite solution can be stored for 14 days, the optimal device efficiency (24.05% at 0.09 cm²) and long-term operational stability are far superior to control samples. By this strategy, a large-area perovskite solar module with an efficiency of 19.34% is fabricated on the 6 × 6 cm² substrate. This study is dedicated to providing a strategy for managing halogen anions to inhibit solution aging and improve film quality.

The metal halide octahedron is regarded as the fundamental structural and functional unit of perovskites. However, the impact of octahedral connectivity in perovskites on device performance is not systematically explored. This manuscript provides direct experimental evidence that the existence of non-corner-sharing regions is detrimental to device performance and provides key guidance on how to regulate octahedral connectivity.

Abstract

The metal halide (BX ₆)^4- octahedron, where B represents a metal cation and X represents a halide anion, is regarded as the fundamental structural and functional unit of metal halide perovskites. However, the influence of the way the (BX ₆)⁴⁻ octahedra connect to each other has on the structural stability and optoelectronic properties of metal halide perovskite is still unclear. Here, the octahedral connectivity, including corner-, edge-, and face-sharing, of various Cs_xFA_1-xPbI₃ (0 ≤ x ≤ 0.3) perovskite films is tuned and reliably characterized through compositional and additive engineering, and with ultralow-dose transmission electron microscopy. It is found that the overall solar cell device performance, the charge carrier lifetime, the open-circuit voltage, and the current density–voltage hysteresis are all improved when the films consist of corner-sharing octahedra, and non-corner sharing phases are suppressed, even in films with the same chemical composition. Additionally, it is found that the structural, optoelectronic, and device performance stabilities are similarly enhanced when non-corner-sharing connectivities are suppressed. This approach, combining macroscopic device tests and microscopic material characterization, provides a powerful tool enabling a thorough understanding of the impact of octahedral connectivity on device performance, and opens a new parameter space for designing high-performance photovoltaic metal halide perovskite devices.

Asymmetric acceptor DT-C8Cl with functional haloalkyl chains was designed and synthesized, where noncovalent interactions induced by haloalkyl chains could effectively optimize the morphology and suppress unfavorable morphology evolutions, leading to simultaneously enhanced efficiency and morphology stability of organic solar cells.

Abstract

The simultaneous improvement of efficiency and stability of organic solar cells (OSCs) for commercialization remains a challenging task. Herein, we designed asymmetric acceptors DT-C8Cl and DT-C8BTz with functional haloalkyl chains, in which the halogen atoms could induce noncovalent interactions with heteroatoms like O, S, and Se, etc., thus leading to appropriately manipulated film morphology. Consequently, binary devices based on D18: DT-C8Cl achieved a champion power conversion efficiency (PCE) of 19.40 %. The higher PCE of D18: DT-C8Cl could be attributed to the enhanced π–π stacking, improved charge transport, and reduced recombination losses. In addition, the noncovalent interactions induced by haloalkyl chains could effectively suppress unfavorable morphology evolutions and thereby reduce trap density of states, leading to improved thermal and storage stability. Overall, our findings reveal that the rational design of asymmetric acceptors with functional haloalkyl chains is a novel and powerful strategy for simultaneously enhancing the efficiency and stability of OSCs.

A fully non-fused acceptor, GS70, is synthesized by incorporating 1-(2-butyloctyl)-1H-pyrrole as a π-bridge, aiming to reduce material costs and enhance stability. The obtained active layers exhibit favorable morphology and effectively suppress charge recombination. Encouragingly, this design leads to the realization of high-efficiency and stable single-junction and parallel tandem OSCs.

Abstract

Organic solar cells (OSCs) are still suffering from the low light utilization and unstable under ultraviolet irradiation. To tackle these challenges, we design and synthesize a non-fused acceptor based on 1-(2-butyloctyl)-1H-pyrrole as π-bridge unit, denoted as GS70, which serves as active layer in the front-cell for constructing tandem OSCs with a parallel configuration. Benefiting from the well-complementary absorption spectra with the rear-cell, GS70-based parallel tandem OSCs exhibit an improved photoelectron response over the range between 600–700 nm, yielding a high short-circuit current density of 28.4 mA cm⁻². The improvement in light utilization translates to a power conversion efficiency of 19.4 %, the highest value among all parallel tandem OSCs. Notably, owing to the intrinsic stability of GS70, the manufactured parallel tandem OSCs retain 84.9 % of their initial PCE after continuous illumination for 1000 hours. Overall, this work offers novel insight into the molecular design of low-cost and stability non-fused acceptors, emphasizing the importance of adopting a parallel tandem configuration for achieving efficient light harvesting and improved photostability in OSCs.

Nature Photonics, Published online: 29 January 2024; doi:10.1038/s41566-024-01381-7

A new p-type 1D perovskite (5-Azaspiro[4.4]nonan-5-ium lead triiodide, ASNPbI₃) with excellent hydrophobic property and thermal stability is obtained, which can be in-situ grown on a n-type CsPbI₃ perovskite as a capping layer. The p-n heterojunction not only accelerates carrier separation but also reduces defect density. Consequently, the CsPbI₃ C-PSCs without hole transporter achieve a record efficiency of 18.34%.

Abstract

CsPbI₃ perovskite is a promising light absorber in perovskite solar cells (PSCs) due to its suitable bandgap (E _g) and high chemical stability, but the perovskite phase is metastable in ambient atmosphere and prone to defect formation. To enhance phase stability and reduce defects, forming a low dimensional (LD) perovskite on CsPbI₃ has proved effective. However, the energy levels for most of low-conductivity LD perovskites are not very compatible with those of CsPbI₃, which will impair charge separation and device performance. Herein, a new 1D perovskite (5-Azaspiro[4.4]nonan-5-ium lead triiodide, ASNPbI₃) with compatible energy levels and a large E _g is reported as a capping layer. The p-type ASNPbI₃ forms a p-n heterojunction with n-CsPbI₃ with a staggered band alignment, considerably enhancing the carrier separation. Besides, by pre-forming a ASNPbI₃ at an intermediate stage, defects are suppressed in perovskite film. Consequently, the CsPbI₃ PSCs based on carbon electrode without hole transporter (C-PSCs) achieves a PCE of 18.34%, which is among the highest-reported values for inorganic C-PSCs. Furthermore, the hydrophobic ASNPbI₃ capping layer has a high thermal stability that greatly enhances perovskite phase stability. Hence, the CsPbI₃ C-PSCs maintains 68% of its initial PCE after 400 h aging at 85°C in a N₂ glovebox.

A new asymmetric acceptor L8-CBIC-Cl with a high LUMO energy level and strong luminous properties is developed, which demonstrates great promise as a guest acceptor in realizing low non-radiation energy loss and high-performance ternary organic solar cells.

Abstract

The ternary strategy has proven to be an effective method for improving the efficiency of organic solar cells (OSCs). However, designing and selecting the third component still pose challenges. In this study, this issue is addressed by focusing on the PBDB-T:Y18-F binary system and introducing a new, strong luminescent, asymmetric small-molecule acceptor (SMA) called L8-CBIC-Cl, which shares a similar skeleton with Y18-F. The similarity in molecular framework facilitates good compatibility between the two acceptors, resulting in the formation of an alloy-like acceptor phase. Furthermore, the norbornenyl-modified end group in L8-CBIC-Cl contributes to its strong luminescent properties, which in turn leads to a low non-radiative energy loss and a high open-circuit voltage. Consequently, the PBDB-T:L8-CBIC-Cl:Y18-F based ternary devices realize a high power conversion efficiency (PCE) up to 17.01%, which is higher than PBDB-T:Y18-F device (14.49%). Importantly, L8-CBIC-Cl exhibits a good universality as a guest acceptor in other three binary systems (D18:Y6, D18:BTP-eC9-4F, and D18:L8-BO). The D18:L8-BO:L8-CBIC-Cl device shows an impressive efficiency of 19%. The work demonstrates that employing SMA with a high PLQY and better miscibility with host acceptor as the third component has a great potential for developing high-efficiency ternary OSCs.

Indium ion (In³⁺) is introduced into the perovskite precursor solution to balance the interaction rate of SnI₂ and PbI₂ with organic salt. In³⁺ has a lower reduction potential compared to Sn²⁺, so it generates an extra energy barrier for Sn²⁺ oxidation. The optimal devices achieve a PCE of 23.34%, one of the highest PCEs for solar cells made by PCBM.

Abstract

Low-bandgap mixed tin (Sn)-lead (Pb) perovskite solar cells promise efficiency beyond the pure-Pb ones. However, the difference in the interaction rate of SnI₂ and PbI₂ with organic salts causes spatial distribution heterogeneity of Sn²⁺ and Pb²⁺ in mixed Sn─Pb perovskite layers. This causes a Sn-rich surface, which can trigger more severe Sn²⁺ oxidation and nonradiative recombination. A strategy, of introducing indium ion (In³⁺) into the perovskite precursor solution to compete with Sn²⁺ when reacting with organic salts is developed. Therefore, the nucleation and crystallization of perovskite films are well-controlled, leading to improved film quality with a more balanced Sn/Pb ratio on the film surface. Additionally, In³⁺ has a lower reduction potential compared to Sn²⁺ which can generate an extra energy barrier for Sn²⁺ oxidation. The improved film quality and reduced surface oxidation result in accelerated electron transfer and reduced carrier recombination rate. The modified devices achieve a power conversion efficiency (PCE) of 23.34%, representing one of the highest PCEs in mixed Sn─Pb solar cells made with PCBM.

Depending on their distinctive material properties and diverse structures, carbon materials can be applied as conductive electrodes in perovskite solar cells (PSCs). Benefiting from the low cost and scalable preparation process, carbon material electrodes can remarkably reduce the raw materials and manufacturing costs of PSCs, which holds significant commercial implications.

Over the past decade, perovskite solar cells (PSCs) have achieved significant achievements. But the golden triangle problem of commercial development, which encompasses high efficiency, high stability, and low cost, remains unresolved. Carbon materials exhibit a diverse range of morphological structures and possess numerous advantages. They are extensively used in PSCs to overcome the challenges encountered during PSCs commercialization. The PSCs utilizing graphene as the top electrodes not only deliver an impressive efficiency of 22.8%, but also show exceptional long-term stability. The PSCs using carbon nanotubes as transparent conductive electrodes obtain an efficiency of 19%, exhibiting significant potential for scalable applications. Herein, the advantages of carbon materials as conductive electrodes are overviewed. The compatibility of carbon materials as conductive electrodes in PSCs, along with the associated challenges, regulatory strategies, and device performance are systematically discussed in terms of their intrinsic characteristics. The application of carbon materials derived from petroleum by-products and biomass in the top electrodes of PSCs are summarized in detail. Finally, the underlying reasons why PSCs using carbon electrode show a comparatively lower efficiency when compared to conventional devices is analyzed in-depth. The potential research directions are proposed to promote the development of carbon conductive electrodes in PSCs.

The large energy difference at SnO₂/CsPbBr₃ interface often leads to insufficient charge extraction. Herein, a thin layer of CdS/ZnS is introduced to solve this problem. Aside from the reduced energy loss, the defects at the buried interface are greatly reduced .The performances of CsPbBr₃ PSCs are increased from 8.16% (SnO₂) to 9.48% (ZnS-SnO₂) and 10.61% (CdS-SnO₂).

Although SnO₂ has been widely used as the electron transport material (ETM) of the perovskite solar cells (PSCs), the energy level mismatch at the SnO₂/CsPbBr₃ buried interface is as high as 1 eV, which is disastrous for the CsPbBr₃-based PSCs. Herein, a buffer layer of metal sulfide (CdS, ZnS) is introduced to solve this problem. The power conversion efficiency (PCE) of CsPbBr₃ PSCs has been increased from 8.16% to 9.48% for ZnS-treated SnO₂ (ZnS-SnO₂), and a champion efficiency of 10.61% has been achieved in CdS-treated SnO₂ (CdS-SnO₂) devices. Aside from the reduced energy loss, the mobility of the SnO₂ ETM has been greatly enhanced after the metal sulfide treatment. The CdS-SnO₂ devices also enjoy the benefits of reduced defect density and speeded carrier extraction, contributing to an almost 30% performance enhancement. This 10.61% PCE is among the highly efficient CsPbBr₃-based PSCs reported to date. Finally, CdS-SnO₂ devices survive a harsh damp heat test (120 °C with a relative humidity of 50%) for a month with less than 15% efficiency loss, demonstrating the superior stability of our CsPbBr₃ PSCs.

A relationship between the molecular structure and the vertical phase separation (VPS) morphology of PPHJ OSCs by using molecular surface electrostatic potential (ESP) as a bridge is first established. A ternary PPHJ device with an appropriate ∆ESP is elaborately constructed to achieve better VPS morphology and lower ΔE₃, resulting in impressive efficiency of 19.09%.

Abstract

Although a suitable vertical phase separation (VPS) morphology is essential for improving charge transport efficiency, reducing charge recombination, and ultimately boosting the efficiency of organic solar cells (OSCs), there is a lack of theoretical guidance on how to achieve the ideal morphology. Herein, a relationship between the molecular structure and the VPS morphology of pseudo-planar heterojunction (PPHJ) OSCs is established by using molecular surface electrostatic potential (ESP) as a bridge. The morphological evolution mechanism is revealed by studying four binary systems with vary electrostatic potential difference (∆ESP) between donors (Ds) and acceptors (As). The findings manifest that as ∆ESP increases, the active layer is more likely to form a well-mixed phase, while a smaller ∆ESP favors VPS morphology. Interestingly, it is also observed that a larger ∆ESP leads to enhanced miscibility between Ds and As, resulting in higher non-radiative energy losses (ΔE₃). Based on these discoveries, a ternary PPHJ device is meticulously designed with an appropriate ∆ESP to obtain better VPS morphology and lower ΔE₃, and an impressive efficiency of 19.09% is achieved. This work demonstrates that by optimizing the ΔESP, not only the formation of VPS morphology can be controlled, but also energy losses can be reduced, paving the way to further boost OSC performance.

The application of self-assembled monolayer (SAMs) in perovskite solar cells has made the performance of p–i–n structure devices develop rapidly, while the relationship of function group, anchor groups, and spacers often is neglected. It is found that anchoring groups and spacers can affect the coordination between SAMs and perovskite. This work demonstrates different components of perovskites are selective to SAMs.

Abstract

Self-assembled monolayers (SAMs) have displayed great potential for improving efficiency and stability in p–i–n perovskite solar cells (PSCs). The anchoring of SAMs at the conductiv metal oxide substrates and their interaction with perovskite materials must be rationally tailored to ensure efficient charge carrier extraction and improved quality of the perovskite films. Herein, SAMs molecules with different anchoring groups and spacers to control the interaction with perovskite in the p–i–n mixed Sn–Pb PSCs are selected. It is found that the monolayer with the carboxylate group exhibits appropriate interaction and has a more favorable orientation and arrangement than that of the phosphate group. This results in reduced nonradiative recombination and enhanced crystallinity. In addition, the short chain length leads to an improved energy level alignment of SAMs with perovskite, improving hole extraction. As a result, the narrow bandgap (≈1.25 eV) Sn–Pb PSCs show efficiencies of up to 23.1% with an open-circuit voltage of up to 0.89 V. Unencapsulated devices retain 93% of their initial efficiency after storage in N₂ atmosphere for over 2500 h. Overall, this work highlights the underexplored potential of SAMs for perovskite photovoltaics and provides essential findings on the influence of their structural modification.

Nature Photonics, Published online: 26 January 2024; doi:10.1038/s41566-024-01382-6

Nature Energy, Published online: 26 January 2024; doi:10.1038/s41560-024-01450-9

Nature Energy, Published online: 26 January 2024; doi:10.1038/s41560-024-01451-8

Crystallization control of perovskite thin films is the key in commerciallization of perovskite solar cells. However, the fast crystallization of the thin film including nucleation, growth and Oswald ripening, is still a mystery though some efforts made. According to the theories of nucleation and Oswald ripening, we modified the perovskite surface energy and improved the grain solubility, and quantified the nucleation and ripening rate in experiments.

Abstract

The power conversion efficiencies (PCEs) of perovskite solar cells have recently developed rapidly compared to crystalline silicon solar cells. To have an effective way to control the crystallization of perovskite thin films is the key for achieving good device performance. However, a paradox in perovskite crystallization is from the mismatch between nucleation and Oswald ripening. Usually, the large numbers of nucleation sites tend to weak Oswald ripening. Here, we proposed a new mechanism to promote the formation of nucleation sites by reducing surface energy from 44.9 mN/m to 36.1 mN/m, to spontaneously accelerate the later Oswald ripening process by improving the grain solubility through the elastic modulus regulation. The ripening rate is increased from 2.37 Åm ⋅ s⁻¹ to 4.61 Åm ⋅ s⁻¹ during annealing. Finally, the solar cells derived from the optimized films showed significantly improved PCE from 23.14 % to 25.32 %. The long-term stability tests show excellent thermal stability (the optimized device without encapsulation maintaining 82 % of its initial PCE after 800 h aging at 85 °C) and an improved light stability under illumination. This work provides a new method, the elastic modulus regulation, to enhance the ripening process.

Publication date: June 2024

Source: Journal of Energy Chemistry, Volume 93

Author(s): Qiaoqiao Zhao, Feng He

Starlike BD molecules possess an orderly stacking type by twisting acceptor unit, thus having a wide π system and high hole mobility. The BD CsPbI₃ perovskite solar cell (PSC) exhibits the champion efficiency of 19.19%, the highest performance for all-inorganic PSCs using dopant-free hole transport material. Meanwhile, a dense BD layer can inhibit ion migration, thus improving the device stability.

Abstract

All-inorganic n-i-p perovskite solar cells (PSCs) using doped Spiro-OMeTAD as hole transport material (HTM) suffer from photothermal stability due to ionic diffusion and radical-induced degradation by the dopants. In this article, dopant-free starlike molecule (N2, N2-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-N5,N5-bis(4-methoxyphenyl)pyridine-2,5-diamine (BD)) is synthesized to engineer the stacking properties and delivered higher hole mobility than doped Spiro-OMeTAD (3.2 × 10⁻⁴ versus 1.76 × 10⁻⁴ cm² V⁻¹ s⁻¹) as dopant-free HTM. Starlike BD HTM has a twisted acceptor unit and strong dipole, forming crystalline and ordered packing film to ensure intramolecular charge transfer and improve mobility. The BD CsPbI₃ PSCs deliver the maximum efficiency of 19.19%, which is the highest performance for all-inorganic PSCs based on dopant-free HTMs. Meanwhile, the ordered molecules-packing blocks the migration channel of I⁻ ions to metal electrodes and improves the device stability. BD-based devices maintain more than 93% and 80% of the initial efficiency after 85 °C storage for 35 days and maximum power point (MPP) tracking at 85 °C for 1000 h, respectively.

A Cu₂(Thiourea)Br₂ interfacial layer is introduced on the poly(triaryl amine) to improve the coverage of overlying perovskite precursors. Cu₂(Thiourea)Br₂, partially dissolved in the perovskite absorber, also enhances the device's band alignment. The associated inverted devices based on 1.63 eV perovskite can achieve over 21% efficiency on both 0.1 and 1.0 cm² cell sizes with improved reproducibility.

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) is one of the most efficient hole transport materials for p–i–n structured perovskite solar cells (PSCs). However, the hydrophobicity of PTAA causes wettability problems and is thereby associated with low yield and poor reproducibility. Herein, a new strategy for improving the perovskite precursor wettability on PTAA is developed. A Cu₂(Thiourea)Br₂ complex interfacial layer is introduced on the PTAA, improving the coverage of perovskite precursors and thereby the perovskite film. Partially dissolved Cu₂(Thiourea)Br₂ in the perovskite absorber further enhances band alignment and carrier extraction between layers. With the addition of Cu₂(Thiourea)Br₂ layer on nondoped PTAA, PSCs in p–i–n structure with a bandgap of 1.63 eV have achieved over 21% efficiency both on 0.1 and 1.0 cm² sized devices with a significantly improved yield and reproducibility. Unencapsulated devices retain 100% of their initial efficiency after 2000 h at 65 °C.

A facile passivator-assisted close space annealing strategy is proposed to simultaneously enlarge the grain size and passivation the defects through in situ sublimation of the passivators, leading to high-performance wide-bandgap perovskite solar cells and all-perovskite tandem solar cells.

Wide-bandgap perovskite solar cells (PSCs) play crucial roles in determining the overall efficiencies of all-perovskite tandem solar cells (TSCs). Tailoring the grain growth process is a key route to improve the film quality and device performance. Herein, a facile passivator-assisted close space annealing (PA-CSA) strategy to simultaneously enlarge the crystal size and passivate the defects is demonstrated. Filter paper is used as the solvent permeable membrane to slow down the fast crystallization and enlarge the grain size. At the same time, a precisely selected volatile material (fluorizated-phenethylammonium chloride) embedded in the filter paper is employed as the passivator to eliminate defects in wide-E _g perovskite film during annealing. The PA-CSA-processed wide-E _g PSCs obtain the champion efficiencies of 21.28% (1.68 eV) and 20.24% (1.73 eV), enabling high-performance all-perovskite TSCs with efficiencies reaching 27% in both four-terminal and monolithic two-terminal tandem configurations, respectively. This PA-CSA strategy provides an in situ passivating process for high-performance PSCs and TSCs upon further industrial applications.

Compared with the conventional hole-transport layer used in inverted PSCs, hole-selective self-assembled monolayers provide multiple advantages, including conformal and uniform coating, minimized thickness, negligible optical and resistance loss, and the versatility in the interface modification.

Hole-transport layer (HTL) is of paramount importance to construct high-performance inverted perovskite solar cells (PSCs) because it not only determines the hole extraction and transport but also influences the quality of perovskite layer. Recently, self-assembled monolayers are adopted as very effective hole-selective layer to construct high-performance inverted PSCs. Compared with conventional HTL, hole-selective self-assembled monolayers (HSSAMs) offer the benefits of minimal material consumption and parasitic absorption, simple and scalable processing, and the versatility in the interface modification. Through molecule design and coating process optimization, the high-quality HSSAMs are obtained, which enable the HSSAM-based inverted PSCs to achieve greatly promoted photovoltaic performance. Herein, the progress of HSSAMs used in inverted PSCs is summarized. First, the structure characteristics of HSSAM molecules are described. Then, the effect of the structure of HSSAM molecules on their function in boosting the device performance and stability is discussed. Furthermore, the deposition strategies to form high-quality HSSAMs for inverted PSCs are analyzed. Finally, the advantages and challenges associated with application of HSSAMs in inverted PSCs are discussed, and the perspectives of the future research trends on HSSAMs for further promoting the performance of inverted PSCs are suggested.

A hydrolysis reaction regulation strategy is proposed to achieve multifunctional modification of the buried interface of perovskite films by introducing N-chlorosuccinimide (NCS) into SnO₂ solution. The device based on CsFAMA triple cation perovskite achieved a champion power conversion efficiency (PCE) of 24.74% with an ultra-high fill factor, and showed an excellent long-term stability performance.

Abstract

Mixed-cation perovskite solar cells (PSCs) have attracted much attention because of the advantages of suitable bandgap and stability. It is still a challenge to rationally design and modify the perovskite/tin oxide (SnO₂) heterogeneous interface for achieving highly efficient and stable PSCs. Herein, a strategy of one-stone-for-three-birds is proposed to achieve multi-functional interface regulation via introducing N-Chlorosuccinimide (NCS) into the solution of SnO₂: i) C═O functional group in NCS can induces strong binding affinity to uncoordinated defects (oxygen vacancies, free lead ions, etc) at the buried interface and passivate them; ii) incomplete in situ hydrolysis reactions can occur spontaneously and adjust the pH value of the SnO₂ solution to achieve a more matchable energy level; iii) effectively releasing the residual stress of the underlying perovskite. As a result, a champion power conversion efficiency (PCE) of 24.74% is achieved with a device structure of ITO/SnO₂/Perovskite/Spiro-OMeTAD/Ag, which is one of the highest values for cesium-formamidinium-methylammonium (CsFAMA) triple cation PSCs. Furthermore, the device without encapsulation can sustain 94.6% of its initial PCE after the storage at room temperature and relative humidity (RH) of 20% for 40 days. The research provides a versatile way to manipulate buried interface for achieving efficient and stable PSCs.

An anion stabilization strategy is developed to simultaneously realize the excellent stability from precursor solution and films to final devices in the whole air preparation process. The influence of different anion species on the efficiency and stability of two-step deposited PSCs is comprehensively investigated and evaluated. Finally, TFSI-treated PSCs deliver an impressive efficiency of 24.16% with superior environmental and mechanical stability.

Abstract

Despite the outperforming power conversion efficiency of low-temperature and solution-processed perovskite solar cells (PSCs) realized over the past decades, the undesirable stability from precursor inks to resultant devices and harsh preparation requirements still restrain their industrial production and practical deployment. Herein, an anion stabilization strategy is developed to achieve the comprehensive durability of perovskite photovoltaics throughout the whole two-step air-processed procedure. The effect of interionic bonding strengths on the ink properties, film crystallization, and photovoltaic performances is in-depth explored and revealed. The pseudohalide bis(trifluoromethanesulfonyl)imide ions (TFSI⁻) not only improve the dispersion and stabilities of lead polyhalides and organic salt inks via strong electron-withdrawing/donating chemical sites, but also realize high composition uniformity and preferential crystal growth of subsequent deposited perovskite layers by tuning the precursor reactivity and surface absorption. Ultimately, the optimizing PSCs deliver a superior efficiency of 24.16%, accompanied by notably improved long-term stability toward extreme environmental and mechanical stimuli with lead leakage suppression. This work opens up a promising avenue toward reproducible air preparation of highly efficient, stable, and environmentally friendly perovskite optoelectronic devices via precise modulation of precursor properties.

Nature Energy, Published online: 23 January 2024; doi:10.1038/s41560-023-01438-x