Chen Weijie

Seed-assisted growth is an effective method to improve the crystallization quality without increasing the temperature. The seeds provide preferential nucleation sites so that the crystallization does not need to overcome the critical free energy. Via this strategy, tin oxide layer with enhanced crystal quality, reduced defect, larger conductivity, and mobility can be achieved at low temperature.

Tin oxide has been the mainstream as the electron transport layer for highly efficient perovskite solar cells due to advantages such as high mobility, high transmittance, and strong UV stability. Realizing high-quality SnO₂ layer at low temperature can widen the range of potential applications on both rigid and flexible substrates. Herein, a seed-assisted growth strategy is developed for the preparation of SnO₂ layer at low temperature (100 °C) and the seeds in precursor solution provide preferential nucleation sites. The SnO₂ layer via seed-assisted growth exhibits higher conductivity and mobility which are more than twice those of control samples because of enhanced crystallinity. The resulting solar cells show high V _oc of 1.189 V, contributing to a high power conversion efficiency of 25.26%. To current knowledge, this is the highest efficiency for perovskite solar cells with SnO₂ layer formed at low temperature (≤100 °C). Contributed by the high-quality SnO₂ layer prepared at low temperature, a high power conversion efficiency over 22% for flexible perovskite solar cells is also achieved.

An electron beam process to simultaneously improve the efficiency and stability of organic solar cells is developed. Electrons generated from Ar plasma, are accelerated, and irradiated onto the surface of ZnO introduced as an electron transport layer. Expected commercialization due to dramatic improvement in environmental, thermal, and operational stability.

The commercialization of organic photovoltaics (OPVs) requires a high level of stability and a high-power conversion efficiency (PCE). To satisfy these requirements, inverted OPVs with electron transport layers of ZnO obtained by electron beam annealing (EBA) are fabricated, and their properties are compared with those of a reference device with a thermal-treated ZnO layer. Electrons are extracted from Ar plasma and accelerated by supplying a negative DC voltage; the ZnO layer is annealed using the energy from the accelerated electrons. The PCE of the OPV with a ZnO layer obtained by the optimal EBA process is 15.6%, which is 11.4% higher than that of the reference device. In addition, the OPV device retains 90.1% of its initial PCE after it is stored at room temperature for 30 days and 70.1% of the initial PCE after 280 h at 90 °C. Further, the operational stability is measured for 500 min at the maximum power point under 1 sun illumination in ambient air. The OPV with the ZnO layer treated under optimal EBA conditions retains 85.0% of the initial PCE and shows outstanding environmental and thermal stability.

A commonly used fluorescent dye, rhodamine 110 chloride (RC110), is designed to synergistically achieve colloidal coordination regulation and defect passivation. The formation of the halogen-dopants compound reduces the colloid density and facilitates the crystallization process. The crystalline quality of the perovskite film is significantly improved. The champion perovskite solar cell achieves a 21.02% efficiency.

Mixed-cation lead mixed-halide perovskite have attracted extensive attention due to their application potential in tandem devices and favorable stability. However, the crystallization of mixed-component perovskite usually suffers from more complicated phase-transition processes, making it difficult to prepare high-quality perovskite films. Herein, it is demonstrated that rhodamine 110 chloride (RC110) additive, a commonly used fluorescent dye, plays significant roles in improving the performance of perovskite solar cells (PSCs). It is shown that the defects can be remarkably reduced by interactions between the defects and the functional groups, the interaction between the RC110 and halogen ions in precursor solution can exert significant effects on the coordination level of lead–halogen octahedral frameworks, and thereby augments the colloidal size in the precursor solution. Leveraging these benefits, the liquid–solid coregulation engineering endows high-quality perovskite films with enhanced crystallinity, lower defects density, reduced nonradiative recombination, and prolonged carrier lifetime. Consequently, the RC110-treated planar devices deliver a champion efficiency of 21.02% with negligible hysteresis and exhibit excellent stability. Briefly, this defect passivation strategy based on colloidal coordination engineering provides a novel and feasible route to promote the potential commercialization of PSCs.

The effect of ionization energy (IE) offsets on charge generation and generation recombination in planar heterojunction organic solar cells is systematically investigated. An IE offset of about 0.5 eV is required for efficient hole transfer and subsequent free charge generation. Furthermore, in systems with high IE offset, bimolecular charge recombination and consequently triplet generation are significantly reduced.

The ionization energy (IE) offset of a donor–acceptor pair provides the driving force for hole transfer and subsequent free charge carrier generation in low-bandgap nonfullerene organic solar cells (OSCs). However, the interfacial energetic landscape in bulk heterojunction OSCs is determined by the materials’ electronic structure and intermolecular interactions at the donor/acceptor interface, causing local energy-level shifts and disorder. Herein, the impact of the IE offset on the charge transfer efficiency and charge carrier dynamics is systematically evaluated by characterizing PM6/ITIC, PM6/IT-2Cl, and PM6/IT-4Cl planar heterojunction (PHJ) solar cells. Ultrafast spectroscopy and time-resolved charge carrier density measurements reveal that an IE offset of about ≈0.5 eV leads to efficient hole transfer and subsequent free charge generation. Furthermore, bimolecular charge recombination and consequently triplet generation are significantly reduced in systems with high IE offset. This work underlines the importance of sizeable donor–acceptor IE offsets in PHJ nonfullerene OSCs as critical for high-efficiency donor/acceptor material and device design.

Two chlorine regioisomeric units are developed and incorporated into star polymer PM6 to achieve one of the most efficient polymer donors for organic solar cells. It is demonstrated that Cl-regioisomerization not only affects molecular coplanarity, crystallinity, and aggregation behavior, but also modulates electrostatic potential, donor–acceptor interaction, and phase-separation morphology, which are of great importance for device performance.

Abstract

Terpolymerization and regioisomerization strategies are combined to develop novel polymer donors to overcome the difficulty of improving organic solar cells (OSCs) performance. Two novel isomeric units, bis(2-hexyldecyl)-2,5-bis(4-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTO) and bis(2-hexyldecyl) 2,5-bis(3-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTI), are obtained and incorporated into the PM6 backbone via random copolymerization to form a series of terpolymers. Interestingly, it is found that different chlorine (Cl) substituent positions can significantly change the molecular planarity and electrostatic potential (ESP) owing to the steric hindrance effect of the heavy Cl atom, which leads to different molecular aggregation behaviors and miscibility between the donor and acceptor. The TTO unit features a higher number of multiple S···O non-covalent interactions, more positive ESP, and fewer isomer structures than TTI. As a result, the terpolymer PM6-TTO-10 exhibits a much better molecular coplanarity, stronger crystallinity, more obvious aggregation behavior, and proper phase separation in the blend film, which are conducive to more efficient exciton dissociation and charge transfer. Consequently, the PM6-TTO-10:BTP-eC9-based OSCs achieve a champion power conversion efficiency of 18.37% with an outstanding fill factor of 79.97%, which are among the highest values reported for terpolymer-based OSCs. This work demonstrates that terpolymerization combined with Cl regioisomerization is an efficient approach for achieving high-performance polymer donors.

Publication date: July 2023

Source: Journal of Energy Chemistry, Volume 82

Author(s): Daizhe Wang, Cong Kang, Tengling Ye, Dongqing He, Shan Jin, Xiaoru Zhang, Xiaochen Sun, Yong Zhang

By replacing 2D and 1D perovskite in the surface heterojunction of perovskite solar cells, a durable polymer/perovskite heterostructure with uniformly anchored quaternized polystyrene was demonstrated to inhibit the interfacial diffusion. The strong anchoring of quaternary ammonium groups at the interface and the ultra-high molecular weight made polymer hardly volatilize and migrate.

Abstract

Surface heterojunction has been regarded as an effective method to improve the device efficiency of perovskite solar cells. Nevertheless, the durability of different heterojunction under thermal stress is rarely investigated and compared. In this work, benzylammonium chloride and benzyltrimethylammonium chloride are utilized to construct 3D/2D and 3D/1D heterojunctions, respectively. A quaternized polystyrene is synthesized to construct a three-dimensional perovskite/amorphous ionic polymer (3D/AIP) heterojunction. Due to the migration and volatility of organic cations, severe interfacial diffusion is found among 3D/2D and 3D/1D heterojunctions, in which the quaternary ammonium cations in the 1D structure are less volatile and mobile than the primary ammonium cations in the 2D structure. 3D/AIP heterojunction remains intact under thermal stress due to the strong ionic bond anchoring at the interface and the ultra-high molecular weight of AIP. Furthermore, the dipole layer formed by AIP can further reduce the voltage loss caused by nonradiative recombination at the interface by 0.088 V. Therefore, the devices based on the 3D/AIP heterojunction achieve a champion power conversion efficiency of 24.27% and maintain 90% of its initial efficiency after either thermal aging for 400 h or wet aging for 3000 h, showing a great promise for polymer/perovskite heterojunction towards real applications.

A non-fullerene acceptor of CH23 is constructed simply by peripheral halogen swapping on a high-performance molecular platform of CH14. Due to enhanced dielectric features and intermolecular interactions, CH23-based binary organic solar cells achieve an excellent efficiency of 18.77%, exhibiting the best value for the newly explored CH-series non-fullerene acceptors.

Abstract

Peripheral halogen regulations can endow non-fullerene acceptors (NFAs) with enhanced features as organic semi-conductors and further boost efficient organic solar cells (OSCs). Herein, based on a remarkable molecular platform of CH14 with more than six halogenation positions, a preferred NFA of CH23 is constructed by synergetic halogen swapping on both central and end units, rendering the overall enlarged molecular dipole moment, packing density and thus relative dielectric constant. Consequently, the CH23-based binary OSC reaches an excellent efficiency of 18.77% due to its improved charge transfer/transport dynamics, much better than that of 17.81% for the control OSC of CH14. This work demonstrates the great potential for further achieving state-of-the-art OSCs by delicately regulating the halogen formula on these newly explored CH-series NFAs.

Tetrabutylammonium bromide functionalized Ti₃C₂T_x (TBAB-Ti₃C₂T_x) is developed as cathode buffer layer (CBL) in perovskite solar cells (PVSCs). The TBAB-Ti₃C₂T_x CBL enables optimization of energy level alignment and enhancement of charge extraction and inhibition of the iodine ions migration from perovskite layer to Ag cathode. The TBAB-Ti₃C₂T_x based device exhibits a dramatically improved efficiency of 21.65% with significantly improved operational stability.

Abstract

2D Ti₃C₂T_x MXene, possessing facile preparation, high electrical conductivity, flexibility, and solution processability, shows good application potential for enhancing device performance of perovskite solar cells (PVSCs). In this study, tetrabutylammonium bromide functionalized Ti₃C₂T_x (TBAB-Ti₃C₂T_x) is developed as cathode buffer layer (CBL) to regulate the PCBM/Ag cathode interfacial property for the first time. By virtue of the charge transfer from TBAB to Ti₃C₂T_x demonstrated by electron paramagnetic resonance and density functional theory, the TBAB-Ti₃C₂T_x CBL with high electrical conductivity exhibits significantly reduced work function of 3.9 eV, which enables optimization of energy level alignment and enhancement of charge extraction. Moreover, the TBAB-Ti₃C₂T_x CBL can effectively inhibit the migration of iodine ions from perovskite layer to Ag cathode, which synergistically suppresses defect states and reduce charge recombination. Consequently, utilizing MAPbI₃ perovskite without post-treatment, the TBAB-Ti₃C₂T_x based device exhibits a dramatically improved power conversion efficiency of 21.65% with significantly improved operational stability, which is one of the best efficiencies reported for the devices based on MAPbI₃/PCBM with different CBLs. These results indicate that TBAB-Ti₃C₂T_x shall be a promising CBL for high-performance inverted PVSCs and inspire the further applications of quaternary ammonium functionalized MXenes in PVSCs.

Two new small molecule donor isomers, with α and β-chlorinated thiophene as side chain, are systematically designed, synthesized, and incorporated as a third component in PM6:L8-BO binary blends. Benefiting from the extension of absorption, more favored morphology, enhanced crystallinity and reduced recombination loss, the resultant ternary devices achieve impressive champion power conversion efficiency of 18.96%.

Abstract

Ternary organic solar cells (OSCs) represent an efficient and facile strategy to further boost the device performance. However, the selection criteria and rational design of the third guest small molecule (SM) material still remain less understood. In this study, two new SM donor isomers, with α-chlorinated thiophene (αBTCl) and β-chlorinated thiophene (βBTCl) as side chains, are systematically designed, synthesized and incorporated as a third component in PM6:L8-BO binary blends. It is noticed that introducing the SM donors guest has extended the absorption of photo-active layer, induced desired component distribution vertically with enhanced crystallinity and reduced recombination process, leading to increased short-circuit current (J _SC) and improved fill factor. Moreover, due to the synergetic suppressed nonradiative loss and preferable morphology, the ternary OSCs feature improves open-circuit voltage (V _OC). Consequently, an impressive champion power conversion efficiency of 18.96% and 18.55% is achieved by αBTCl-based and βBTCl-based ternary OSCs, respectively. Furthermore, a record efficiency of 17.46% is obtained with a 330 nm thickness of αBTCl-based ternary OSCs. This study demonstrates that molecular isomerization can be a promising design approach for SM donors to construct high-performance ternary OSCs with simultaneous enhancement of all photovoltaic parameters.

A thermal annealing-free post-treatment method using a 2-thiopheneethylammonium chloride molecule is employed to form an n = 1 2D perovskite capping layer on wide-bandgap perovskites. Thus, opaque and semi-transparent 1.66 eV-bandgap methylamine-free perovskite solar cells realize efficiencies of 21.47% and 19.11%, respectively. Furthermore, four-terminal all-perovskite tandem cells deliver a remarkable efficiency of 26.64%.

Abstract

Wide-bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open-circuit voltage (V _OC) deficit and serious photo-induced halide segregation remain the main challenges that impede their applications. Herein, a post-treatment strategy without thermal annealing is presented to form a 2D top layer of 2-thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing-free post-treatment method can more effectively passivate the defects of WBG methylamine (MA)-free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo-induced perovskite phase segregation, as compared with the thermal annealing method that yields multi-2D phases. The resulting opaque and semi-transparent 1.66 eV-bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small V _OC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA-free WBG PSCs. Consequently, four-terminal all-perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi-junction tandem solar cells.

The researchers developed a novel in situ passivation of SnO₂ with optimized SnO₂/perovskite interfacial carrier extraction and transport for efficient and stable perovskite solar cells (PSCs). A champion power conversion efficiency (PCE) of 24.91 % and a champion fill factor (FF) up to 0.852 were obtained.

Abstract

Perovskite solar cells (PSCs) based on SnO₂ electron transport layers have attracted extensive research due to their compelling photovoltaic performance. Herein, we presented an in situ passivation of SnO₂ with low-cost hydroxyacid potassium synergist during deposition to optimize the interface carrier extraction and transport for high power conversion efficiency (PCE) and stabilities of PSCs. The orbital overlap of the carboxyl oxygen with the Sn atom alongwith the homogenous nano-particle deposition effectively suppresses the interfacial defects and releases the internal residual strains in the perovskite. Accordingly, a PCE of 24.91 % with a fill factor (FF) up to 0.852 is obtained for in situ passivated devices, which is one of the highest values for SnO₂-based PSCs. Moreover, the unencapsulated device maintained 80 % of its initial PCE at 80 °C over 600 h, 100 % PCE at ambient conditions for 1300 h, and 98 % after one week maximum power point tracking (MPPT) under continuous AM1.5G illumination.

In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved in perovskite frameworks is visualized by investigating the precursor species. The feasibility of modulating the quantum wells structure for the fabrication of low-dimensional perovskite photovoltaics is further verified.

Abstract

The multiple quantum wells (QWs) distribution in low-dimensional perovskite films hinders charge transport due to the fundamental difficulty of controlling crystal growth from precursor solutions, yielding poorly homogeneous low-dimensional perovskite solar cells (PSCs), especially in upscaling fabrication. Here, efficient low-dimensional PSCs are realized by modulating the colloidal assembly behavior in the precursor solution to induce intermediate structures. In combination with in situ liquid time-of-flight secondary ion mass spectrometry, the assembly behavior of organic cations involved lead iodide-dominated colloidal soft framework is visualized by investigating the precursor species differences under hydrogen bonding interactions. Subsequently, solid-state reactions emerge and the formamidine (FA)-based perovskite films exhibit significantly suppressed multiple QWs distribution. Encouragingly, the FA device (n=9, by meniscus-assisted coating) achieves a power conversion efficiency (PCE) of 20.28 % for a size of 0.04 cm² and a PCE of 15.35 % for a mini-module of 16.94 cm² with superior stability.

The resultant perovskite solar cells are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. This review aims to provide a thorough understanding of the origin of ion migration and the action of effective inhibition strategies that are essential for the development of “state-of-the-art” perovskite solar cells with high intrinsic stability to accelerate commercialization.

Abstract

In recent years, organic-inorganic halide perovskites are now emerging as the most attractive alternatives for next-generation photovoltaic devices, due to their excellent optoelectronic characteristics and low manufacturing cost. However, the resultant perovskite solar cells (PVSCs) are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. There is no doubt that the investigation of ion migration and the summarization of recent advances in inhibition strategies are necessary to develop “state-of-the-art” PVSCs with high intrinsic stability for accelerated commercialization. This review systematically elaborates on the generation and fundamental mechanisms of ion migration in PVSCs, the impact of ion migration on hysteresis, phase segregation, and operational stability, and the characterizations for ion migration in PVSCs. Then, many related works on the strategies for inhibiting ion migration toward highly efficient and stable PVSCs are summarized. Finally, the perspectives on the current obstacles and prospective strategies for inhibition of ion migration in PVSCs to boost operational stability and meet all of the requirements for commercialization success are summarized.

Nature Energy, Published online: 17 April 2023; doi:10.1038/s41560-023-01249-0

Publication date: July 2023

Source: Nano Energy, Volume 112

Author(s): Yuqin Zou, Johanna Eichhorn, Sebastian Rieger, Yiting Zheng, Shuai Yuan, Lukas Wolz, Lukas V. Spanier, Julian E. Heger, Shanshan Yin, Christopher R. Everett, Linjie Dai, Matthias Schwartzkopf, Cheng Mu, Stephan V. Roth, Ian D. Sharp, Chun-Chao Chen, Jochen Feldmann, Samuel D. Stranks, Peter Müller-Buschbaum

We developed a simple “two-step” in situ reaction approach to construct stable tungstate/perovskite (PVSK) heterointerfaces at grain boundary grooves (GBGs) in perovskite solar cells. The proposed passivation involved strong ionic bonds with explicitly tuned band energetics in the heterointerface. Accordingly, the uncoordinated Pb²⁺ could be effectively passivated via the tungstate ions, meanwhile the type-I PVSK/tungstate heterointerfaces could reduce recombination loss via repelling carriers from grain boundaries back to the intra-grain section. Thus, the resulting sample showed improved device performance both in the p-i-n and n-i-p structure, which demonstrated the universality and validity of our passivation strategy.

Abstract

Possessed with advantageous optoelectronic properties, perovskites have boosted the rapid development of solution-processed solar cells. The performance of perovskite solar cells (PSCs) is significantly weakened by the carrier loss at grain boundary grooves (GBGs); however, it receives limited attention and there lacks effective approach to solve this issue. Herein, for the first time, we constructed the tungstate/perovskite heterointerface via a “two step” in situ reaction approach that provides effective defect passivation and ensures efficient carrier dynamics at the GBGs. The exposed perovskite at grain boundaries is converted to wide-band-gap PbWO₄ via an in-situ reaction between Pb²⁺ and tungstate ions, which passivate defects due to the strong ionic bonding. Moreover, recombination loss is further suppressed via the heterointerface energetics modification based on an additional transformation from PbWO₄ to CaWO₄. PSCs based on this groove modification strategy showed good universality in both normal and inverted structure, with an improved efficiency of 23.25 % in the n-i-p device and 23.33 % in the p-i-n device. Stable power output of the modified device could maintain 91.7 % after around 1100 h, and the device efficiency could retain 92.5 % after aging in air for around 2110 h, and 93.1 % after aging at 85 °C in N₂ for 972 h.

Publication date: 15 June 2023

Source: Nano Energy, Volume 111

Author(s): Hae-Jun Seok, Jung-Min Park, Jaehoon Jeong, Shuai Lan, Doh-Kwon Lee, Han-Ki Kim

A buried interface engineering with an amphiphilic molecule hexadecyltrimethylammonium chloride treatment is employed to optimize the wettability of the hydrophobic hole transport layer poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] and passivate the perovskite defects simultaneously, achieving an improved power conversion efficiency from 20.65% to 22.04% for inverted perovskite solar cells, along with a good stability.

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), as an extensively used hole transport material in inverted perovskite solar cells (PSCs), has given reason for concern due to its hydrophobicity for a long time. Herein, buried interface engineering is applied for the scalable deposition of perovskite films by introducing an amphiphilic molecule hexadecyltrimethylammonium chloride on the PTAA surface, which improves the interfacial wettability of the perovskite precursor solution on the organic hole transport layer (HTL), facilitates the nucleation and growth of perovskites, and reduces the nonradiative recombination at the perovskite/HTL interface. As a result, all photovoltaic parameters of the inverted PSCs are improved significantly. The champion devices demonstrate power conversion efficiencies (PCEs) of 22.04% and 20.47% with aperture areas of 0.148 and 1.0 cm², respectively. Moreover, the encapsulated 1.0 cm² device exhibits excellent stability and maintains over 70% of its initial PCE after 1200 h under continuous 1 sun illumination at 65 °C in a nitrogen environment.

Constructing more efficient and functional polymer photovoltaic materials is urgently needed for the further development of polymer solar cells. In this review, the functions of random copolymerization strategy are first discussed, then the recent research progress of random copolymer materials is reviewed, and finally perspectives on the further advancement of random copolymers are put forward.

Along with the development of narrow-bandgap A–D–A and A–DA’D–A-type small-molecule acceptors (SMAs), polymer solar cells (PSCs) have witnessed a striking progress, with an impressing power conversion efficiency (PCE) approaching 20% recently. Aiming to realize the future commercial application of organic photovoltaic (OPV) technology, developing more efficient organic conjugated materials is urgently needed. Benefiting from the specific advantages in precisely adjusting the optoelectronic materials, random copolymerization strategy has drawn great attention during the past several years and has played a vital role in the development of PSCs. Herein, the functions of random copolymerization strategy in modulating the polymer properties are briefly discussed. Then the recent research progress of random copolymerization strategy of polymer photovoltaic materials in PSCs is reviewed. Finally, perspectives and a concise outlook on the further advancement of the random copolymerization strategy are put forward.

Publication date: 17 May 2023

Source: Joule, Volume 7, Issue 5

Author(s): Yang Liu, Hongpeng Zhou, Yongfeng Ni, Junxue Guo, Ruixue Lu, Can Li, Xin Guo

A straightforward method involves utilizing 2-amino-5-bromobenzamide (ABA) to fabricate efficient inorganic perovskite solar cells (IPSCs) by reconfiguring the surface properties of CsPbI_2.85Br_0.15 film. A record-breaking efficiency of 20.38% for p–i–n single-junction IPSCs is obtained. Furthermore, an inorganic perovskite/silicon tandem solar cell is successfully demonstrated, with an impressive efficiency of 25.31%.

Abstract

Inorganic perovskite solar cells (IPSCs) have garnered attention in tandem solar cells (TSCs) due to their suitable bandgap and impressive thermal stability. However, the efficiency of inverted IPSCs has been limited by the high trap density on the top surface of inorganic perovskite film. Herein, a method for fabricating efficient IPSCs by reconfiguring the surface properties of CsPbI_2.85Br_0.15 film with 2-amino-5-bromobenzamide (ABA) is developed. This modification not only exhibits the synergistic coordination of carbonyl (C=O) and amino (NH₂) groups with uncoordinated Pb²⁺, but also the Br fills halide vacancies and suppresses the formation of Pb⁰, effectively passivating the defective top surface. As a result, a champion efficiency of 20.38%, the highest efficiency reported for inverted IPSCs to date is achieved. Furthermore, the successful fabrication of a p–i–n type monolithic inorganic perovskite/silicon TSCs with an efficiency of 25.31% for the first time is demonstrated. Crucially, the unencapsulated ABA-treated IPSCs shows enhanced photostability, retaining 80.33% of its initial efficiency after 270 h, and thermal stability (maintain 85.98% of its initial efficiency after 300 h at 65 °C). The unencapsulated ABA-treated TSCs also retains 92.59% of its initial efficiency after 200 h under continuous illumination in ambient air.

Nature Energy, Published online: 13 April 2023; doi:10.1038/s41560-023-01251-6

A mild continuous pH control strategy is applied to regulate the hydrolysis of TiCl₄ post-treatment on TiO₂ film by urea. A uniform anatase-dominated TiO₂ layer is formed on the mesoporous TiO₂, resulting in reduced defect density and superior band energy level. The efficiency of carbon-based perovskite solar cells is improved from 16.63% to 18.08%.

Abstract

Titanium oxide (TiO₂) has been widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs). Typically, TiCl₄ post-treatment is indispensable for modifying the surfaces of TiO₂ ETL to improve the electron transport performance. However, it is challenging to produce the preferred anatase phase-dominated TiO₂ by the TiCl₄ post-treatment due to the higher thermodynamic stability of the rutile phase. In this work, a mild continuous pH control strategy for effectively regulating the hydrolysis process of TiCl₄ post-treatment is proposed. As the weak organic base, urea has been demonstrated can maintain a moderate pH decrease during the hydrolysis process of TiCl₄ while keeping the hydrolysis process relatively mild due to the ultra-weak alkalinity. The improved pH environment is beneficial for the formation of anatase TiO₂. Consequently, a uniform anatase-dominated TiO₂ surface layer is formed on the mesoporous TiO₂, resulting in reduced defect density and superior band energy level. The interfacial charge recombination is effectively suppressed, and the charge extraction efficiency is improved simultaneously in the fabricated solar cells. The efficiency of the fabricated carbon electrode-based PSCs (C-PSCs) is improved from 16.63% to 18.08%, which is the highest for C-PSCs based on wide-bandgap perovskites.