JIALINGBO

Dibenzo[g,p]chrysene, a non-planar double helicene, displays enhanced rigidity compared to tetraphenylethene, enabling the development of a molecular semiconductor with elevated cohesive energy density and hole mobility. Applied in high-efficiency perovskite solar cell fabrication, it exhibits remarkable operational stability at 45 °C and storage stability at 85 °C.

Abstract

Efficient and robust n-i-p perovskite solar cells necessitate superior organic hole-transport materials with both mechanical and electronic prowess. Deciphering the structure–property relationship of these materials is crucial for practical perovskite solar cell applications. Through direct arylation, two high glass transition temperature molecular semiconductors, DBC-ETPA (202 °C) and TPE-ETPA (180 °C) are synthesized, using dibenzo[g,p]chrysene (DBC) and 1,1,2,2-tetraphenylethene (TPE) tetrabromides with triphenylene–ethylenedioxythiophene-dimethoxytriphenylamine (ETPA). In comparison to spiro-OMeTAD, both semiconductors exhibit shallower HOMO energy levels, resulting in increased hole densities (generated by air oxidation doping) and accelerated hole extraction from photoexcited perovskite. Experimental and theoretical studies highlight the more rigid DBC core, enhancing hole mobility due to reduced reorganization energy and lower energy disorder. Importantly, DBC-ETPA possesses a higher cohesive energy density, leading to lower ion diffusion coefficients and higher Young's moduli. Leveraging these attributes, DBC-ETPA is employed as the primary hole-transport layer component, yielding perovskite solar cells with an average efficiency of 24.5%, surpassing spiro-OMeTAD reference cells (24.0%). Furthermore, DBC-ETPA-based cells exhibit superior operational stability and 85 °C thermal storage stability.

In this study, to overcome the wettability issue of highly hydrophobic self-assembled monolayer (SAM), a new SAM deposition method based on a vacuum-assisted deposition (VD) process was attempted. The VD process improved the performance of PSCs by improving the wettability of the hydrophobic SAM layer. This finding can provide a cornerstone for using highly hydrophobic SAM-based hole transport layer.

Recently, various carbazole-based self-assembled monolayers (SAMs) have been investigated for use in the hole transport layer (HTL) of perovskite solar cells (PSCs). In particular, [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) is attracting attention as an HTL for high-efficiency PSC due to its potential for high open-circuit voltage (V _OC) and fill factor (FF). However, Me-4PACz has strong hydrophobicity due to its methyl group (–CH₃) and long alkyl chain (C4H₈), which makes it difficult to deposit a high-quality perovskite layer on top of conventionally coated Me-4PACz. In this study, to overcome these limitations, a new SAM deposition method based on a vacuum-assisted deposition (VD) process is attempted. As a result, a uniform perovskite layer is deposited on top of Me-4PACz through a very simple VD process, achieving 20.31% efficiency, which is not only close to the highest efficiency among Me-4PACz-based PSCs, but also improved long-term stability of the device. It is believed that the findings of this study can be a cornerstone for using SAM-based HTL with high hydrophobicity in the future.

Large-area near-infrared-transparent perovskite mini-modules with excellent uniformity and minimal spread in device performance achieve with fully scalable process by employing bilayer hole transport layer stack of sputtered NiO and blade-coated MeO-2PACz. In combination with CIGS bottom module, fully scalable 4-terminal perovskite-CIGS tandem modules with 20.5% power conversion efficiency are demonstrated.

The use of carbazole-based self-assembled monolayer (SAM) as a hole transport layer (HTL) has led to the efficiency advancement in p–i–n perovskite solar cells (PSCs). However, PSCs with SAM HTL display a large spread in device performance even on small-area substrates owing to poor SAM surface coverage and dewetting of the perovskite ink. Efforts to improve the uniformity in device performance of SAM-based PSCs have been confined to spin-coating method, which lacks high-throughput capabilities and leads to excessive material wastage. Herein, a scalable bilayer HTL stack with sputtered NiO and blade-coated SAM is utilized to achieve improved SAM coverage and accomplish uniform coating of perovskite absorber on 5 cm × 5 cm substrates. Fully scalable p–i–n PSCs with efficiency close to 19% with a minimal spread in device performance are achieved. To showcase the upscaling potential, near-infrared-transparent perovskite mini-modules with efficiency close to 15% and 13% are achieved on an aperture area of 2.56 and 12.96 cm². Together with low-bandgap (1.0–1.1 eV) Cu(In,Ga)Se₂ (CIGS) mini-modules, the first fully scalable 4-terminal perovskite-CIGS tandem mini-module with an efficiency of 20.5% and 16.9% on an aperture area of 2.03 and 10.23 cm² is demonstrated.

Self-assembled monolayers (SAM) modified nickel oxide (NiO_x) is used as a hole-selective layer in inverted perovskite solar cells and finally, the highest power conversion efficiency of 24.8% is achieved with excellent thermal stability by the highest coverage of SAM on NiO_x.

Abstract

Nickel oxide is one of the most promising hole-transporting materials in inverted perovskite solar cells (PSCs) but suffers from undesired reactions with perovskite which leads to limited device performance and stability. Self-assembled monolayers (SAMs) are demonstrated to effectively optimize the NiO_x/perovskite interface, but the significance of the compactness of the SAM at the interface is less investigated. Here, a series of methoxy-substituted triphenylamine functionalized benzothiadiazole (TBT) based SAM molecules, TBT-BA, TBT-FBA, and TBT-DBA, with benzoic acid, 2-fluorobenzoic acid and isophthalic acids as anchoring groups are used to modify NiO_x. TBT-BA with the simplest structure is demonstrated to form the densest SAM on NiO_x, thus optimized NiO_x/SAM/perovskite interface is achieved with enhanced charge collection and suppressed interfacial reaction and recombination. TBT-BA can also passivate the perovskite most effectively due to the highest binding energy toward perovskite, thus the corresponding inverted PSCs show the highest PCE of 24.8% and maintain 88.7% of the initial PCE after storage at 60 °C for 2635 h in the glovebox. The work provides important insights into designing SAM molecules for modification transporting layers for efficient and stable PSCs.

This work reports a photochemistry-based p-doping mechanism of spiro-OMeTAD. Metal cations (Y3+ or La3+)-tBP complexes catalyze the fast quenching of photo-excited spiro-OMeTAD via a symmetry-breaking charge separation process. This photo-doping method yields spiro-OMeTAD+ through the oxidation of spiro anions by trace of oxidizer. This photo-doping method can prevent unintended oxidation and dopant-mediated degradation due to no additional aging or ion penetration. The photo-doped perovskite solar cell shows far superior operational stability and maintains excellent efficiency under full sun illumination over 1,000 h.

By employing a ligand exchange strategy with (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB), the authors capitalized on lead-sulfur (Pb−S) interactions. MUTAB passivates the nanocrystal (NC) surface, ensuring water dispersibility and stability, unlike oleyl amine/oleic acid (OAm/OAc)-capped counterparts prone to rapid degradation. The optoelectronic properties of MUTAB-stabilized NCs are validated through efficient 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation under visible light irradiation.

Abstract

Lead halide perovskite nanocrystals (LHP NCs) have garnered attention as promising light-harvesting materials for optoelectronics and photovoltaic devices, attributed to their impressive optoelectronic properties. However, their susceptibility to moisture-induced degradation has hindered their practical applications. Despite various encapsulation strategies, challenges persist in maintaining their stability and optoelectronic performance simultaneously. Here, a ligand exchange approach is proposed using (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide (MUTAB) to enhance the stability and dispersibility of CsPbBr₃ (CPB) NCs in aqueous environments. MUTAB enables effective surface passivation of the CPB NCs via robust Pb–S interactions at the S-terminal while concurrently directing water molecules through the unbound cationic N-terminal or vice versa, ensuring water dispersibility and stability. Spectroscopic analysis confirms retained structural and optical integrity post-ligand exchange. Crucially, MUTAB-bound CPB NCs exhibit sustained charge transfer properties, demonstrated by aqueous colloidal oxidation reactions. This ligand exchange strategy offers a promising pathway for advancing LHP NCs toward practical optoelectronic and photocatalytic applications.

Blue perovskite quantum dot-based light-emitting diode (QLED) with an external quantum efficiency (EQE) of 23.5% at 490 nm is achieved through a combination of quantum dot (QD) passivated by trifluoroacetate and optimal device design through a mixed hole-transport layer. The work breaks through the EQE gap of 20% for blue perovskite-based QLEDs and significantly promotes their commercialization process.

Abstract

Perovskite quantum dot-based light-emitting diodes (QLEDs) have been considered a promising display technology due to their wide color gamut for authentic color expression. Currently, the external quantum efficiency (EQE) for state-of-the-art blue perovskite QLEDs is about 15%, which still lags behind its green and red counterparts (>25%) and blue film-based LEDs. Here, blue perovskite QLEDs that achieve an EQE of 23.5% at 490 nm is presented, to the best knowledge, which is the highest value reported among blue perovskite-based LED fields. This impressive efficiency is achieved through a combination of quantum dot (QD) passivation and optimal device design. First, blue mixed halide perovskite CsPbCl_{3− x} Br _x QDs passivated by trifluoroacetate exhibit excellent exciton recombination behavior with a photoluminescence quantum yield of 84% due to reducing uncoordinated Pb surface defects. Furthermore, the device is designed by introducing a mixed hole-transport layer (M-HTL) to increase hole injection and transportation capacity and improve carrier balance. It is further found that M-HTL can decrease carrier leakage and increase radiative recombination in the device, evidenced by the visual electroluminescence spectrum at 2.0 V. The work breaks through the EQE gap of 20% for blue perovskite-based QLEDs and significantly promotes their commercialization process.

The study reports the synthesis of the first crystalline 2D fullerene-based metal halide semiconductor, namely (C₆₀-2NH₃)Pb₂I₆. Utilization of the C₆₀-2NH₃I₂ adduct as an interfacial layer in mixed Pb-Sn perovskite solar cells substantially improved both carrier transport and device stability. This work sets the foundation for the development of a new family of multifunctional materials, namely Fullerene Metal Halide Semiconductors.

Abstract

Despite advances in mixed tin-lead (Sn-Pb) perovskite-based solar cells, achieving both high-efficiency and long-term device stability remains a major challenge. Current device deficiencies stem partly from inefficient carrier transport, originating from defects and improper band energy alignment among the device's interfaces. Developing multifunctional interlayer materials simultaneously addressing the above concerns poses an excellent strategy. Herein, through molecular and crystal engineering, an amine-functionalized C₆₀ mono-adduct derivative (C₆₀-2NH₃ = bis(2-aminoethyl) malonate-C₆₀) is utilized for the synthesis of the first crystalline fullerene-based 2D metal halide semiconductor, namely (C₆₀-2NH₃)Pb₂I₆. Single crystal XRD studies elucidated the structure of the new material, while DFT calculations highlighted the strong contribution of C₆₀-2NH₃ to the electronic density of states of the conduction band of (C₆₀-2NH₃)Pb₂I₆. Utilization of C₆₀-2NH₃ as an interlayer between a FA_0.6MA_0.4Pb_0.7Sn_0.3I₃ perovskite and a C₆₀ layer offered superior band energy alignment, reduced nonradiative recombination, and enhanced carrier mobility. The corresponding perovskite solar cell (PSC) device achieved a power conversion efficiency (PCE) value of 21.64%, maintaining 90% of its initial efficiency, after being stored under a N₂ atmosphere for 2400 h. This work sets the foundation for developing a new family of functional materials, namely Fullerene Metal Halide Semiconductors, targeting applications from photovoltaics to catalysis, transistors, and supercapacitors.

A facile and eco-friendly dimethyl sulfoxide-mediated solution aging (DMSA) treatment is proposed to homogenize the morphology and composition of methylammonium-free wide-bandgap perovskite films, which contributes to highly efficient and stable semitransparent perovskite solar cells and tandem solar cells.

Abstract

A facile and eco-friendly dimethyl sulfoxide-mediated solution aging (DMSA) treatment is presented to control the crystallization dynamics of methylammonium (MA)-free wide-bandgap (WBG) perovskite films, enhancing film quality, and morphology for high-performance tandem solar cells. The comprehensive structural, morphological, and characterization analyses reveal that the DMSA treatment significantly enhances composition and morphology homogeneity while suppressing halide segregation. Consequently, opaque, and semi-transparent MA-free WBG perovskite solar cells (PSCs) exhibit remarkable power conversion efficiencies (PCEs) of 18.28% and 17.61%, respectively. Notably, the unencapsulated DMSA-treated devices maintain 95% of the initial PCE after 900 h of continuous operation at 55 °C ± 5 °C. Furthermore, stacking semi-transparent DMSA-treated PSCs as top cells in a 4T tandem configuration, along with silicon heterojunction (SHJ), lead–tin (Pb–Sn) alloyed PSCs, and organic photovoltaics (OPV) as bottom cells, yields impressive PCEs of 28.09%, 26.09%, and 25.28%, respectively, for the fabricated tandem cells. This innovative approach opens new avenues for enhancing the photo-stability and photovoltaic performance of perovskite-based tandem solar cells.

Self-assembled monolayer (SAM) molecules are extensively employed in perovskite solar cells, serving both as charge transport materials and interfacial modulators. These molecules play a crucial role in adjusting surface energy levels, reducing interfacial trap defects, and enhancing perovskite crystallization quality, thereby leading to improved performance and stability of perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) hold significant promise as the next-generation materials in photovoltaic markets, owing to their ability to achieve impressive power conversion efficiencies, streamlined fabrication processes, cost-effective manufacturing, and numerous other advantages. The utilization of self-assembled monolayer (SAM) molecules has proven to be a significant success in enhancing device efficiency and extending device stability. This review highlights the dual use of SAM molecules in the realm of PSCs, which can not only serve as charge transport materials but also act as interfacial modulators. These research endeavors encompass a wide range of applications for various SAM molecules in both n-i-p and p-i-n structured PSCs, providing a deep insight into the underlying mechanisms. Furthermore, this review proposes current research challenges for future investigations into SAM materials. This timely and thorough review seeks to provide direction and inspiration for current research efforts dedicated to the ongoing incorporation of SAMs in the field of perovskite photovoltaics.

A new all-perovskite tandem solar cell structure, with 3T back-contact all-perovskite tandem solar cell structure effectively avoids the current matching of 2T tandem solar cell and the light loss of 4T tandem solar cell. The feasibility of the 3T back-contact all-perovskite tandem solar cell is verified by the simulation method.

Abstract

The development of efficient all perovskite tandem solar cells has faced challenges related to current matching and optical losses. In this work, a design of a non-coplanar three-terminal (3T) all perovskite tandem solar cell is presented, which consists of a p-i-n inverted NiO_X-based CsPbI₂Br perovskite top cell, and a FA_0.6MA_0.4Sn_0.5Pb_0.5I₃ perovskite bottom cell with back-contact (BC) device structure. It effectively mitigated the optical losses introduced in non-absorbing layers and resulted in a 2.9% absolute efficiency improvement compared to that of planar sandwich-type 3T tandems. Both optical and electrical characteristics of the multi-terminal tandem cells are investigated. Then, it is focused on understanding the impact of top cell thickness on overall non-coplanar BC 3T-tandem performance, considering low-energy photon optical reflection and carrier transport distance. Following optimizations of energy level and device structure, an efficiency of 32.16% is achieved, with non-coplanar BC 3T device architecture: top cell consisting of hole extraction layer (ITO/NiOx), CsPbI₂Br absorber layer, and electron extraction layer (ZnO/FA_0.6MA_0.4Sn_0.5Pb_0.5I₃/SnO₂/Ag); and bottom cell (Ni/NiOx/FA_0.6MA_0.4Sn_0.5Pb_0.5I₃/SnO₂/Ag); bottom perovskite layer has two functions, one is electron transport layer for top cell, and the other is low-energy photon absorption layer in bottom cell. It provides insight and a promising pathway for manufacturing high-efficient all perovskite tandem solar cells.

2D/3D wide-bandgap perovskites are successfully constructed using 1-TzFACl as a spacer. The 2D/3D perovskite exhibits better film quality, enhanced crystallinity, and suppressed nonradiative recombination losses. The optimized device based on 2D/3D perovskite shows an efficiency of 21.58% with enhanced phase stability. An efficiency of 25.66% and improved light stability are achieved for monolithic 2-terminal perovskite/silicon tandem solar cells.

To maximize the power conversion efficiency (PCE) and stability of perovskite/silicon tandem solar cells (TSCs), high-performance and stable perovskite top cells with wide-bandgaps are required. A 2D/3D wide-bandgap perovskite with a bandgap of 1.69 eV using 1H-1,2,4-triazole-1-carboximidamide (1-TzFACl) as a spacer is developed. The 2D/3D wide-bandgap perovskite shows better film quality, enhanced crystallinity, suppressed nonradiative recombination, and significantly improved phase stability. Its initial PCE (21.58%) remains above 87% after 1560 h of continuous illumination due to the insertion of Cl⁻ in the perovskite lattice. A monolithic two-terminal perovskite/silicon TSC achieves a PCE of 25.66% with high light stability. This work provides an ingenious strategy to restrain the phase segregation in wide-bandgap perovskites, leading to effective and stable perovskite/silicon TSCs.

In recent years, self-assembled monolayers (SAMs) have been investigated as a fascinating hole-selective contact for inverted positive-intrinsic-negative (p-i-n) perovskite solar cells (IPSCs). Here, the rapid progress of the IPSCs based on SAMs is comprehensively reviewed from the aspects of efficiency and stability progress, device up-scaling issues, and cost analysis.

Abstract

Inverted positive-intrinsic-negative (p-i-n) perovskite solar cells (IPSCs) have attracted widespread attention due to their low fabrication temperature, good stability in ambient air, and the potential for use in flexible and tandem devices. In recent years, self-assembled monolayers (SAMs) have been investigated as a promising hole-selective contact for IPSCs, leading to an impressive record efficiency of about 26%, which is comparable to that of the regular n-i-p counterparts. This review focuses on the progress of SAM-based IPSCs from the perspective of energy level matching, defect passivation, interface carrier extraction, and SAMs’ stability improvement, as well as the advances in up-scalable fabrication of SAMs and perovskite layers for efficient solar modules and tandem devices. A cost analysis of the SAMs and other commonly used hole-selective materials is conducted to evaluate their cost-effectiveness for photovoltaic applications. Finally, the future challenges are pointed out and the perspectives on how to up-scale SAM-based IPSCs and improve their long-term operational stability are provided.

The introduction of choline acetate alongside the perovskite precursors triggers the formation of a 1D/3D perovskite heterojunction at the buried interface of the active layer. Due to enhanced homogeneity, defect passivation, and improved interfacial energy alignment, inverted architecture perovskite solar cells reach a maximum photovoltaic efficiency of >24% with improved stability.

Abstract

Interfacial modification is a key strategy for improving the performance of perovskite photovoltaic devices. While the modification of the top surface of the perovskite active layer is well established, engineering of the buried interface is highly challenging. Here, the spontaneous formation of a 1D/3D perovskite heterojunction at the buried interface of a perovskite active layer by incorporating choline acetate alongside the perovskite precursors is reported. Importantly, extensive spectroscopic and microscopic characterization and solid-state nuclear magnetic resonance experiments demonstrate the formation of phase-pure 1D and 3D domains. The 1D/3D junction results in a suppression of the defect states and an improved energetic level alignment at the buried interface, leading to a maximum power conversion efficiency of >24% when incorporated in inverted architecture perovskite solar cells. This work introduces a versatile approach to the modification of the buried interface of the perovskite active layer.

A unique intermediate phase engineering strategy is developed to overcome the residual of solvent in unannealed perovskite film by introducing octane-1,8-diamine dihydroiodide. This helps to achieve single junction wide bandgap perovskite solar cells with high efficiency >22% and outstanding stability, and achieve high performance 4-terminal all perovskite and large area perovskite solar cells.

Abstract

Wide bandgap (WBG) perovskite can construct tandem cells with narrow bandgap solar cells by adjusting the band gap to overcome the Shockley−Queisser limitation of single junction perovskite solar cells (PSCs). However, WBG perovskites still suffer from severe nonradiative carrier recombination and large open-circuit voltage loss. Here, this work uses an in situ photoluminescence (PL) measurement to monitor the intermediate phase evolution and crystallization process via blade coating. This work reports a strategy to fabricate efficient and stable WBG perovskite solar cells through doping a long carbon chain molecule octane-1,8-diamine dihydroiodide (ODADI). It is found that ODADI doping not only suppresses intermediate phases but also promote the crystallization of perovskite and passivate defects in blade coated 1.67 eV WBG FA_0.7Cs_0.25MA_0.05Pb(I_0.8Br_0.2)₃ perovskite films. As a result, the champion single junction inverted PSCs deliver the efficiencies of 22.06% and 19.63% for the active area of 0.07 and 1.02 cm², respectively, which are the highest power conversion efficiencies (PCEs) in WBG PSCs by blade coating. The unencapsulated device demonstrates excellent stability in air, which maintains its initial efficiency at the maximum power points under constant AM 1.5G illumination in open air for nearly 500 h. The resulting semitransparent WBG device delivers a high PCE of 20.06%, and the 4-terminal all-perovskite tandem device delivers a PCE of 28.35%.

A top-down engineering strategy of perovskite crystallization is introduced via propylamine chloride (PACl) post treatment of perovskite wet film, inducing downward preferred crystallization orientation and realizing excellent homogeneity in terms of vertical and horizontal scale of perovskite, contributing to a champion PCE of 25.07% for p-i-n PVSCs, as well as the enhanced thermal and operational stability.

Abstract

Crystallization orientation plays a crucial role in determining the performance and stability of perovskite solar cells (PVSCs), whereas effective strategies for realizing oriented perovskite crystallization is still lacking. Herein, a facile and efficient top-down strategy is reported to manipulate the crystallization orientation via treating perovskite wet film with propylamine chloride (PACl) before annealing. The PA⁺ ions tend to be adsorbed on the (001) facet of the perovskite surface, resulting in the reduced cleavage energy to induce (001) orientation-dominated growth of perovskite film and then reduce the temperature of phase transition, meanwhile, the penetrating Cl ions further regulate the crystallization process. As-prepared (001)-dominant perovskite films exhibit the ameliorative film homogeneity in terms of vertical and horizontal scale, leading to alleviated lattice mismatch and lowered defect density. The resultant PVSC devices deliver a champion power conversion efficiency (PCE) of 25.07% with enhanced stability, and the unencapsulated PVSC device maintains 95% of its initial PCE after 1000 h of operation at the maximum power point under simulated AM 1.5G illumination.

In this work, we reveal the existence of a built-in potential at the homojunction interface of the perovskite film near the electron-transporting SnO2 layer. Adjusting the energy-level alignment at this interface is found to play a critical role in mitigating ion migration, which eventually enhances photovoltaic performance and stability.

Publication date: May 2024

Source: Nano Energy, Volume 123

Author(s): Mengqi Jin, Chong Chen, Fumin Li, Zhitao Shen, Hu Shen, Dong Yang, Huilin Li, Ying Liu, Chao Dong, Rong Liu, Mingtai Wang

Inverted perovskite solar cells (PSCs) have both excellent stability and continuously broken-through efficiencies. Herein, the characteristics of inverted PSCs including each functional layers, interfacial regulation strategies, and device stability are summarized. Meanwhile, the applications of inverted structure in tandem and flexible photovoltaic devices, and modules are introduced. Finally, the remaining challenges and several proposals of PSCs are put forward.

Abstract

Perovskite solar cells (PSCs) have attracted widespread research and commercialization attention because of their high power conversion efficiency (PCE) and low fabrication cost. The long-term stability of PSCs should satisfy industrial requirements for photovoltaic devices. Inverted PSCs with a p-i-n architecture exhibit considerable advantages because of their excellent stability and competitive efficiency. The continuously broken-through PCE of inverted PSCs shows huge application potential. This review summarizes the developments and outlines the characteristics of inverted PSCs including charge transport layers (CTLs), perovskite compositions, and interfacial regulation strategies. The latest effective CTLs, interfacial modification, and stability promotion strategies especially under light, thermal, and bias conditions are emphatically analyzed. Furthermore, the applications of the inverted structure in high-efficiency and stable tandem, flexible photovoltaic devices, and modules and their main obstacles are systematically introduced. Finally, the remaining challenges faced by inverted devices are discussed, and several directions for advancing inverted PSCs are proposed according to their development status and industrialization requirements.

An anti-solvent-free (ASF) technique is devised to fabricate photostable pure-iodide wide-bandgap perovskite solar cells (PSCs). Compared with wide-bandgap PSCs made from anti-solvent process, the ASF method significantly improves the device performance and reproducibility. Furthermore, methylammonium chloride is applied to enhance the crystallinity. Consequently, the ASF-based PSCs deliver a highest PCE of 21.30 % with excellent photostability.

Abstract

The perovskite/silicon tandem solar cell (TSC) has attracted tremendous attention due to its potential to breakthrough the theoretical efficiency set for single-junction solar cells. However, the perovskite solar cell (PSC) designed as its top component cell suffers from severe photo-induced halide segregation owing to its mixed-halide strategy for achieving desirable wide-bandgap (1.68 eV). Developing pure-iodide wide-bandgap perovskites is a promising route to fabricate photostable perovskite/silicon TSCs. Here, we report efficient and photostable pure-iodide wide-bandgap PSCs made from an anti-solvent-free (ASF) technique. The ASF process is achieved by mixing two precursor solutions, both of which are capable of depositing corresponding perovskite films without involving anti-solvent. The mixed solution finally forms Cs_0.3DMA_0.2MA_0.5PbI₃ perovskite film with a bandgap of 1.68 eV. Furthermore, methylammonium chloride additive is applied to enhance the crystallinity and reduce the trap density of perovskite films. As a result, the pure-iodide wide-bandgap PSC delivers efficiency as high as 21.30 % with excellent photostability, the highest for this type of solar cells. The ASF method significantly improves the device reproducibility as compared with devices made from other anti-solvent methods. Our findings provide a novel recipe to prepare efficient and photostable wide-bandgap PSCs.

Recent progress on the influence of pressure on perovskite materials and devices is reviewed. Based on the mechanism of influence, the pressure effect can be divided into six categories: crystal densification, crystal orientation, crystal size, bond length, bond angle, bandgap, phase transition, and amorphous phase. Finally, prospects for developing new perovskite structures and devices under pressure are presented.

Abstract

As a fundamental thermodynamic parameter, pressure serves as an effective tool to control the structures and properties of functional materials. To date, numerous pressure-engineering methods have been introduced to enhance perovskite structures and devices. This paper comprehensively reviews the advances in understanding the effects of pressure on perovskite materials and devices, encompassing both low and high-pressure influences. These effects are categorized into six distinct groups based on their underlying mechanisms, detailing the evolution of perovskite structures from macroscopic to microscopic levels, and exploring the interplay between these structures and their functional characteristics. Finally, the current challenges and offer insights into the future prospects for harnessing pressure effects to further develop perovskite structures, properties, and devices are assessed.

Py-DB with an extended conjugated structure is an effective dopant-free HTM when applied in n-i-p-type PSCs, affording an efficiency of 24.33 %, the highest PCE for a dopant-free small-molecule HTM.

Abstract

Dopant-free hole transporting materials (HTMs) is significant to the stability of perovskite solar cells (PSCs). Here, we developed a novel star-shape arylamine HTM, termed Py-DB, with a pyrene core and carbon-carbon double bonds as the bridge units. Compared to the reference HTM (termed Py-C), the extension of the planar conjugation backbone endows Py-DB with typical intermolecular π–π stacking interactions and excellent solubility, resulting in improved hole mobility and film morphology. In addition, the lower HOMO energy level of the Py-DB HTM provides efficient hole extraction with reduced energy loss at the perovskite/HTM interface. Consequently, an impressive power conversion efficiency (PCE) of 24.33 % was achieved for dopant-free Py-DB-based PSCs, which is the highest PCE for dopant-free small molecular HTMs in n-i-p configured PSCs. The dopant-free Py-DB-based device also exhibits improved long-term stability, retaining over 90 % of its initial efficiency after 1000 h exposure to 25 % humidity at 60 °C. These findings provide valuable insights and approaches for the further development of dopant-free HTMs for efficient and reliable PSCs.

Nature Communications, Published online: 05 March 2024; doi:10.1038/s41467-024-46145-7

The development of robust quasi-ohmic contact with minimal resistance, exceptional stability and cost-effectiveness is crucial for practical application of perovskite solar cells. Here, authors report a polymer-acid-metal structure as the contact and realize long photo-thermal-operational stability.

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.

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.