Suppressing the Photoinduced Halide Segregation in Wide-Bandgap Perovskite Solar Cells by Strain Relaxation

Efficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light-induced phase segregation of WBG perovskite result in large open-circuit voltage (V_OC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis-base trans-Ferulic acid (t-FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light-induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of V_OC. Moreover, replacing a mixture of MeO-2PACZ and Me-4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and V_OC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin-coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite-based tandem devices.     

Highly Efficient and Stable Wide-Bandgap Perovskite Solar Cells via Strain Management

Wide-bandgap (WBG) perovskite solar cells (PSCs) with high performance and stability are in considerable demand to boost tandem solar cell efficiencies. Perovskite bandgap broadening results in a high barrier for enhancing the efficiency of PSCs and phase segregation in perovskite. In this study, it is shown that the residual strain is the key factor affecting the WBG perovskite device efficiency and stability. The dimethyl sulfoxide addition helps lead halide with opening the layer spacing to form intermediate phases that provide more nucleation sites to eliminate lattice mismatch with organic components, which dominates the strain effects on the WBG perovskite growth in a sequential deposition. By minimizing the strain, 1.67 and 1.77 eV nip devices with record efficiencies of 22.28% and 20.45%, respectively, can be achieved. The greatly suppressed phase segregation enables the devices with retained 90–95% of initial efficiency over 4000 h of damp stability and 80–90% of initial efficiency over 700 h of maximum-power-point (MPP) stability. Besides, the 1.67 eV pin devices can achieve a competitive 22.3% efficiency with considerable damp-heat, pre-ultraviolet (pre-UV) aging and MPP tracking stability according to IEC 61215. The final efficiency of more than 28.3% for the perovskite/Si tandem is obtained.     

Efficient and Stable Inverted Wide-Bandgap Perovskite Solar Cells and Modules Enabled by Hybrid Evaporation-Solution Method

Wide-bandgap perovskite solar cells (WBG-PSCs), when partnered with Si bottom cells in tandem configuration, can provide efficiencies up to 44%; yet, the development of stable, efficient, and scalable WBG-PSCs is required. Here, the utility of the hybrid evaporation-solution method (HESM) is investigated to meet these demanding requirements via its unique advantages including ease of control and reproducibility. A PbI₂/CsBr layer is co-evaporated followed by coating of organic-halide solutions in a green solvent. Bandgaps between 1.55–1.67 eV are systematically screened by varying CsBr and MABr content. Champion efficiencies of 21.06% and 20.35% in cells and 19.83% and 18.73% in mini-modules (16 cm²) for perovskites with 1.64 and 1.67 eV bandgaps are achieved, respectively. Additionally, 18.51%-efficient semi-transparent WBG-PSCs are implemented in 4T perovskite/bifacial silicon configuration, reaching a projected power output of 30.61 mW cm⁻² based on PD IEC TS 60904-1-2 (BiFi200) protocol. Despite similar bandgaps achieved by incorporating Br via MABr solution and/or CsBr evaporation, PSCs having a perovskite layer without MABr addition show significantly higher thermal and moisture stability. This study proves scalable, high-performance, and stable WBG-PSCs are enabled by HESM, hence their use in tandems and in emerging applications such as indoor photovoltaics are now within reach.     

Enhancing Efficiency and Intrinsic Stability of Large-Area Blade-Coated Wide-Bandgap Perovskite Solar Cells Through Strain Release

The realization of efficient large-area perovskite solar cells stands as a pivotal milestone for propelling their future commercial viability. However, the upscaling fabrication of perovskite solar cells is hampered by efficiency losses, and the underlying growth mechanism remains enigmatic. Here, it is unveiled that a prevalent upscaling technology, namely blade-coating, inherently triggers top-down inhomogeneity strains, predominantly concentrated on the surface of wide-bandgap perovskite films. Through strain mitigation strategies, the perovskite films exhibit reduced halide vacancies, leading to enhanced stability and improved optoelectronic characteristics. Consequently, the blade-coated perovskite solar cells achieve minimal efficiency loss when transitioning from small-area to large-area devices, enabling the realization of 1 cm²-area 1.77 eV-bandgap cells with a remarkable efficiency of 18.71%. Additionally, the strain-relieved device exhibits an exceptional 109% retention of its initial efficiency even after 400 h of continuous operation, in stark contrast to the control device which experiences a decline to 91%. Furthermore, the resulting 4-terminal all-perovskite tandem solar cells crafted utilizing blade-coated 1.77 eV-bandgap subcells achieve a maximum efficiency of 27.64% (stabilized at 27.28%). This study not only sheds light on the intricacies of upscaling preparation techniques but also overcomes potential obstacles that can impede the trajectory toward achieving large-scale perovskite solar cells.     

有机卤化物盐对钙钛矿太阳电池器件性能的影响

有机无机杂化钙钛矿已被证明是优良的光吸收材料,可用于高效率光伏领域。增大钙钛矿薄膜的晶粒尺寸和对晶界缺陷的钝化是提高太阳电池性能的重要途径。文章报道了一种简单的缺陷钝化技术,将有机卤化物盐BAI引入钙钛矿的混合阳离子中,以起到增大晶粒和钝化缺陷的作用,使钙钛矿太阳电池的光电转换效率从19.46%提升至21.56%。这种效率的提升是在不损失短路电流和填充因子的情况下,开路电压从1.04V提高到1.11V的结果。这种提升钙钛矿型太阳电池开路电压的方法,为进一步提高钙钛矿型太阳电池的光电性能提供了新的途径。     

In Situ Growth of 2D Perovskite Capping Layer for Stable and Efficient Perovskite Solar Cells

2D halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultrastable 2D Ruddlesden–Popper PSCs still lag far behind their traditional 3D perovskite counterparts. Here, a rationally designed 2D‐3D perovskite stacking‐layered architecture by in situ growing 2D PEA₂PbI₄ capping layers on top of 3D perovskite film, which drastically improves the stability of PSCs without compromising their high performance, is reported. Such a 2D perovskite capping layer induces larger Fermi‐level splitting in the 2D‐3D perovskite film under light illumination, resulting in an enhanced open‐circuit voltage (V_oc) and thus a higher efficiency of 18.51% in the 2D‐3D PSCs. Time‐resolved photoluminescence decay measurements indicate the facilitated hole extraction in the 2D‐3D stacking‐layered perovskite films, which is ascribed to the optimized energy band alignment and reduced nonradiative recombination at the subgap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D‐3D PSCs show significantly improved long‐term stability, retaining nearly 90% of the initial power conversion efficiency after 1000 h exposure in the ambient conditions with a high relative humidity level of 60 ± 10%.     

Efficient Cesium Lead Halide Perovskite Solar Cells through Alternative Thousand‐Layer Rapid Deposition

The novel growth of cesium lead halide perovskite thin films, which are prepared through thousand‐layer rapid alternative deposition, is performed by developing an active perovskite film consisting of a layer‐by‐layer structure. This method is considerably more difficult to be implemented from the solution process. The obtained thin film morphology and characteristics are distinguished from that of the traditional a few layers and two‐material codeposition. These alternative deposited perovskites are integrated with vacuum‐deposited carrier‐transporting layers and electrodes, and all vacuum‐sublimed perovskite solar cells exhibit an outstanding power conversion efficiency of 13.0%. The use of these devices for environmental light energy harvesting provides a power conversion efficiency of 33.9% under fluorescent light illumination of 1000 lux.     

Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All-Perovskite Tandem Solar Cells with Efficiency over 25%

This study is on the enhancement of the efficiency of wide bandgap (FA_0.8Cs_0.2PbI_1.8Br_1.2) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI₃ PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA_0.8Cs_0.2PbI_1.8Br_1.2 PSCs. It is found that the surface-modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA_0.8Cs_0.2PbI_1.8Br_1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs (E_g = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all-perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.     

Undoped Hole Transport Layer Toward Efficient and Stable Inorganic Perovskite Solar Cells

Numerous strategies have been practiced to improve the power conversion efficiency of CsPbI₂Br-based perovskite solar cells (PSCs), which definitely makes efficiency gradually approach the theoretical efficiency limit. However, sufficient device stability is still in urgent demand for commercialization, pushing to overcome some instability sources induced by hygroscopicity of spiro-OMeTAD and residual strain of perovskite layer. To address these issues, p-type semiconductor of PCPDTBT is used to replace spiro-OMeTAD, enabling dual functions of hole transport and strain regulation. On the one hand, undoped PCPDTBT performs excellent hole extraction and transport, while avoiding the perovskite degradation caused by the hygroscopicity of common additives. On the other hand, PCPDTBT assisted by a thermally spin-coating method compensates for the thermally-induced residual strain in perovskite layer owing to its high thermal expansion coefficient. Consequently, CsPbI₂Br-based PSCs with PCPDTBT layer achieve improved efficiency of 16.5% as well as enhanced stability. This study provides a simple and facile strategy to achieve efficient and stable CsPbI₂Br-based PSCs.     

Low‐Bandgap Mixed Tin‐Lead Perovskites and Their Applications in All‐Perovskite Tandem Solar Cells

Efficient organic–inorganic metal halide perovskite absorbers have gained tremendous research interest in the past decade due to their super optoelectronic properties and defect tolerance. Lead (Pb) halide perovskites enable highly efficient perovskite solar cells (PSCs) with a record power conversion efficiency (PCE) of over 23%. However, the energy bandgaps of Pb halide perovskites are larger than the optimal bandgap for single junction solar cells, governed by the Shockley–Queisser (SQ) radiative limit. Mixed tin (Sn)‐Pb halide perovskites have drawn significant attention, since their bandgap can be tuned to below 1.2 eV, which opens a door for fabricating all‐perovskite tandem solar cells that can break the SQ radiative limit. This review summarizes the development of low‐bandgap mixed Sn‐Pb PSCs and their applications in all‐perovskite tandem solar cells. Its aim is to facilitate the development of new approaches to achieve high efficiency low‐bandgap single‐junction mixed Sn‐Pb PSCs and all‐perovskite tandem solar cells.     

MXene-Interconnected Two-Terminal,Mechanically-Stacked Perovskite/Silicon Tandem Solar Cell with High Efficiency

Two-terminal, mechanically-stacked perovskite/silicon tandem solar cells offer a feasible way to achieve power conversion efficiencies (PCEs) of over 35%, provided that the state-of-the-art industrial silicon solar cells and perovskite solar cells (PSCs) are fully compatible with one another. Herein, two-terminal, mechanically-stacked perovskite/silicon tandem solar cells are developed by mechanically interconnecting semitransparent PSCs and TOPCon solar cells with a MXene interlayer. The semitransparent PSCs are made from wide-bandgap perovskite Cs_0.15FA_0.65MA_0.20Pb(I_0.80Br_0.20)₃ films. Furthermore, the co-additives KPF₆ and CH₃NH₃Cl(MACl) are employed to reduce grain boundaries and intragranular defects in the perovskite, boosting the PCE of the semitransparent PSCs to a record-high value of 20.96% under reverse scan (RS) through a reduction in non-radiative recombination probability. These optimized semitransparent PSCs are then employed in MXene-interconnected two-terminal, mechanically-stacked tandem solar cells. The enhanced interfacial carrier transportation, with minimal influence on light transmission, imparted by the MXene flakes allows the tandem solar cells to achieve a stabilized PCE of 29.65%. The tandem cells also exhibit acceptable operational stability and are able to retain ≈93% and 92% of their initial PCEs after 120 min of continuous illumination or storage in ambient air for 1000 h, respectively.     

Improved Air Stability of Tin Halide Perovskite Solar Cells by an N-Type Active Moisture Barrier

Tin halide perovskite solar cells are promising for the next generation of highly efficient photovoltaics. Their commercialization can be accelerated by increasing their stability in moisture and oxygen. Herein, an n-type organic molecule (IO-4Cl) is applied as an interlayer between the perovskite films and electron transport layers in p-i-n structured devices. The electron-rich indacenodithieno-[3,2-b]thiophene enhances electron transport, while the hydrocarbon side chains and rigid conjugated backbone isolate air. It is also shown that the C═O in IO-4Cl can coordinate with Sn²⁺ on perovskite films' surface and grain boundaries to enhance perovskite crystal stability. In addition, IO-4Cl slows down crystallization dynamics, resulting in lower non-radiation recombination. The moisture ingress in the perovskite films is tracked under high relative humidity (RH) and it is found that IO-4Cl can mitigate moisture infiltration. Finally, the devices with IO-4Cl maintain 95% of the initial power conversion efficiency after 1200 h of storage in a nitrogen-filled glovebox, and their stability in ambient air (60–80% RH) is significantly improved against pristine devices, thus demonstrating the beneficial effects of IO-4Cl interlayer on device stability.     

Bidirectional Targeted Therapy Enables Efficient,Stable, and Eco-Friendly Perovskite Solar Cells

Perovskite solar cells (PSCs) have witnessed rapid development toward commercialization based on their superior efficiency except for some remained misgivings about their poor stability primarily originating from interfacial problems. Robust back interface for neutralization of crystal defects, depression of dopant lithium ions (Li⁺) diffusion, and even inhibition of toxic lead (Pb) leakage is highly desirable; however, it remains a great challenge. Herein, a cost-effective interfacial therapy approach is developed to simultaneously alleviate the obstacles aforementioned. A small molecule, 1,4-dithiane with unique chair structure, is adapted to interact with under-coordinated Pb²⁺ on perovskite surface and Li⁺ from hole transport layer, neutralizing interfacial defects and suppressing Li⁺ diffusion. Besides, the presence of 1,4-dithiane can efficiently modulate interfacial energetics, enhance hydrophobicity of PSCs, and anchor Pb atoms via S Pb bond. Consequently, the target devices perform better than control devices when exposed to light-soaking, moisture, and thermal stress owing to the synergistic suppression of trap-state density, ions migration, and moisture permeation. The optimized target device delivers a champion efficiency of 23.27% with mitigated Pb leakage. This study demonstrates a promising functionalized modification strategy for constructing efficient, stable, and eco-friendly PSCs.     

Ambient Stable and Efficient Monolithic Tandem Perovskite/PbS Quantum Dots Solar Cells via Surface Passivation and Light Management Strategies

Here, highly efficient and stable monolithic (2-terminal (2T)) perovskite/PbS quantum dots (QDs) tandem solar cells are reported, where the perovskite solar cell (PSC) acts as the front cell and the PbS QDs device with a narrow bandgap acts as the back cell. Specifically, ZnO nanowires (NWs) passivated by SnO₂ are employed as an electron transporting layer for PSC front cell, leading to a single cell PSC with maximum power conversion efficiency (PCE) of 22.15%, which is the most efficient NWs-based PSCs in the literature. By surface passivation of PbS QDs by CdCl₂, QD devices with an improved open-circuit voltage and a PCE of 8.46% (bandgap of QDs: 0.92 eV) are achieved. After proper optimization, 2T and 4T tandem devices with stabilized PCEs of 17.1% and 21.1% are achieved, respectively, where the 2T tandem device shows the highest efficiency reported in the literature for this design. Interestingly, the 2T tandem cell shows excellent operational stability over 500 h under continuous illumination with only 6% PCE loss. More importantly, this device without any packaging depicts impressive ambient stability (almost no change) after 70 days in an environment with controlled 65% relative humidity, thanks to the superior air stability of the PbS QDs.     

Self‐Crystallized Multifunctional 2D Perovskite for Efficient and Stable Perovskite Solar Cells

Recently, perovskite solar cells (PSC) with high power‐conversion efficiency (PCE) and long‐term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in‐depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self‐crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self‐crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long‐term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) compared to the devices without the M2P.     

Reconstruction of the Indium Tin Oxide Surface Enhances the Adsorption of High-Density Self-Assembled Monolayer for Perovskite/Silicon Tandem Solar Cells

Self-assembled monolayers (SAMs) are widely used as carrier transport interlayers for enabling high-efficiency perovskite solar cells (PSCs). However, achieving uniform and pinhole-free monolayers on metal oxide (e.g., indium tin oxide, ITO) surfaces is still challenging due to the sensitivity of SAM adsorption to the complex oxide's surface chemistry. Here, the hydrofluoric acid and the subsequent UV–ozone treatment are employed to reconstruct the ITO surface by selectively removing the undesired terminal hydroxyl and hydrolysis product. This can significantly increase the ITO surface activity and area, thus facilitating the adsorption of high-density SAMs. The resultant fluorinated surface can also prevent the direct contact of ITO with the perovskite active layer and passivate the perovskite bottom interface. Benefiting from the synergistically improved perovskite film formation, charge extraction, energy level alignment, and interfacial chemical stability, the corresponding PSC achieves a greatly enhanced power conversion efficiency of 21.3%, along with an enhanced long-term stability as compared to the control counterpart. Furthermore, a semitransparent PSC with a certified efficiency of 19.0% (with a record fill factor of 84.1%) and a four-terminal perovskite/silicon tandem with an efficiency of 28.4% are also demonstrated.     

Inorganic Ammonium Halide Additive Strategy for Highly Efficient and Stable CsPbI3 Perovskite Solar Cells

All-inorganic perovskite cesium lead iodide (CsPbI₃) exhibits excellent prospects for commercial application as a light absorber in single-junction or tandem solar cells due to its outstanding thermal stability and proper bandgap. However, the device performance of CsPbI₃-based perovskite solar cells (PSCs) is still restricted by the unsatisfactory crystal quality and severe non-radiative recombination. Herein, inorganic additive ammonium halides are introduced into the precursor solution to regulate the nucleation and crystallization of the CsPbI₃ film by exploiting the atomic interaction between the ammonium group and the Pb–I framework. The grain boundaries and interfacial contact of the CsPbI₃ film have been improved, which leads to significant suppression in the non-radiative recombination and an enhancement in the charge transport ability. With these benefits, a high efficiency of 18.7% together with an extraordinarily high fill factor of 0.83–0.84 has been achieved, comparable to the highest records reported so far. Moreover, the cell exhibits ultra-high photoelectrical stability under continuous light illumination and high bias voltage with 96% of its initial power-conversion efficiency being sustained after 2000 h operation, even superior to the world-champion CsPbI₃ solar cell. The findings are promising for the development and application of all-inorganic PSCs using a simple inorganic additive strategy.     

In Situ Polymerizing Internal Encapsulation Strategy Enables Stable Perovskite Solar Cells toward Lead Leakage Suppression

Despite the outstanding power conversion efficiency (PCE) of perovskite solar cells (PSCs) achieved over the years, unsatisfactory stability and lead toxicity remain obstacles that limit their competitiveness and large-scale practical deployment. In this study, in situ polymerizing internal encapsulation (IPIE) is developed as a holistic approach to overcome these challenges. The uniform polymer internal package layer constructed by thermally triggered cross-linkable monomers not only solidifies the ionic perovskite crystalline by strong electron-withdrawing/donating chemical sites, but also acts as a water penetration and ion migration barrier to prolong shelf life under harsh environments. The optimized MAPbI₃ and FAPbI₃ devices with IPIE treatment yield impressive efficiencies of 22.29% and 24.12%, respectively, accompanied by remarkably enhanced environmental and mechanical stabilities. In addition, toxic water-soluble lead leakage is minimized by the synergetic effect of the physical encapsulation wall and chemical chelation conferred by the IPIE. Hence, this strategy provides a feasible route for preparing efficient, stable, and eco-friendly PSCs.     

Multi-Site Intermolecular Interaction for In Situ Formation of Vertically Orientated 2D Passivation Layer in Highly Efficient Perovskite Solar Cells

Surface passivation via 2D perovskite is critical for perovskite solar cells (PSCs) to achieve remarkable performances, in which the applied spacer cations play an important role on structural templating. However, the random orientation of 2D perovskite always hinder the carrier transport. Herein, multiple nitrogen sites containing organic spacer molecule (1H-Pyrazole-1-carboxamidine hydrochloride, PAH) is introduced to form 2D passivation layer on the surface of formamidinium based (FAPbI₃) perovskite. Deriving from the interactions between PAH and PbI₂, the defects of FAPbI₃ perovskite are effectively passivated. Interestingly, due to the multiple-site interactions, the 2D nanosheets are found to grow perpendicularly to the substrate for promotion of charge transfer. Therefore, an impressive power conversion efficiency of 24.6% and outstanding long-term stability are achieved for the 2D/3D perovskite devices. The findings further provide a perspective in structure design of novel organic halide salts for the fabrication of efficient and stable PSCs.