Perovskite solar cells (PSCs) have the potential to produce solar energy at a low cost, with flexibility, and high power conversion efficiency (PCE). However, there are still challenges to be addressed before mass production of PSCs, such as prevention from degradation under external stresses and the uniform, large-area formation of all layers. Among them, the most challenging aspect of mass production of PSCs is creating a high-quality perovskite layer using environmentally sustainable processes that are compatible with industry standards. In this review, we briefly introduce the recent progresses upon eco-friendly perovskite solutions/antisolvents and film formation processes. The eco-friendly production methods are categorized into two: (1) employing environmentally friendly solvents for perovskite precursor ink/solution, and (2) replacing harmful, volatile antisolvents or even limiting their use during the perovskite film formation process. General considerations and criteria for each category are provided, and detailed examples are presented, specifically focused on the works have done since 2021. In addition, the importance of controlling the crystallization behavior of the perovskite layer is highlighted to develop antisolvent-free perovskite formation methods.

In state-of-the-art n-i-p structured perovskite solar cells (PSCs), a dopant for doping hole transporting materials (HTMs) is a crucial component, which affects not only the electrical properties of HTMs, but also the performances and stabilities of PSCs. In this paper, we report new dual functional ionic liquids (ILs) consisting of various alkylammoniums (from butyl to decyl) and bis(trifluoromethylsulfonyl)imide (denoted as BATFSI, HATFSI, OATFSI, and DATFSI) as a dopant and surface passivator for highly efficient and stable PSCs and modules. Among these ILs, OATFSI provides enough miscibility with a poly(triarylamine) solution, which results in a smoother morphology of the hole transporting layer (HTL) with an enhanced electrical property via efficient doping. Simultaneously, OATFSI passivates the perovskite surface in situ, during spin-coating deposition of the HTL. Highly efficient and stable OATFSI-based PSCs are fabricated with a mesoporous n-i-p structure and a maximum power conversion efficiency (PCE) of 23.34%, due to reduced non-radiative recombination and better charge extraction. To verify the scalability of our new IL dopants, perovskite modules with a high PCE of 18.54% (on the aperture area of 224.89 cm(2)) and 19.91% (on the active area of 209.39 cm(2)) are demon...

Current density plays a substantial role in monolithic tandem solar cells; however, it is difficult to control because subcells and auxiliary layers are stacked and serially connected vertically to obtain higher voltages. The vertically stacked structure intrinsically triggers inevitable parasitic absorption. In current typical perovskite/silicon two-terminal (2-T) tandem solar cells, 5–10 layers are placed on the light path, even though they are not current generating layers. These layers usually include transparent window layers, buffer layers, carrier extraction layers, and recombination layers. Therefore, the development of top contact-free architectures to reduce parasitic absorption in 2-T tandem solar cells is required for achieving high efficiency. In this study, a top contact-free perovskite/silicon 2-T tandem solar cell with quasi-interdigitated intermediate electrodes (Q-IDIEs) is reported for the first time. Several layers placed above the perovskite layer in conventional devices are relocated to the backside of the perovskite. The Q-IDIE, composed of a patterned Ni/NiOX shell above the full-deposited TiO2, was fabricated by the following processes: photolithography, lift-off, and oxidation. The device results in 4.23% efficiency with an open-circuit voltage of 1.54 V. This tandem architecture is expected to be a breakthrough for overcoming the theoretical efficiency limit of single-junction solar cells with further optimization.

Perovskite solar cells (PSCs) have emerged as the next generation of solar cells because of the promising nature of creating tandem solar cells with Si photovoltaics. Wide-bandgap PSCs are developed to improve the power conversion efficiency (PCE) and stability of tandem devices. For the mass production of tandem solar cells, not only is a limitation of scalable coating a critical factor, but uncontrollable grain growth in ambient air impedes commercialization. Serious differences in morphology depending on the experimental environment are found. In the ambient air processing system, severe wrinkles and voids resulting in deteriorated photovoltaic performance are found as compared with those in N2 condition. It is suggested that humidity in the air plays a crucial role in the remaining perovskite intermediate phase and the rate of solvent evaporation during the spin-coating procedure. Herein, void- and wrinkle-free perovskite films using methyl ammonium chloride and formamide are fabricated, thus leading to efficient PSCs with a PCE of 20.6%. Furthermore, newly designed perovskite films to blade coating for large-area fabrication as well as to semitransparent PSCs for a four-terminal silicon/perovskite tandem solar cell with a PCE of 25.2% are applied.

　Interface modification of perovskite solar cells (PSCs) has been widely explored not only to achieve defect passivation but also to facilitate charge transport and stabilize the physical/electrical contact at device interfaces. In this study, [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (CEPA) is introduced as an interface modifier at the interface of perovskite and the hole transporting material (HTM) layer into n-i-p PSCs. CEPA reduces surface traps, manipulates the surface dipole for energy-level alignment, and induces molecular interaction at the interface of the CEPA-HTM for enhanced interfacial adhesion energy and good mechanical stability. The power conversion efficiency of interface-optimized PSC is 23.6% using a 2D/3D perovskite structure, representing the highest efficiency among poly(triarylamine) HTM-based devices. The encapsulated CEPA-treated PSCs maintain nearly 90% of their initial efficiency during a damp heat lasting for more than 1530 h and retain their initial efficiency during continuous operation under illumination.

　Since the first publication by Miyasaka in 2009 on the use of lead halide perovskite as a light-harvesting material (Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc.2009, 131, 6050), unprecedented successes have been achieved and great efforts have been made in the field of perovskite solar cells (PSCs) to push the power conversion efficiency (PCE) past 25%, which corresponds to ∼80% of this material’s theoretical bandgap limit determined on the basis of the Shockley–Queisser theory. Recent progress is mainly attributed to the development of key strategies that effectively reduce the defects on the surface of the perovskite layer and minimize non-radiative recombination at the interfaces, thereby enhancing device efficiency. For future development of PSCs with PCEs exceeding 26%, this Perspective highlights an investigation of the key factors that have allowed realization of efficient PSCs with state-of-the-art PCEs and includes a discussion of practical strategies, including full optimization of the electron-transport layer, minimization of defect loss related to non-radiative recombination, and enhancement of light-harvesting near the band-edge.

　The photovoltaic performance and scalability potential of a semitransparent perovskite solar cells (ST-PSCs) are primarily determined by the optoelectronic properties of the top transparent conducting electrode (TCE) used. Herein, we demonstrate the scalable fabrication of ST-PSC using a three-dimensional (3D) TCE consisting of (i) a sputtered amorphous indium-tin-oxide (a-ITO) film and (ii) silver (Ag) mesh subelectrodes prepared via a 3D direct-ink writing technique. At an optimized aspect ratio of 0.5, the a-ITO/Ag mesh 3D TCE exhibits a sheet resistance of < 1 Ω/□ and a transparency of ~85%. Utilizing the a-ITO/Ag mesh as a top contact, standard (0.07 cm2) and large-area (1.0 cm2) ST-PSCs achieved power conversion efficiencies (PCE) of 16.26% and 15.52%, respectively, with > 85% transmittance in the near-infrared region. Moreover, the ST-PSCs displayed superior ambient and thermal stability than the opaque PSCs due to the presence of a-ITO buffer that prevents moisture ingress and ions migration. Using ST-PSC as a top cell, the standard (0.07 cm2) and large-area (1.0 cm2) four-terminal ST-PSC/SiSC tandem cells achieved PCEs of 26.47% and 24.70%, respectively. To the best of our knowledge, our tandem cell showed the minimum efficiency roll-off among all the reported large-area tandem cells, manifesting the scalability potential of our ST-PSCs.

　To approach the theoretical efficiency of perovskite solar cells (PSCs), the defects in perovskites should be managed. Among different types of defects, halide vacancies easily form on the surface of perovskite grains (PGs), hindering perovskite stability and the charge-transport process by trapping charge carriers. In this work, oxidized black phosphorus quantum dots (O-BPQDs) are incorporated into a perovskite to resolve these issues. Oxygen atoms of the O-BPQDs interact with uncoordinated Pb (halide vacancies), forming grain interconnections. These interactions reduce halide vacancies and suppress the overall recombination kinetics. Along with defect reduction, the O-BPQDs offer an efficient charge-transport channel across individual PGs. We achieve a best power-conversion efficiency (PCE) of 22.34% for SnO2-based PSCs and of 23.1% for TiO2-based PSCs. These PSCs exhibit moisture stability in a relative humidity (RH) 40% environment comparable to 3D/2D perovskites. Our strategy provides practical applicability and versatility for PSCs to approach the theoretical PCE value.

　Perovskite solar cells (PSCs) are emerging next-generation photovoltaics, and some breakthroughs for the commercialization have been rapidly made. To develop the technologies for large-area modules, economically feasible fabrication using a roll-to-roll (R2R) solution process may be the ultimate target for the fabrication of PSCs. In order to achieve successful R2R production of PSCs, however, several issues still need to be addressed. Roll-based continuous and scalable deposition of perovskite and charge transporting layers on a flexible substrate needs to be developed to obtain high-quality R2R-processed PSCs. There are also critical factors involved in accomplishing R2R fabrication: heat treatment at low temperature and a short processing time over the whole process with industrial-compatible methods. We briefly discuss this perspective: scalable deposition of layers, considerations for the R2R process, and progress and challenges in the R2R fabrication of the PSCs.

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　This report addresses indium oxide doped with titanium and tantulum with high near-infrared transparency to potentially replace the conventional indium tin oxide transparent electrode used in semitransparent perovskite devices and top cells of tandem devices. The high near-infrared transparency of this electrode is possibly explained by the lower carrier concentration, suggesting less defect sites that may sacrifice its optical transparency. Incorporating this transparent electrode into semitransparent perovskite solar cells for both the top and bottom electrodes improved the device performance through possible reduction of interfacial defect sites and modification in energy alignment. With this indium oxide-based semitransparent perovskite top cell, we also demonstrated four-terminal perovskite–silicon tandem configurations with improved photocurrent response in the bottom silicon cell.

　Perovskite solar cells in an n-i-p structure record high power conversion efficiency, but issues of insufficient thermal stability and the high cost of p-type hole transporting materials have been raised as drawbacks. H2-phthalocyanine (Pc) is introduced as a hole transport material to ensure the thermal stability and simultaneously have served surface passivation effects on hybrid halide perovskites as a Lewis base. Pyrrolic nitrogen in the Pc reacts with uncoordinated Pb2+ ions on the perovskite surface. Upon enhancing the interfacial interaction between phthalocyanine and the perovskite, the open circuit voltage in devices increases as compared to that of devices using a metal-phthalocyanine complex. While the phthalocyanine-applied device maintains superior thermal long-term stability, the power conversion efficiency also exceeds 20%.