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Metal halide perovskite solar cells (PSCs) have witnessed a swift increase in power conversion efficiency in the past decade, emerging as one of the most promising next-generation photovoltaic technologies for commercialization and low-carbon energy generation. Through significant efforts in optimizing the processing techniques, high-quality perovskite thin films can now be prepared with polycrystalline morphologies consisting of monolayer grains. Nevertheless, defects and microstructural disorders still form at the surface/heterointerface and in the bulk of the films. Post-treatment of the as-crystallized films has been intensively investigated for passivating these defects, being proved effective for improving the device performance. In this review, the versatile strategies for post-treating the surface of perovskite thin films toward morphology control, defect passivation, and band alignment are discussed. The tailored surface properties are correlated to charge dynamics at interfaces and photovoltaic performance of PSCs. Since the perovskite heterostructures prepared by simple post-treatments may suffer from degradation at high temperatures, the recent advances in preparing phase-pure and stable perovskite heterostructures are also discussed. Finally, a perspective elaborating future opportunities for further enhancing the efficiency and stability of PSCs is provided. © 2023 Wiley-VCH GmbH.

All-inorganic perovskites are promising for solar cells owing to their potentially superior tolerance to environmental factors, as compared with their hybrid organic-inorganic counterparts. Over the past few years, all-inorganic perovskite solar cells (PSCs) have seen a dramatic improvement in certified power conversion efficiencies (PCEs), demonstrating their great potential for practical applications. Pb, Sn, and Ge are the most studied group IVA elements for perovskites. These group IVA cations share the same number of valence electrons and similarly exhibit the beneficial antibonding properties of lone-pair electrons when incorporated in the perovskite structure. Meanwhile, mixing these cations in all-inorganic perovskites provides opportunities for stabilizing the photoactive phase and tailoring the bandgap structure. In this mini-review, we analyze the structural and bandgap design principles for all-inorganic perovskites featuring mixed group IVA cations, discuss the updated progress in the corresponding PSCs, and finally provide perspectives on future research efforts faciliating the continued development of high-performance Pb-less and Pb-free all-inorganic PSCs. © 2023 The Royal Society of Chemistry.

The remarkable ramping of record power conversion efficiencies in perovskite solar cells (PSCs) has stimulated the growth of this technology towards commercialization. However, there remain challenges and opportunities for further improving their efficiency and stability. Featuring the variety of functional group in the constituting ions, ionic liquids (ILs) exhibit versatile properties and functions that can be leveraged to the development of improved PSCs. Herein with a systematic review on the recent progress in the application of ILs to PSCs, we show that based on the different roles of ILs in the film and device settings, IL can facilitate the thin-film synthesis of perovskites, improve the properties of charge-transport layers, and ameliorate the interfacial energetics at device interfaces. In particular, the ILs-perovskite interactions of two different types (Lewis acid-base interaction and hydrogen bonding) are the essential chemistries underpinning observed efficiency and stability improvements in PSCs, which represent a vast research paradigm in the field of energy chemistry. © 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences

State-of-the-art perovskite solar cells (PSCs) have bandgaps that are invariably larger than 1.45 eV, which limits their theoretically attainable power conversion efficiency. The emergent mixed-(Pb, Sn) perovskites with bandgaps of 1.2–1.3 eV are ideal for single-junction solar cells according to the Shockley–Queisser limit, and they have the potential to deliver higher efficiency. Nevertheless, the high chemical activity of Sn(II) in these perovskites makes it extremely challenging to control their physical properties and chemical stability, thereby leading to PSCs with relatively low PCE and stability. In this work, the authors employ the Lewis-adduct SnF2·3FACl additive in the solution-processing of ideal-bandgap halide perovskites (IBHPs), and prepare uniform large-grain perovskite thin films containing continuously functionalized grain boundaries with the stable SnF2 phase. Such Sn(II)-rich grain-boundary networks significantly enhance the physical properties and chemical stability of the IBHP thin films. Based on this approach, PSCs with an ideal bandgap of 1.3 eV are fabricated with a promising efficiency of 15.8%, as well as enhanced stability. The concept of Lewis-adduct-mediated grain-boundary functionalization in IBHPs presented here points to a new chemical route for approaching the Shockley–Queisser limit in future stable PSCs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We demonstrate the feasibility of a nonsalt-based precursor pair - inorganic HPbI3 solid and organic CH3NH2 gas - for the deposition of uniform CH3NH3PbI3 perovskite thin films. The strong room-temperature solid-gas interaction between HPbI3 and CH3NH2 induces transformative evolution of ultrasmooth, full-coverage perovskite thin films at a rapid rate (in seconds) from nominally processed rough, partial-coverage HPbI3 thin films. The chemical origin of this behavior is elucidated via in situ experiments. Perovskite solar cells, fabricated using MAPbI3 thin films thus deposited, deliver power conversion efficiencies up to 18.2%, attesting to the high quality of the perovskite thin films deposited using this transformative process. © 2016 American Chemical Society.

Doping and/or alloying in the various layers in perovskite solar cells (PSCs) is playing a key role in the success of this new photovoltaic (PV) technology. Here we present a brief review of doping and alloying approaches used to enhance the efficacy of the hybrid organic-inorganic perovskite (HOIP) layer, the electron-transporting layer (ETL), the hole-transporting layer (HTL), and the electrode layers in PSCs. While the effectiveness of these approaches is beyond doubt, the fundamental understanding of doping and alloying in the majority of the cases is lacking. This presents vast research opportunities in elucidating the roles of doping and alloying, and the rational design and implementation of these approaches for enhanced PSCs performance. © The Royal Society of Chemistry.

We report herein the discovery of methylamine (CH3NH2) induced defect-healing (MIDH) of CH3NH3PbI3 perovskite thin films based on their ultrafast (seconds), reversible chemical reaction with CH3NH2 gas at room temperature. The key to this healing behavior is the formation and spreading of an intermediate CH3NH3PbI3.xCH3NH2 liquid phase during this unusual perovskite-gas interaction. We demonstrate the versatility and scalability of the MIDH process, and show dramatic enhancement in the performance of perovskite solar cells (PSCs) with MIDH. This study represents a new direction in the formation of defect-free films of hybrid perovskites. A perovskite smoothie: Treating CH3NH3PbI3 (MAPbI3) perovskite thin films with methylamine gas induces a rapid collapse of the perovskite structure and formation of a liquid phase. Removing the gas causes conversion back into the perovskite structure giving a smooth defect-free film. Using the film in perovskite solar cells enhances their performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Methylammonium lead trihalide perovskites are attracting intensive interest due to its high photovoltaic performance, low cost and one-step solution processability. Since the morphology of the perovskite thin films play the central role on the cell performance, a plethora of methods have been developed to fabricate uniform perovskite film. Herein, we demonstrate that an innovative approach by applying mixed lead salts (PbI2 + PbCl2) to facilitate reproducible fabrication of compact perovskite thin film. It is proposed that rapid reaction kinetics of PbI2 with MAI enables preformation of perovskite within the intermidiate film matrix, working as homogeneously located domains for squential growth of the PbCl2-derived perovskite. The as-prepared perovskite film exhibited a overall textured crystal morphology and superior compactness, which enables excellent light absorption and long-time preservation of photogenerated charge carriers and therefore exhibits 11% efficiency in planar-structured solar cells. The annealing testing shows the film also possesses very stable morphology upon long-time heating, indicative of the insensitivity of our new protocol to the preparation condition and also the promising thermal stability of its based solar cells. The simplicity of the one-step solution-processing and the high morphology stability of the as-prepared perovskite film endow this mixing lead salts method with feasibility of the large-scale fabrication. © 2014 American Chemical Society.