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High absorption ability and direct bandgap makes lead-based perovskite to acquire high photovoltaic performance. However, lead content in perovskite becomes a double-blade for counterbalancing photovoltaic performance and sustainability. Herein, we develop a methylammonium bismuth iodide (MBI), a perovskite-derivative, to serve as a lead-free light absorber layer. Owing to the short carrier diffusion length of MBI, its film quality is a predominant factor to photovoltaic performance. Several candidates of non-polar solvent are discussed in aspect of their dipole moment and boiling point to reveal the effects of anti-solvent assisted crystallization. Through anti-solvent engineering of toluene, the morphology, crystallinity, and element distribution of MBI films are improved compared with those without toluene treatment. The improved morphology and crystallinity of MBI films promote photovoltaic performance over 3.2 times compared with the one without toluene treatment. The photovoltaic device can achieve 0.26% with minor hysteresis effect, whose hysteresis index reduces from 0.374 to 0.169. This study guides a feasible path for developing MBI photovoltaics. [ABSTRACT FROM AUTHOR]

The existence of toxic Pb in perovskite solar cells may hinder the pace of commercialization. Based on the previous work, Ba2+ is most suitable for partially replacing Pb2+ among alkaline‐earth metal cations. However, a high substitution ratio may lead to poor film coverage. A detailed study of the effects on film formation with phenethylammonium chloride (PEACl) additive for large n (n > 40) quasi‐2D/3D mixed‐cation Pb–Ba perovskite (i.e. PEAxMA0.4−xFA0.6Pb0.9Ba0.1IyCl3−y) is presented. The perovskite layer with defects passivation exhibits efficient charge‐carrier transport, suppression of trap‐assisted recombination, and improved electron extraction capability. The mapping distribution of surface potentials is quantified by photo‐assisted Kelvin probe force microscopy to verify the carrier generation. Consequently, the power conversion efficiency (PCE) of the PEAxMA0.4−xFA0.6Pb0.9Ba0.1IyCl3−y perovskite solar cell is enhanced significantly from an averaged PCE of 15.0% of the pristine active layer to 18.1% and the champion PCE can achieve 19.1%. The corresponding device shows outstanding long‐term stability in air, retaining 90% of its initial PCE for more than 700 h. Herein, a promising strategy to passivate defects and improve the perovskite film quality for superior optoelectronic properties is provided. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskite solar cell (PSC) demonstrates outstanding photovoltaic characteristics. However, the instability under high temperature and high relative humidity remains an obstacle that needs to be overcome. Furthermore, the rapid growth of perovskite crystals causes a lot of defect formation in the perovskite active layer, leading to insufficient stability. Two‐dimensional g–C3N4 is a typical lewis base, providing electron pairs for bonding and is suitable as a template for controlling the nucleation of the perovskite active layer. Herein, tunable g–C3N4 by calcining the precursors (cyanamide, dicyandiamide, and urea) at different conditions to control the grain size and to passivate perovskite crystal is constructed. The Kelvin probe force microscopy study reveals that the successful defect passivation by urea‐polymerized g–C3N4 (UCN) at grain boundaries could induce the suppression of non‐radiative recombination. Adding the least polymerized UCN into a perovskite film allows for uniform surface morphology and a reduced trap density. UCN coordinated with the perovskite provides an efficient path for electron injection to the electron transport layer. The unencapsulated PSCs with UCN additive achieve a maximum power conversion efficiency of 20.03% and retain ≈93% of their initial efficiency values after aging for 960 h at 25 °C and relative humidity of 30%. [ABSTRACT FROM AUTHOR]

Ion migration in organometal halide perovskite solar cell (OHPSC) and crystal structure evolution of organometal halide perovskites (OHPVSKs) in air are considered as one of the critical factors for unstable performance and of the urgent issues for the reliability of OHPSCs. Herein, a novel cation of acetamidinium (Aa+) with stronger coordinated bond with I− than methylammonium is induced into OHPVSK to stabilize its crystal structure. By incorporating Aa+ ions into OHPVSKs, the power conversion efficiency (PCE) of OHPSC without an encapsulation can maintain higher than 75% of its initial PCE after a 200 h humidity (60–80% relative humidity (RH) in air) or a 24 h thermal stress test (85 °C in dry N2). The Aa–MAPbI3 device exhibits an outstanding efficiency of 20.68%, and over 80% of initial PCE is maintained after a 1300 h damp heat as encapsulated. This novel cation can be easily incorporated into OHPVSK via a hot casting process in air with a high environmental tolerance as compared with that from the conventional coating process, which suffers from sophisticated crystallization steps and a strict processing atmosphere. It extends processing windows for OHPVSK fabrication and provides a promising path toward mass production and further commercialization. [ABSTRACT FROM AUTHOR]

In present work, we focused on the improvement of short-circuit current density (J sc ) by using zinc-doped TiO 2 (Zn-doped TiO 2 ) as electron transport layer. Various Zn-doped TiO 2 compact layers with different doping concentrations are prepared by sol-gel method followed thermal treatment, and they were then used to fabricate perovskite solar cell. Effects of zinc (Zn) on the power conversion efficiency (PCE), absorption behavior, crystal structure, electrical conductivity, and surface morphology are systemically elucidated. Charge carrier dynamics between perovskite active layer and titanium dioxide (TiO 2 ) compact layer is discussed too. When the dopant concentration is less than 5.0 mol%, the absorption behavior, electrical conductivity and charge separation efficiency increase with Zn doping concentration. In contrast, when the Zn dopant is 7.0 mol%, it results in the decay of these properties mentioned. According to the optimized processing of perovskite solar cells, the J sc is increased from 18.5 to 22.3 mA/cm 2 so as to the PCE is significantly improved from 11.3% to 14.0%. [ABSTRACT FROM AUTHOR]

• The SPS treatment renders chloride gradient in NiO x of hole transport layer to exhibit graded energy level. • The graded energy level of NiO x in inverted OHPSCs shows recorded V oc for both wide and narrow E g. • PCE of OHPSC with the SPS treated NiO x achieves 19.53% with a record V oc of 1.16 V in NiO x based inverted OHPSCs. • The encapsulated devices can maintain 80% of initial PCE after 1500 h damp heat tests (85 °C and 85 RH%). A carrier transport layer and its interfacial effects on an organometal halide perovskite light harvesting layer play an influential factor in either photovoltaic performance or long-term stability of a perovskite solar cell (OHPSC). Although the understandings of the carrier transport layers and interfacial effects on regular structured OHPSCs have been explored, knowledge of an interface between hole transport layer of NiO x and perovskite in an inverted OHPSC is still necessary to be developed. Here, we performed a universal NiO x film with the sequential passivation strategy of NiCl 2 (SPS-NiCl 2 treatment) for either wide bandgap or narrow bandgap of OHPSCs. The SPS-NiCl 2 treated NiO x film not only implements the passivation at the perovskite layer/NiO x film interface but also confers itself a gradient energy level of valance band inducing by chloride. Comprehensive characterizations reveal that the SPS-NiCl 2 treated NiO x film suppresses non-radiative recombination at the interface and enlarges the splitting of the quasi-Fermi level at the interfaces. The photoconversion efficiency (PCE) of the champion device comprised of the SPS-NiCl 2 treated NiO x film can achieve 19.53% with a record V oc of 1.16 V, the lowest V oc deficit of 390 mV in NiO x based inverted OHPSCs. The corresponding devices with encapsulation also exhibit superior long-term stability, and over 80% of initial PCE can be maintained after 1500 h damp-heat test. This study sheds the light on managing the interfacial issues of an inverted OHPSC and offers a feasible path to develop a universal hole transport layer for perovskite layers with different energy bandgap. [ABSTRACT FROM AUTHOR]

• Photovoltaics of the lead-free absorber layer, Ag 3 BiI 6 , were obtained from the thermal-assisted blade-coating technique. • Modification of carrier transporting layers renders Ag 3 BiI 6 to exhibit superior photovoltaic performance with 2.77%. • The champion device with a one-millimeter square active area can achieve 2.03%. • The devices can maintain 80% of initial PCE after 3,000 h stability tests in ambient without encapsulation. Nowadays, high-efficiency perovskite solar cells mainly comprise a lead-based light-absorber layer. Without a doubt, the unprecedented power conversion efficiency (PCE) of perovskite solar cells makes them an optimistic solution for sustainable or renewable energy sources. However, the toxic composition of lead, a notorious element for organisms, in perovskite solar cells and its stability in an ambient environment raise public concern. Therefore, resolving these two issues is urgent for developing perovskite solar cells. In this study, Ag 3 BiI 6 rudorffite was selected as an active layer prepared by the thermal-assisted doctor blade coating method to replace the conventional lead-based perovskite active layer. To align the energy level between carrier transporting layers and the Ag 3 BiI 6 light absorber layer, doping both carrier transporting layers improved the PCE of doctor-bladed devices from 2.06% to 2.77%. These devices can maintain 90% of their initial PCE after storing them unencapsulated in an ambient environment for over 3,000 h. This study also demonstrates a large 1.00 cm2 device with a PCE of 2.03%. The lead-free, air-stable, and mass production processible properties make it a promising selection for photovoltaic materials. [ABSTRACT FROM AUTHOR]

Bulk heterojunction (BHJ) photovoltaics represent one of the most promising technologies in low-cost, high-throughput, environmentally friendly energy conversion. Morphological control is one pillar of the recent remarkable progress in power conversion efficiency. This review focuses on morphological control by processing with solvent additives, which has been extensively adopted and exhibits promising compatibility with large-scale processing. Recent investigations including material selection, morphological variations at various length scales, and interpretations of the interaction among additives and BHJ materials will be discussed. Insights into the role of solvent additives represent an important resource for further improvement in materials and processing designs. [ABSTRACT FROM AUTHOR]