Long Electron–Hole Diffusion Length in High‐Quality Lead‐Free Double Perovskite Films

Abstract

Developing environmentally friendly perovskites has become important in solving the toxicity issue of lead-based perovskite solar cells. Here, the first double perovskite (Cs AgBiBr ) solar cells using the planar structure are demonstrated. The prepared Cs AgBiBr films are composed of high-crystal-quality grains with diameters equal to the film thickness, thus minimizing the grain boundary length and the carrier recombination. These high-quality double perovskite films show long electron-hole diffusion lengths greater than 100 nm, enabling the fabrication of planar structure double perovskite solar cells. The resulting solar cells based on planar TiO exhibit an average power conversion efficiency over 1%. This work represents an important step forward toward the realization of environmentally friendly solar cells and also has important implications for the applications of double perovskites in other optoelectronic devices.

From Lead Halide Perovskites to Lead‐Free Metal Halide Perovskites and Perovskite Derivatives

“…[55] Second, for B(III) cations, the transition metal cations with multiple oxidation states and/or partially occupied d or f orbitals are not desirable for designing photovoltaic absorbers, because they may introduce deep defect states and too localized band edges. Largesize single crystals, [155,[172][173][174] nanocrystals, [175][176][177][178] and highquality films [179][180][181][182] The element Au is half-colored because it exists only in the compounds A 2 Au 2 X 6 with A = Rb, Cs and X = Cl, Br, I. Most of the reported double perovskites are fluorides and chlorides, [158,159] which generally have too large bandgaps for photovoltaic applications.…”

“…The indirect bandgap is explained by the mismatch in angular momentum of the atomic orbitals of Ag and Bi that comprise the valence band top and the conduction band bottom. [179][180][181] Greul et al [179] first demonstrated the synthesis of Cs 2 Ag-BiBr 6 films and then used the films to fabricate solar cells in the regular mesoporous structure. Defect calculations showed that Bi vacancy and Ag-on-Bi antisite create deep states in the bandgap and thus should be carefully suppressed during the synthesis process for optimized optoelectronic properties.…”

“…Defect calculations showed that Bi vacancy and Ag-on-Bi antisite create deep states in the bandgap and thus should be carefully suppressed during the synthesis process for optimized optoelectronic properties. Recently, Ning et al [180] reported the first Cs 2 AgBiBr 6 -based solar cells using the planar structure, which exhibited an average PCE of over 1%. There have been a few reports on Cs 2 AgBiBr 6 -based solar cells.…”

Progress of Lead‐Free Halide Double Perovskites

“…[119] However, the experimental results demonstrated that a lot of work was still to be done to ensure the reliability of this method. [78,79,118] The solution is then cooled to room temperature and deposited onto a charge-transport layer such as TiO 2 and SnO 2 by spin-coating. [120] Apart from the report by Greul et al in which Cs 2 AgBiBr 6 precursor was directly dissolved in dimethyl sulfoxide (DMSO) prior to device fabrication, [80] halide double perovskites of Cs 2 AgBiBr 6 are commonly prepared by an initial synthesis of corresponding single crystals, which are subsequently redissolved in organic solvents such as DMSO and dimethyl formamide (DMF) at elevated temperatures.…”

“…A colorless solid, chloride double perovskite, Cs 2 NaBiCl 6 , has also been prepared. [78][79][80] This research area has blossomed owing to the numerous efforts made already to solve the issues of toxicity and stability in perovskite solar cells. [76,77] Notably, study interest has been moved to halide based double perovskites for potential PV application.…”