Methylammonium Bromide Assisted Crystallization for Enhanced Lead‐Free Double Perovskite Photovoltaic Performance

Abstract

Cs2AgBiBr6, has recently gained wide attention as a possible alternative to lead‐halide perovskites, considering the nontoxicity and improved stability. However, this double perovskite suffers from defects, especially deep electron traps, severely hampering the photovoltaic performance. This work reports a simple method to control the double perovskite crystallization by adding volatile salts into the precursor solution. X‐ray diffraction patterns reveal that the organic cation with suitable radius (such as methylammonium, MA+) is introduced into the perovskite lattice, forming an organic/inorganic mixed double perovskite intermediate phase. The organic salt is thereafter fully evaporated during high temperature annealing, and the all‐inorganic double perovskite is obtained with dense surface and less pin‐holes. From optical and electrical characterization, it is concluded that the Cs2AgBiBr6 film exhibits high quality, with higher light absorptance and emission. Reduced trap density and longer carrier lifetime are also observed. The improved Cs2AgBiBr6 film is beneficial for efficient carrier collection with suppressed defect‐assisted recombination. With this strategy, a power conversion efficiency (PCE) of 2.53% is achieved for the champion Cs2AgBiBr6‐based solar cell device, which is significantly higher compared to the control device with 1.43% PCE. This work is therefore helpful for further improvement of inorganic lead‐free perovskite materials for optoelectronic applications.

Recent progress of lead-free bismuth-based perovskite materials for solar cell applications

“…One example is the addition of MABr into a Cs 2 AgBiBr 6 precursor, which greatly suppressed defect formation in the film, promoting more efficient electron transfer and contributing to a higher photocurrent. 113 Besides, the use of PIF8-TAA with a deeper HOMO energy level as the hole transport layer can reduce the energy transfer at the interface and improve the interfacial charge transfer efficiency, which eventually leads to the increase of V oc . 47…”

Recent Progress in Cesium‐Based Lead‐Free Halide Double Perovskite Materials for Photovoltaic Applications

“…The modified PSCs have shown the champion PCE of 2.53%, which was significantly higher than the PCE (1.43%) of the control device. [ 134 ] Besides, Yang et al suppressed the charge carrier recombination using an additive engineering approach. The film quality of the absorber is improved with the addition of guanidinium thiocyanate (GuaSCN), and the device exhibited a superior PCE of 3.02%.…”

Novel Ag-based thin film solar cells: concept, materials, and challenges

“…9(a), Xiu et al 82 used the capillary assisted method to successfully prepare uniform Cs 2 AgBiBr 6 thin films at a large-scale. The annealing of pre-formed films in DMSO steam to assist the grain growth of the Cs 2 AgBiBr 6 absorber was first proposed by Shadabroo et al 83 Absorber crystallization can be promoted by adding volatile methyl ammonium bromide (MABr) 84 to the Cs 2 Ag-BiBr 6 precursor solution. As a result of the optimization, the defect density was reduced, the carrier lifetime was prolonged, and the electron extraction efficiency of the electron transport material became higher.…”