Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites

Abstract

Wide-bandgap (WBG) formamidinium-cesium (FA-Cs) lead iodide-bromide mixed perovskites are promising materials for front cells well-matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open-circuit voltage (V ) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA-Cs WBG perovskite with the aid of a formamide cosolvent, light-induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (E ≈ 1.75 eV) exhibit a high V of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm solar cells, the highest among the reported efficiencies for large-area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long-term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.

Two‐Terminal Perovskites Tandem Solar Cells: Recent Advances and Perspectives

“…However, high incorporation contents of Cs and Br salts as undesired nonperovskite phases could induce high density of deep traps, which caused long‐term phase instability, high V OC deficit, and hysteretic behavior. Kim et al demonstrated that control over the crystallization of FA/Cs perovskite films could efficiently suppress the light‐induced phase segregation and hysteresis problems. By introducing a highly polar additive formamide (CH 3 NO) into the precursor solution, the solubility of the Cs salt increased, which led to the less formation of yellow δ‐phases and reduced defects density in films.…”

Zwitterion Coordination Induced Highly Orientational Order of CH3NH3PbI3 Perovskite Film Delivers a High Open Circuit Voltage Exceeding 1.2 V

“…Organic–inorganic halide perovskite materials such as CH 3 NH 3 PbX 3 (MAPbX 3 , X = I, Br, and Cl) have many fascinating optoelectronic properties such as tunable bandgaps, long carrier diffusion lengths, large absorption coefficients, etc., enabling organic–inorganic hybrid perovskite solar cells (PSCs) as an emerging thin film solar cell technology with the certified power conversion efficiency (PCE) reaching 23.7%, achieved by optimizing the device structure and engineering the perovskite/electrode interfaces as well as the perovskite layer . Noteworthily, the commonly used MAPbI 3 light‐absorbing layer, solution‐processed MAPbI 3 perovskite film usually suffers from random crystalline grain orientation and high trap density, resulting in inferior PCE with open circuit voltage ( V oc ) being typically below 1.2 V . Over the past few years, continuous efforts have been devoted to optimize the composition, phase, and quality of the MAPbI 3 perovskite layer .…”

Double‐Side‐Passivated Perovskite Solar Cells with Ultra‐low Potential Loss

“…In polycrystalline materials, especially for solution‐processed perovskites, it has been increasingly recognized that defects are mainly located at front‐side, rear‐side surfaces, and grain boundaries . Therefore, further advances in perovskite solar cells will depend upon how to suppress defect density in perovskite semiconductors . It is well known that the grain interior has single crystal‐like quality, which usually does not count for defects rich region .…”