Intermediate Phase‐Free Process for Methylammonium Lead Iodide Thin Film for High‐Efficiency Perovskite Solar Cells

Abstract

Solvent engineering by Lewis‐base solvent and anti‐solvent is well known for forming uniform and stable perovskite thin films. The perovskite phase crystallizes from an intermediate Lewis‐adduct upon annealing‐induced crystallization. Herein, it is explored the effects of trimethyl phosphate (TMP), as a novel aprotic Lewis‐base solvent with a low donor number for the perovskite film formation and photovoltaic characteristics of perovskite solar cells (PSCs). As compared to dimethylsulfoxide (DMSO) or dimethylformamide (DMF), the usage of TMP directly crystallizes the perovskite phase, i.e., reduces the intermediate phase to a negligible degree, right after the spin‐coating, owing to the high miscibility of TMP with the anti‐solvent and weak bonding in the Lewis adduct. Interestingly, the PSCs based on methylammonium lead iodide (MAPbI3) derived from TMP/DMF‐mixed solvent exhibit a higher average power conversion efficiency of 19.68% (the best: 20.02%) with a smaller hysteresis in the current‐voltage curve, compared to the PSCs that are fabricated using DMSO/DMF‐mixed (19.14%) or DMF‐only (18.55%) solvents. The superior photovoltaic properties are attributed to the lower defect density of the TMP/DMF‐derived perovskite film. The results indicate that a high‐performance PSC can be achieved by combining a weak Lewis base with a well‐established solvent engineering process.

Selection of a Suitable Solvent Additive for 2-Methoxyethanol-Based Antisolvent-Free Perovskite Film Fabrication

“…To investigate the cause of the insufficient coverage following NMP application, we analyzed the as-deposited films. As shown in the photographs of the real films, the transparency of the as-deposited films due to the characteristics of the MAI-PbI 2 -NMP phase 13,33 increased with an increasing amount of NMP, suggesting that the intermediate phase became dominant (Figure S10). Similarly, as the concentration of NMP increased, the MAPbI 3 (110) peak intensity decreased in the XRD patterns while, simultaneously, the intermediate phase peak intensity increased at 8.2°.…”

“…Recently, similar to the adoption of 2MOE as a solvent based on the D N , − several studies have been conducted to apply solvents or additives based on the D N . , In this study, we compared various solvents with different D N as additives in the 2MOE-based antisolvent-free process to identify alternatives to the precipitation-causing DMSO. Through this, we discovered that the lower the D N value of the additive, the lower the precipitation level in the precursor solution.…”

Resolving Mixed Intermediate Phases in Methylammonium-Free Sn–Pb Alloyed Perovskites for High-Performance Solar Cells

“…Ding et al adopted N -methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc) as co-solvents to decrease the transition window of intermediate phase [ 39 ]. Furthermore, Lee et al used trimethyl phosphate (TMP), having a low donor number, as a replacement to DMSO, thereby realizing an intermediate phase–free process for preparing high-performance PSC [ 40 ]. Therefore, accelerating the transition from the intermediate phase into the perovskite phase or directly forming the perovskite phase without inducing an intermediate phase can be a potential solution to eliminate the negative effect of mixed intermediate phases in MA-free Sn–Pb alloyed perovskites.…”

Enhanced Structural Stability and Pressure‐Induced Photoconductivity in Two‐Dimensional Hybrid Perovskite (C6H5CH2NH3)2CuBr4

“…Owing to the remarkable combination of superior mobility, high light absorption coefficient and long carrier diffusion length, perovskite-like materials are attracting interest both in terms of fundamental material science and potential applications in the nextgeneration photovoltaic field. [1,2] To date, the low structural stability (hydrolysis and oxidation in air) and the existence of toxic elements (Pb, Cd, Hg etc.) in current commercial production of perovskite solar cells have severely limited their practical applicable scope as optoelectronic devices.…”