Co-evaporation as an optimal technique towards compact methylammonium bismuth iodide layers

TL;DR

This study demonstrates that thermal co-evaporation of MAI and BiI3 produces uniform, compact methylammonium bismuth iodide layers, advancing lead-free perovskite solar cell fabrication.

Contribution

First investigation of MBI thin films prepared via co-evaporation, showing improved morphology and surface coverage over solution methods.

Findings

Co-evaporated MBI layers are uniform and compact.

Pure MBI composition yields better film quality.

Broadens deposition options for lead-free perovskite solar cells.

Abstract

The most studied perovskite-based solar cells reported up to date contain the toxic lead in its composition. Photovoltaic research and development towards non-toxic, lead-free perovskite solar cells are critical to finding alternatives to reduce human health concerns associated with them. Bismuth-based perovskite variants, especially in the form of methylammonium bismuth iodide (MBI), is a good candidate for the non-toxic light absorber. However, the reported perovskite variant MBI thin flms prepared by the solution process so far suffers from poor morphology and surface coverage. In this work, we investigate for the first time the optoelectronic, crystallographic and morphological properties of MBI thin flms prepared via thermal co-evaporation of MAI and BiI3. We find by modifying the precursor ratio that the layer with pure MBI composition lead to uniform, compact and homogeneous layers, broadening the options of deposition techniques for lead-free based perovskite solar cells.