Photovoltaic enhancement of bismuth halide hybrid perovskite by N-methyl pyrrolidone-assisted morphology conversion

Abstract

Low toxicity and highly stable methylammonium bismuth iodide (MBI) ((CH₃NH₃)₃Bi₂I₉) as a solution-processable photovoltaic absorber produces hexagonal non-uniform morphology leading to poor interfacial contacts with the electron and hole transporting layers. Herein, we tuned the morphology of MBI perovskite by bringing in a small amount of N-methyl-2-pyrrolidone (NMP) as a morphology controller into the MBI–DMF solution. The incorporation of various concentrations of NMP into the precursor solution was found to control the rate of crystallization. An optimal low concentration of 2.5% NMP added to the MBI–DMF precursor solution showed a 50% enhancement in short-circuit current (J_sc). The device showed power conversion efficiencies up to 0.31% with high reproducibility. Moreover, the devices were quite stable when exposed to an ambient atmosphere (relative humidity of 50–60%) for 30 days.