Enhancement of lead-free perovskite solar cells devices by heat treated bismuth oxyiodide thin films

Lead-free bismuth oxyiodide (BiOI) perovskite solar cells (PSCs) have been successfully fabricated using successive ionic layer adsorption and reaction (SILAR) technique. The effects of heat treatment temperature on thickness, conductivity and microstructure of BiOI thin films have been studied prior to the device fabrication. From SE M result, flower shaped flakes microstructure is obtained in as-deposited BiOI layer and it enlarged as the heat treatment increased up to 350°C, and crushed with higher heat treatment temperature, afterward. This is associated with the trend in conductivity measurement where BiO I achieved the optimum conductivity when it was heat treated at 350°C and reduced as the heat treatment exceeded 450°C. This could be due to the reduction of grain boundaries as a result of development of the flakes sizes during the heat treatment, material sublimation and particles aggregations that developed higher resistance in the BiO l layers. The devices performances under optimum heat treatments have been characterized using I-V measurement under a solar spectrum simulator with A M 1.5 illuminations. BiO l PSCs treated at 350°C showed -6 % efficiency. This study provided better understanding on BiO l thin film behaviors under several heat treatments and its potential to be applied as lead-free PSCs.