Perovskite precursor concentration for enhanced recombination suppression in perovskite solar cells
Sabastine C. Ezike, A. D. Ahmed, Raphael M. Obodo, Mufutau A. Salawu
Abstract
Perovskite is a light harvesting material with general structure of ABX3, where A is a monovalent cation (methylammonium (MA+), formamidinium (FA+), caesium (Cs+)), B is a divalent metallic cation (lead (Pb2+)or (Sn2+)) and X is a halide (iodine (I−), bromine (Br−) or chlorine (Cl−). Perovskite precursor concentration was varied from 30 wt% to 60 wt% at step size of 5 wt% and deposited via one-step spin coating of lead iodide (PbI2) and methylammonium iodide (CH3NH3I) at 3:1 M ratio. The effects of precursor concentration on the quality of films and devices fabricated were determined through optical, micro-structural, structural, electrochemical and electrical analyses. The optical characteristics show that 40 wt% is the optimized sample. The micro-structural analysis reveals increase in grain size as the concentrations increases from 30 wt% to 40 wt% and decrease as precursor concentration further increased from 45 wt% to 60 wt%. XRD patterns indicate increase in peaks intensity as the concentration increases from 35 wt% to 40 wt%. However, decrease in peak intensities occurs as the concentration increases beyond 40 wt%. Electrochemical (cyclic voltammetry and electrochemical impedance spectroscopies (EIS)) analyses reveal optimal suppression of carrier recombination by 40 wt% device, which is attributed to presence of larger grain size. The champion cell (40 wt% device) shows 12.43% power conversion efficiency (PCE). Optimization of precursor concentration provides an effective way for suppressing surface charge recombination due to trap-assisted recombination in perovskite devices thereby enhancing the quality and performance of perovskite solar cells.