The effect of thermal annealing on defect states, light intensity and photocurrent of organic solar cells

Abstract

Due to the low conversion efficiency and instability, organic solar cells (OSCs) still cannot be compared with conventional silicon-based solar cells that have been produced commercially. The low performance is attributed to the existence of defect states in solar cells. The defect states will prevent the carrier from transporting and then reduce the power conversion efficiency (PCE). In this work, the external quantum efficiency (EQE) measurement and current-voltage (I-V) measurement are used to characterize the performance of OSCs. The experimental results show that the power conversion efficiency of the cells increases from 0.56% to 3.52% after thermal annealing. The relationship between light intensity and photocurrent and the transient photocurrent (TPC) measurement is used to study the effect of annealing on the defect states of OSCs. The relationship between light intensity and photocurrent under different light intensities for cells before and after thermal annealing is compared. It is found that there is a linear relationship between light intensity and photocurrent of the cells after thermal annealing. Analysis of experimental results indicates that thermal annealing could reduce the density of defect states, effectively inhibits carrier recombination, promotes carrier transport, and ultimately improve the performance of cells.