Trap-assisted recombination in disordered organic semiconductors extended by considering density dependent mobility

Understanding recombination processes in organic semiconductors is fundamental in modeling solar cells and lighting diodes. However, recognition on recombination processes is still controversial. In this work, the trap-assisted Shockley-Read-Hall (SRH) recombination proposed by Kuik et al. (2011) is modified by considering three factors. The first one is the density of state (DOS) for recombination centers in SRH process, the second one is the trapped charges of recombination centers in Poisson equation, the third one is the density dependence of mobility. The modified model is applied to typical devices with experimental data about open circuit voltage (Voc) with light intensity (Pin) which having been used to distinguish recombination processes. These Voc − log(Pin) data previously were explained by using the Langevin recombination, or SRH recombination, or mixing of both recombinations. The results show that these experimental data can be uniformly well fitted and explained by using the modified SRH model. The DOS for recombination centers is not important, but the density dependence of mobility is very important in arriving good fittings. The influence of Langevin recombination is compared, and is shown not enough to explain the saturation effects in Voc − log(Pin) curves at high light strength, if neglecting the density dependence of mobility.