Combined influence of Urbach’s tail width energy and mobility of charge carriers on the photovoltaic performance of bulk heterojunction organic solar cells

Bulk heterojunction organic solar cells with four different Urbach’s tail width energies (E _U ) are simulated, and the combined influence of E _U and charge carrier mobility on the short circuit current (J _sc ) , open circuit voltage (V _oc ) , fill factor (FF), power conversion efficiency (PCE), Langevin and tail state recombination is investigated. The results show that J _sc decreases more drastically with increasing E _U in the lower mobility range and then asymptotically converges to a single value in the large mobility range. Likewise, with the increase in mobility, V _oc decreases nearly linearly with different slopes depending on different E _U in the lower mobility range and then different slopes converge to a single slope in the larger mobility range. Thus, V _oc becomes E _U independent in the higher mobility range. Furthermore, it is found that by increasing E _U , the maximum values of FF and PCE shift towards the higher mobility range. It is shown that the influence of combined optimization of E _U and mobility enhances both FF and PCE, but its effect on FF is much more significant than that on PCE.