Excitation density dependence of photocurrent efficiency in low mobility semiconductors

Abstract

We report numerical simulation of the charge transport in low mobility semiconductors under optical excitation. We choose the low mobility regime as it is typical of organic polymer semiconductor devices. We find that, contrary to common belief, the limiting factor for the photocurrent at high optical excitation density is the onset of space-charge limit and that bimolecular recombination is merely a result of the limited current. We also show that the power dependence of the photocurrent efficiency can be used to deduce which charge-carrier is the slow one and extract its mobility.