Power-law density of states in organic solar cells revealed by the open-circuit voltage dependence of the ideality factor

TL;DR

This study reveals that the density of states in organic solar cells follows a power-law distribution, determined through temperature and open-circuit voltage dependence of the ideality factor, advancing understanding of disordered semiconductors.

Contribution

It introduces a method to evaluate the DOS in organic solar cells using Suns-$V_ ext{oc}$ measurements and shows the power-law nature of the DOS.

Findings

DOS width increases linearly with DOS depth

Gaussian and exponential distributions only describe DOS at specific quasi-Fermi levels

Power-law DOS characterizes the organic semiconductor materials

Abstract

The density of states (DOS) is fundamentally important for understanding physical processes in organic disordered semiconductors, yet hard to determine experimentally. We evaluated the DOS by considering recombination via tail states and using the temperature and open-circuit voltage ($V_\mathrm{oc}$) dependence of the ideality factor in organic solar cells. By performing Suns-$V_\mathrm{oc}$ measurements, we find that gaussian and exponential distributions describe the DOS only at a given quasi-Fermi level splitting. The DOS width increases linearly with the DOS depth, revealing the power-law DOS in these materials.