Power-Law Density of States in Organic Solar Cells Revealed by the Open-Circuit Voltage Dependence of the Ideality Factor
Maria Saladina, Christopher Wöpke, Clemens Göhler, I. Ramírez, Olga Gerdes, Chao Liu, Ning Li, Thomas Heumüller, Christoph J. Brabec, Karsten Walzer, Martin Pfeiffer, Carsten Deibel
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_{oc}) dependence of the ideality factor. By performing Suns-V_{oc} measurements, we find that the energetic disorder increases deeper into the band gap, which is not expected for a Gaussian or exponential DOS. The linear dependence of the disorder on energy reveals the power-law DOS in organic solar cells.