Order of Decay of Mobile Charge Carriers in P3HT:PCBM Solar Cells

TL;DR

This study investigates the decay order of mobile charge carriers in P3HT:PCBM solar cells, revealing how oxygen exposure affects trap states and recombination mechanisms, which are crucial for understanding and improving device performance.

Contribution

It introduces a method to derive the recombination order of mobile charge carriers and links it to trap state energies and recombination processes in organic solar cells.

Findings

Recombination order decreases slightly after oxygen exposure.

Trap state energy increases from 40 meV to 100 meV.

Recombination shifts towards trap-assisted mechanisms.

Abstract

The charge carrier dynamics of organic solar cells are strongly influenced by trapping and allow to draw conclusions on the loss mechanisms limiting the photovoltaic performance. In this study we derive the recombination order \Delta\ of mobile charge carriers. For annealed P3HT:PCBM solar cells, it allows us to pinpoint the dominant recombination of mobile with trapped charge carriers in tail states. While the characteristic tail state energy of about 40 meV rises to about 100 meV for 30 h oxygen exposure under illumination, \Delta\ decreases only weakly from 1.70 to 1.62: This corresponds to a slight shift towards trap-assisted recombination.