Charge Carrier Concentration and Temperature Dependent Recombination in Polymer Fullerene Solar Cells

TL;DR

This study investigates how charge carrier concentration and temperature influence recombination in polymer-fullerene solar cells, revealing a dynamic trapping mechanism affecting recombination order.

Contribution

It provides new insights into temperature-dependent recombination mechanisms and charge trapping effects in polymer solar cells, supported by combined transient and extraction measurements.

Findings

Recombination prefactor strongly depends on charge concentration and temperature.

Recombination follows an apparent order greater than two due to charge trapping.

Experimental results align with a model involving dynamic trapping in tail states.

Abstract

We performed temperature dependent transient photovoltage and photocurrent measurements on poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methylester bulk heterojuction solar cells. We found a strongly charge carrier concentration and temperature dependent Langevin recombination prefactor. The observed recombination mechanism is discussed in terms of bimolecular recombination. The experimental results were compared with charge carrier extraction by linearly increasing voltage (photo-CELIV) measurements done on the same blend system. We explain the charge carrier dynamics, following an apparent order larger than two, by dynamic trapping of charges in the tail states of the gaussian density of states.