Polaron Recombination in Pristine and Annealed Bulk Heterojunction Solar Cells

TL;DR

This study investigates polaron recombination losses in P3HT:PCBM solar cells, revealing significantly reduced recombination rates in pristine and annealed devices, which impacts their efficiency.

Contribution

The paper provides experimental evidence of reduced bimolecular recombination rates in both pristine and annealed bulk heterojunction solar cells, supported by a macroscopic device model.

Findings

Recombination rate is reduced by a factor of about ten in pristine devices.

Recombination rate is reduced by a factor of about 25 in annealed devices.

Lowered recombination rates influence the performance characteristics of the solar cells.

Abstract

The major loss mechanism of photogenerated polarons was investigated in P3HT:PCBM solar cells by the photo-CELIV technique. For pristine and annealed devices, we find that the experimental data can be explained by a bimolecular recombination rate reduced by a factor of about ten (pristine) and 25 (annealed) as compared to Langevin theory. Aided by a macroscopic device model, we discuss the implications of the lowered loss rate on the characteristics of polymer:fullerene solar cells.