Structure-function relationships of fullerene esters in polymer solar cells: unexpected structural effects on lifetime and efficiency

TL;DR

This study investigates how small structural variations in fullerene esters affect the efficiency and lifetime of polymer solar cells, revealing unexpected effects and emphasizing the importance of a diverse molecular library for optimization.

Contribution

It demonstrates that minor structural differences in fullerene esters can significantly impact device performance and lifetime, highlighting the value of a library approach for material optimization.

Findings

Minor structural changes cause large efficiency differences

Isomeric R-groups lead to different device efficiencies

Transport and spectroscopic lifetimes are generally aligned

Abstract

We report both transport measurements and spectroscopic data of polymer/fullerene blend photovoltaics using a small library of fullerene esters to correlate device properties with a range of functionality and structural diversity of the ester substituent. We observe that minor structural changes can lead to significant differences in device efficiency and lifetime. Surprisingly, we have found that isomeric R-groups in the fullerene ester-based devices we have studied have very different efficiencies. The characteristic lifetimes derived from both transport and spectroscopic measurements are generally comparable, however some more rapid effects in specific fullerene esters are not observed spectroscopically. Our results support using a library approach for optimizing device performance in these systems.