Photoinduced C70 radical anions in polymer:fullerene blends

TL;DR

This study investigates photoinduced charge separation in polymer-fullerene blends, revealing unique spectroscopic signatures of C70 radical anions and their role in charge dynamics, advancing understanding of organic photovoltaic materials.

Contribution

It provides the first detailed spectroscopic analysis of C70 radical anions in polymer blends, highlighting their distinct signatures and charge separation behavior compared to C60.

Findings

C70 radical anions exhibit unique ESR signals at g≥2.005.

A subgap PIA band at 0.92 eV indicates C70 radical anion formation.

C70-based blends show distinct spectroscopic features not present in C60 blends.

Abstract

Photoinduced polarons in solid films of polymer-fullerene blends were studied by photoluminescence (PL), photoinduced absorption (PIA) and electron spin resonance (ESR). The donor materials used were P3HT and MEH-PPV. As acceptors we employed PC60BM as reference and various soluble C70-derivates: PC70BM, two different diphenylmethano-[70]fullerene oligoether (C70-DPM-OE) and two dimers, C70-C70 and C60-C70. Blend films containing C70 revealed characteristic spectroscopic signatures not seen with C60. Light-induced ESR showed signals at g\geq2.005, assigned to an electron localized on the C70 cage. The formation of C70 radical anions also leads to a subgap PIA band at 0.92 eV, hidden in the spectra of C70-based P3HT and MEH-PPV blends, which allows for more exact studies of charge separated states in conjugated polymer:C70 blends.