PCBM

PCBM, short for [6,6]-phenyl-C61-butyric acid methyl ester, is a functionalized fullerene derivative widely used as an electron acceptor in organic photovoltaics and other organic electronic applications. It is a mono-adduct of the C60 fullerene with a phenylbutyric acid methyl ester substituent at a [6,6]-bond, which provides the molecule with a fullerene cage for electron acceptance and a flexible side chain to improve solubility and processability.

Properties of PCBM include a relatively high electron affinity and good electron mobility within the fullerene framework, along with solubility in common organic solvents such as chlorobenzene and o-dichlorobenzene. In organic solar cells, PCBM accepts electrons from donor polymers after photoexcitation, forming a bulk heterojunction that promotes charge separation and transport to electrodes. It is commonly blended with donor materials such as P3HT or other conjugated polymers in weight ratios that optimize morphology and device performance. PCBM can be used in conjunction with PC70BM, a C70-based analogue that offers broader absorption.

In the context of device architecture, PCBM-based solar cells typically employ a planar or bulk-heterojunction structure with a transparent top electrode and a bottom electrode, utilizing interlayers to improve charge extraction. Although PCBM-based systems achieved significant efficiencies in early organic photovoltaics, many recent devices have shifted toward non-fullerene acceptors that can offer higher stability and efficiency. Nonetheless, PCBM remains a standard reference material in research and a benchmark for comparing newer acceptors.

Synthesis of PCBM generally involves a Bingel-type cyclopropanation of C60 with a malonate derivative bearing a phenylbutyric acid methyl ester, followed by hydrolysis and esterification to yield the methyl ester. The related PC70BM uses C70 fullerene to extend the absorption spectrum.