Influence of Functionalized Fullerene Structure on Polymer Photovoltaic Degradation

TL;DR

This study investigates how different functionalized fullerene structures affect the degradation rates of polymer photovoltaic devices, revealing that PCBOD significantly enhances stability compared to PCBM.

Contribution

It demonstrates that the chemical structure of fullerene acceptors influences device longevity, with PCBOD providing markedly improved stability over PCBM.

Findings

PCBOD blends show 10-100 times longer device lifetime than PCBM.

Degradation follows an exponential decay pattern for PCBM.

Spectroscopic data correlates with device performance degradation.

Abstract

The time dependence of device performance has been measured for photocells using blends containing the conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with two different functionalized C60 electron acceptor molecules: commercially available [6,6]-phenyl C61 butyric acid methyl ester (PCBM) or [6,6]-phenyl C61 butyric acid octadecyl ester (PCBOD) produced in this laboratory. Performance was characterized by the short-circuit current output of the devices, with the time dependence of PCBM samples typically degrading exponentially. Variations in the characteristic lifetime of the devices were observed to depend on the molar fraction of the electron acceptor molecules (calculated with respect to the MEH-PPV monomer fraction). In comparison to the PCBM samples, the stability of the PCBOD blends was significantly enhanced, with a one or two order of magnitude improvement. Corresponding spectroscopic data with similar time evolution as the transport measurements suggests an independent means for determining and understanding degradation mechanisms.