Zhe Li
Swansea University, U.K
Title: Fullerene oxidation – a key degradation pathway of organic photovoltaiccells
Biography
Biography: Zhe Li
Abstract
Environmental stability is a common challenge for thecommercialisation of low cost, encapsulation-free organic opto-electronicdevices. Understanding the role of materials degradation is the key to addressthis challenge, but most such studies have been limited to conjugated polymers. Here we quantitatively study the role of the common fullerene derivative PCBM in limiting the stability of benchmark organic solar cells, showing that aminor fraction (<1%) of photo-oxidised PCBM, induced by short exposure toeither solar or ambient laboratory lighting conditions in air, relevant to typical processing and operating conditions, is sufficient to compromise device performance severely. We identify the effects of photo-oxidation of PCBM on its chemical structure, and connect this to specific changes in its electronicstructure, which significantly alter the electron transport and recombinationkinetics. The effect of photo-oxidation on device current-voltagecharacteristics, electron mobility and density of states could all be explained with the same model of photoinduced defects acting as trap states. Our resultsdemonstrate that the photochemical instability of PCBM and chemically similarfullerenes remains a barrier for the commercialisation of organicopto-electronic devices.