Degradation of Flexible, ITO-Free Oligothiophene Organic Solar Cells

摘要

We investigate the degradation of organic solar cells based on an oligothiophene (DCVST-Me) small molecule donor and the acceptor C-60. Two different flexible, transparent bottom electrode types are employed: a transparent metal electrode (TME) and silver nanowires (AgNWs). They exhibit high optical transparency up to 86% and a sheet resistance as low as 12 Omega/square. Power conversion efficiencies: of 7.0%, 5.7%, and 7.2% on TME, AgNWs, and indium tin oxide (ITO, reference) are reached; respectively. The solar cells are protected against moisture ingress utilizing a flexible alumina thin-film, exhibiting water vapor transmission rates down to 3 x 10(-5) g m(2) day(-1) at 38 degrees C and 90% relative humidity (RH). Implementation of this ultrabarrier as top and bottom encapsulation enables fabrication of fully flexible devices. A decrease in PCE to 80% of initial values is observed after 1000 +/- 50 h on flexible, encapsulated TME but only 20 +/- 5 h on AgNWs in a climate of 38 degrees C/50% RH. Degradation in AgNW-based devices is attributed to electrode decomposition.