Degradation of Flexible, ITO-free Oligothiophene Organic Solar Cells.

We investigate the degradation of organic solar cells based on an oligothiophene small molecule donor (DCV5T-Me) and the acceptor C60. 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 Ω/□. Power conversion eciencies 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 vapour transmission rates down to 3*10(-5) g/(m(2)d) at 38 °C and 90 % relative humidity (RH). Implementation of this ultra-barrier as top and bottom encapsulation enables fabrication of fully-flexible devices. A decrease in PCE to 80% of initial values is observed after (825±10) h on flexible encapsulated TME but only (20±5) h on AgNWs in a climate of 38 °C / 50 % RH. Degradation in AgNW-baseddevices is attributed to electrode decomposition.