Enhanced Thermal Stability of Inverted Polymer Solar Cells Based on Solution-Processed WOx as an Anode Interlayer

The simultaneous optimization of device efficiency, stability and large area processing represents one of the biggest challenges to exploit the potential offered by polymer solar cells. In this context, detailed studies of the impact of different interlayers on the key device properties are of crucial importance. Herein, the thermal stability of inverted polymer solar cells containing two different metal oxides as an anode interlayer is compared: i) ?80 nm of solution-processed tungsten oxide (WOx) and, ii) 10 nm of (thermally evaporated) molybdenum oxide (MoOx) as a reference system. A detailed comparison focused on the evolution of device performances/properties before and after thermal stress (85?C for 140 h in dark) is reported, highlighting advantages arising from the use of WOx as an interlayer. Two sets of inverted solar cells, based on either HBG-1:PC61BM and P3HT:PC61BM as active layer, are fabricated and studied. Electrical, morphological and optical characterizations, performed both on freshly prepared and aged devices, are analyzed and correlated to explain the positive effect of the WOx interlayer on the resulting device thermal stability. Compared to fresh devices, thermally aged WOx (MoOx) based HBG-1:PC61BM and P3HT:PC61BM solar cells exhibit an efficiency decay of -16% (-24%) and -28% (-57%), respectively.