Buckled topography to enhance light absorption in thin film organic photovoltaics comprising CuPc/C60 bilayer laminates
Organic photovoltaic (OPVs) devices are promising due to their low cost, light weight, and compatibility with high throughput processing on flexible substrates. This paper demonstrates a simple process utilizing thin-film instabilities to enhance light absorption in OPVs in a way that is compatible with planar processing and the customary thermal annealing steps. Placing a thin, transparent polystyrene (PS) film between the glass substrate and the transparent conductive indium tin oxide (ITO) electrode results in the formation of periodic surface buckles in the PS layer due to induced strain caused by thermal expansion mismatch between the ITO and PS films. OPVs comprising bilayer laminates of copper phthalocyanine (CuPc) and fullerene (C60) deposited onto buckled the ITO/PS substrate show enhanced light absorption due to the longer path-length and improved power conversion efficiency (20%) relative to a similar planar device. This approach is appealing because it takes advantage of naturally-occurring surface topography (i. e., buckling) without the need for any sophisticated patterning. This work is distinguished from other buckling strategies for OPVs by the use of ITO as a transparent, conductive electrode and the absence of additional processing steps.