Stability of polymer solar cells: Dependence on working pressure

We investigated the degradation behavior of polymer/fullerene solar cells processed at different working pressures during the deposition of the metal back electrode by physical vapor deposition (PVD). The temporal development of the photovoltaic parameters was determined with a homemade automated degradation setup for constant irradiation of ∼1000 W/m2 in air. itial device efficiency improved with evacuation time. The device stability itself depended also on the PVD working pressure: the larger the PVD pressure, the more pronounced was the fast decay of the performance. As reactive remnants, still present within the evaporation chamber due to the larger PVD working pressure, seemed to contribute to the so-called device “burn-in”, yielding overall stronger decays for larger PVD working pressures. As a consequence a trade-off between final base working pressure and pumping time seems to be a requirement for cost-effective industrial evaporation processes.