Air stable polymer photovoltaics based on a process free from vacuum steps and fullerenes

A polymer solar cell that can be stored under ambient conditions (25 °C and 35±5% relative humidity) in the dark for 6 months without noticeable degradation in performance is presented. The active layer is based on low-cost materials and is free from fullerenes. No vacuum steps are required for processing the device that employs an inverted device geometry, where the active layers in the device comprise a transparent cathode based on solution processed zinc oxide, an active layer based on a bulk heterojunction of zinc oxide nanoparticles and poly-(3-carboxydithiophene) (P3CT), a PEDOT:PSS layer and finally a printed silver based anode. No encapsulation was employed and the devices were robust and not sensitive to mechanical handling of the active layer and back electrode. The accelerated lifetime in air defined as 80% of the initial performance at continuous illumination (1000 W m−2, AM1.5G, 72±2 °C, ambient atmosphere, 35±5% humidity) was typically 100 h and the devices were tested for 150 h. When keeping the same conditions and lowering the temperature, stable operation for hundreds of hours was possible. In terms of long-term stability, this performance is inferior to inorganic photovoltaics but the technology compares well and competes with small batteries in terms of capacity. The device efficiency more than doubled upon decreasing the incident light intensity from 1000 to 100 W m−2.