Stability of inverted organic solar cells with low-temperature ZnO buffer layer processed from aqueous solution

In this work, the long-term stability for inverted organic solar cells (OSCs) using a poly(3-hexylthiophene-2, 5-diyl):[6, 6]-phenyl C-61 butyric acid methyl ester blend and a low-temperature ZnO buffer layer processed from aqueous solution is investigated. The same devices with ZnO buffer layers annealed at different temperatures have been sequentially stored in an air-N-2-air environment and tested during 4320h. It is found that the devices with ZnO annealed at 80 and 100 degrees C show good stability in three periods of air, N-2, and air conditions, the degradation of power conversion efficiency (PCE) shows similar tendency to that of short circuit current density with relatively steady open circuit voltage and fill factor. For devices with 70 degrees C annealed ZnO buffer layer, their PCE climbs up and then declines in the first period. Interestingly, at the beginning of third period, an improvement of photovoltaic parameters for most devices is observed from statistical results, which may be related to the change of oxygen concentration in devices and oxygen desorption in light soaking. In short, all devices show a relatively good stability and the simple ZnO deposition method is a promising technique in fabricating inverted OSCs and flexible devices with long lifetime. Degradation of PCE for inverted OSCs in 4320h.