Amazing stable open-circuit voltage in perovskite solar cells using AgAl alloy electrode

The progresses made in emerging perovskite solar cells, a promising alternative photovoltaic technology to the conventional solar cells, have quickly set the power conversion efficiency (PCE) record of 20%. Apart from the high PCE, the stability of perovskite solar cells is another important issue for them to be commercially viable. To investigate the impact of electrodes on the stability of the perovskite solar cells, cells with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Cathode, having different cathode contacts of Al, Ag and AgAl alloy, were fabricated. The cells with an AgAl alloy cathode reached a PCE of 11.76%, which is slightly higher than that (11.45%) of the structurally identical cells with Ag contact, much higher than that for the ones with Al electrode (7.95%). The stable open-circuit voltage (V_OC) of cells having an AgAl contact was demonstrated, with almost no change in the V_OC after 360 h aging under a relative humidity of 10% in air. However, there is an obvious drop in the V_OC of the structurally identical perovskite cells with Ag cathode, e.g., an 85% decrease from its initial V_OC value for cells aged under the same condition. The enhancement in the PCE of cells with AgAl cathode is attributed to the formation of AlO_X, which can improve built-in potential in the cell and allow an effective electron extraction at the PCBM/AgAl cathode interface. An interfacial AlO_X interlayer could be formed at the interface between PCBM and AgAl contact during thermal evaporation and aging. The presence of the interfacial AlO_X interlayer helps to prevent the diffusion of the Ag atoms into the active layer, to improve the adhesion of the metal contact on PCBM and also to avoid moisture encroachment.