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

• Perovskite solar cells with different cathode of Al, Ag and AgAl were fabricated.
• Cells with AgAl alloy retained 90% of the initial PCE values after aging 48 h.
• Cells with AgAl kept the initial Voc during aging 360 h, showing amazing stability.
• The superior stability of cells with AgAl is attributed to the formation of AlOX.
• AlOX formed boosts electron extraction and inhibits moisture encroachment.

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 (VOC) of cells having an AgAl contact was demonstrated, with almost no change in the VOC after 360 h aging under a relative humidity of 10% in air. However, there is an obvious drop in the VOC of the structurally identical perovskite cells with Ag cathode, e.g., an 85% decrease from its initial VOC value for cells aged under the same condition. The enhancement in the PCE of cells with AgAl cathode is attributed to the formation of AlOX, which can improve built-in potential in the cell and allow an effective electron extraction at the PCBM/AgAl cathode interface. An interfacial AlOX interlayer could be formed at the interface between PCBM and AgAl contact during thermal evaporation and aging. The presence of the interfacial AlOX 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.

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