In situ graphene doping as a route toward efficient perovskite tandem solar cells

Tandem solar cells consisting of perovskite and silicon absorbers have the potential to outperform respective state-of-the-art single junction efficiencies. However, their development requires the gentle deposition of a transparent electrode onto the hybrid perovskite and its organic layers. Implementation of large area graphene obtained by chemical vapor deposition seems to be an excellent solution. In this paper, we present the impact of graphene on perovskite solar cells and their organic layers. Direct application of graphene on CH3NH3PbI3 is limited by a highly defective interface but insertion of spiro-OMeTAD enables a defect free implementation. Solar cells containing transparent graphene contacts approach identical electrical performance compared to devices with standard Au contacts. Hall-effect measurements of graphene on various organic thin-films, revealed the importance of field-effect doping. Gained knowledge enabled the development of a strategy to increase the charge carrier density in graphene by 60%, while lowering graphene sheet resistance by 24%. This combined route of spiro-OMeTAD and stabilized adsorbent doping is an important step toward the targeted application in high performance monolithic perovskite/silicon tandem solar cells. [GRAPHICS] (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim