Graphene doping improved device performance of ZnMgO/PbS colloidal quantum dot photovoltaics

Lead sulfide (PbS) colloidal quantum dots (CQDs) solar cells possess the advantages of absorption into the infrared, solution processing, and multiple exciton generation, making them very competitive as a low-cost photovoltaic alternative. Employing an n-i-p ZnO/tetrabutylammonium (TBAI)-PbS/ethanedithiol (EDT)-PbS device configuration, the present study reports a 9.0% photovoltaic device through ZnMgO electrode engineering and graphene doping. Sol-gel-derived Zn_0.9Mg_0.1O buffer layer shows better transparency and higher conduction band maximum than ZnO, and incorporation of graphene and chlorinated graphene oxide into the TBAI-PbS and EDT-PbS layer respectively boosts carrier collection, leading to device with significantly enhanced open circuit voltage and short-circuit current density. It is believed that incorporation of graphene into PbS CQD film as proposed here, and more generally nanosheets of other materials, would potentially open a simple and powerful avenue to overcome the carrier transport bottleneck of CQD optoelectronic device, thus pushing device performance to a new level.