Electronic Doping in Perovskite Solar Cells

The popularity of metal halide perovskites is in part the result of their versatility in numerous applications. To date, perovskites are used in their intrinsic, undoped form, as the doping of these materials is not yet adequately mastered. Herein, the recently reported electronic doping of CH₃NH₃PbI₃ is employed to fabricate perovskite solar cells in which the interfacial electron transport layer (ETL) is replaced by n-doping of one side of the perovskite film. The doping involves the incorporation of metastable Sm²⁺ ions that undergo an in situ oxidation to Sm³⁺, releasing electrons to the conduction band to render the perovskite n-type. In spite of the lack of an ETL, these solar cells have the same efficiency as the samples with the ETL. The open circuit voltage of the doped solar cells increases proportionally to the doping concentration due to the narrowing of the depletion layer thickness at the interface of the perovskite and the top electrode, reaching the value of ≈1 V for the doped ETL-free device, the same as for the reference sample. These proof-of-concept results represent the first step toward perovskite-based devices incorporating a p-n homojunction.