Electrochemical Design of Nanostructured ZnO Charge Carrier Layers for Efficient Solid-State Perovskite-Sensitized Solar Cells

The preparation of ZnO structured films designed to act as electron transport layers in efficient ZnO/perovskite CH(3)NH(3)Pbl(3)/spirobifluorene (spiro-OMeTAD) solid-state solar cells by electrochemical deposition is reported. Well-conducting ZnO layers are deposited in chloride medium and grown with tailored (nano) structures ranging from arrays of nanowires to a compact, well-covering film. Moreover, the effect of a thin intermediate overlayer of ZnO conformally electrodeposited in nitrate medium and with a low n-type doping (i-ZnO) is discussed. The results show higher power conversion efficiencies for the nanostructured oxide layers compared to the dense one. Moreover, the presence of the i-ZnO layer is shown to markedly improve the cell short-circuit current and the open-circuit voltage due to charge recombination reduction. For the best cells, the active layers efficiently absorb light over a large spectral range from near-UV to near infrared region and exhibit excellent charge collection efficiencies. Solar cells based on an optimized design generate a very large photocurrent and the power conversion efficiency at one sun is as high as 10.28%.