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 PbI 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%.