Toward high-performance semitransparent perovskite solar cells: interfacial modification and charge extraction perspectives

Realization of efficient charge extraction at the cathode and anode interfaces is still one of the challenges for improving the power conversion efficiency (PCE) of the semitransparent perovskite solar cells (PSCs). In this work, we report our effort to enhance the PCE of semitransparent PSCs by incorporating a pair of an energetically favorable cathode buffer layer (CBL) and a hole-transporting layer (HTL). The effects of different CBLs, e.g., bathophenanthroline, bathocuproine, and perylene diimide, on charge extraction efficiency and PCE of the semitransparent PSCs are analyzed. Scanning electron microscopy reveals that UV-plasma-treated poly(bis(4-phenyl) (2,4,6-trimethylphenyl) amine) (PTAA) HTL surface favors the growth of a uniform and dense functional CH₃NH₃(I_0.75Br_0.15)₃ perovskite layer across the substrate, with a low defect density for suppressing charge recombination loss. An average PCE of 13.53% and 9.92% was obtained with combination of a bathocuproine CBL and a PTAA HTL measured from the indium tin oxide (ITO) side and Ag side, respectively. Semitransparent PSCs possess an encouraging large average open-circuit voltage of 1.13 V, and an average transparency of 21%. Achieving an efficient charge collection and retaining a high built-in potential across the CH₃NH₃(I_0.75Br_0.15)₃ photoactive layer via interfacial modifications are a prerequisite for attaining high-performance semitransparent PSCs.