Novel NiO Nanoforest Architecture for Efficient Inverted Mesoporous Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) demonstrate attractive features in developing an air-stable photovoltaic device, by employing inorganic hole transport layers (HTLs). However, their power conversion efficiencies are still inferior to that of mesoporous n-i-p devices, mainly attributed to the undesirable hole extraction and interfacial recombination loss. Here, we design a novel one-dimensional NiO nanotube (NT) nanoforest as efficient mesoporous HTLs. Such a NiO NT mesoporous structure provides a highly conductive pathway for rapid hole extraction and depresses interfacial recombination loss. Furthermore, excellent light capturing could be achieved by optimizing the length and branch growth of the NiO NT nanoforest, which mimics the evolution of the natural forest. Therefore, this inverted mesoporous PSCs yield an optimal efficiency of 18.77%, which is still prominent in state-of-the-art NiO-based devices. Alternatively, the mesoporous device exhibits greatly improved long-term stability. This work provides a new design perspective for developing high-performance inverted PSCs.