Multi‐Functional MoO<sub>3</sub> Doping of Carbon‐Nanotube Top Electrodes for Highly Transparent and Efficient Semi‐Transparent Perovskite Solar Cells
Seungju Seo, Kosuke Akino, Jeong‐Seok Nam, Ahmed Shawky, Hao‐Sheng Lin, Hiroki Nagaya, Esko I. Kauppinen, Rong Xiang, Yutaka Matsuo, Il Jeon, Shigeo Maruyama
Abstract
Abstract MoO 3 doping of carbon‐nanotube top electrodes in perovskite solar cells is multi‐functional and facilitates p‐doping, favorable energy‐level alignment, and enhanced hole transport. The optimal layer thickness of MoO 3 (8 nm) is determined for decreasing the sheet resistance of carbon‐nanotube electrodes without damaging the perovskite film. The sheet resistance decreases by approximately one‐third from its original value, which is a substantially better result than that previously reported for acid doping of carbon‐nanotube top electrodes. MoO 3 deposition lowers the Fermi level of the carbon‐nanotube electrode, improving its energy‐level alignment and hole‐transfer performance. When coated with 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐MeOTAD), MoO 3 crystallizes on the carbon nanotubes and further enhances hole collection. Semi‐transparent perovskite solar cells with MoO 3 ‐doped carbon‐nanotube electrodes have a power conversion efficiency of 17.3% with a transmittance of approximately 60% (at a wavelength of 1000 nm). Because of their favorable transparency in the infrared region, these perovskite solar cells are evaluated for use in a tandem structure with silicon solar cells via computational simulations. The predicted device efficiency (23.7%) exceeds that of conventional indium‐tin‐oxide‐based tandem solar cells (23.0%).