Effect of nitrogen plasma on nickel oxide hole transport layer in perovskite solar cells

Abstract

In past few years, perovskite solar cell shows meteoric rise in solar to electric power conversion efficiency (PCE). Based on long diffusion length and almost ideal bandgap, perovskite solar cell improves energy efficiency. Recently, perovskite solar cell with inverted structure has attracted more attention because of easy-fabrication, cost-effectiveness, and suppressed hysteresis characteristics. Based on these advantages, researches to improve performance and stability have been conducted. In this regard, nickel oxide is used as hole transport layer in inverted perovskite solar cell. But stoichiometric nickel oxide has bad conductivity (~10-13 S/cm). So, it must be very thin layer or be doped to transport hole. In general, monovalent cation or copper ion is used as dopant. But these dopants make strain which comes from ionic radius difference. Strain can be reduced when nitrogen substitute oxygen site. Compared to other dopants, nitrogen has smaller mismatch of ionic radius. Therefore, nitrogen doped nickel oxide layer was fabricated as hole transport layer in inverted solar cell to improve conductivity of inorganic layer and structural stability. In this study, nickel oxide layer is formed at relatively low temperature. Through unusual anionic doping, hole conductivity increases compare to pristine nickel oxide. Based on this, it was applied to hole transport layer in perovskite solar cell, resulting an improvement in short-circuit current without structural or morphological change.