Hysteresis-free multi-walled carbon nanotube-based perovskite solar cells with a high fill factor

Among the various perovskite solar cells, the carbon-based hole-transporter-free type is arguably the most promising for applications because of its low material/manufacturing cost, high efficiency and better long-term stability. However, the fill factor (FF) is typically below 0.75, limiting the cell performance. In this communication, through a comparison of systematic performance between the multi-walled carbon nanotube (MWCNT) and another two representative carbon materials, namely carbon black and graphite, we highlight two salient advantages of MWCNT-based devices: high FF and hysteresis-free performance. We owe the superior performance to the charge transport highway at the interface of MWCNT/perovskite. After preliminary optimization, we have achieved a PCE of 12.67% with a very impressive FF of 0.80, which is among the highest for carbon-based perovskite solar cells.