Solution-processed electron transport layer of n-doped fullerene for efficient and stable all carbon based perovskite solar cells

Carbon-based perovskite solar cells (PSCs) without hole transport layer (HTL) have shown great prospect for practical applications because of their high stability and low cost. However, almost all of the carbon based PSCs reported so far are fabricated using titanium dioxide (TiO₂) as the electron transport layer (ETL) that requires a rather high-temperature sintering process (500 °C). Moreover, they also suffer from obvious voltage-current hysteresis and conspicuous performance decline under operating conditions. Herein, we report a new type of low-temperature all carbon based PSCs using solution-processed hexamethonium bromide (HMB)-doped C₆₀ as ETL, which achieved a high power conversion efficiency (PCE) of over 16% without the above-mentioned hysteresis. It is shown that doping of C₆₀ with HMB carries several outstanding advantages, including faster charge transport, enhanced electron mobility, and the decreased electron trap density. More encouraging is the remarkable stability of the PSCs fabricated with HMB-doped C₆₀ ETL, which can maintain nearly 90% of their initial performance after continuous operation for 338 hours at their maximum power point under one sun illumination in ambient air.