Enhancement of the electron transportation in the perovskite solar cells via optimizing the photoelectric properties of electron transport layer with nitrogen-doped graphene quantum dots

The electron transport layer (ETL) is an indispensable functional block of perovskite solar cells (PSCs), which plays a pivotal role in the extraction and transportation of photogenerated carriers. In this work, we propose high-performance PSCs with the ETL constructed by the composites of titanium dioxide (TiO 2 ) and nitrogen-doped graphene quantum dots (NGQDs), which are prepared with different ratios of precursor citric acid and urea. Depending on the nitrogen doping ratio, the content of pyridinic nitrogen exhibits a noticeable effect on the photoluminescence and Ultraviolet–Visible light absorption of NGQDs. When the nitrogen doping ratio of NGQDs is 8.29%, the bottom position of the conduction band of the composite films (− 3.93 eV) is comparable to that of MAPbI 3 (− 3.95 eV). With the increased nitrogen doping ratio of NGQDs, the carrier concentration of composite films gradually increases from 4.9 × 10 19 to 1.1 × 10 20 cm −3 , and the built-in electric field is simultaneously enhanced, resulting in greatly accelerated carrier extraction and effectively blocked hole transportation to ETL. At a proper doping ratio, the photoelectric conversion efficiency of fabricating devices increases by 14.81% from 12.69 to 14.57%.