Enhancing efficiency of MAPbI3 perovskite solar cells with carbon quantum dot implanted g-C3N4: Controllable crystallization and surface passivation

Organic-inorganic hybrid perovskite films with excellent surface morphology and large grain sizes are crucial for achieving high-performance perovskite solar cells (PSCs). To reduce production costs and meet the growing demand for lightweight thin solar cells, developing ultra-thin absorber layers is an effective approach. However, defects and trap sites are inevitably formed on the surfaces of solution-processed perovskite films. Herein, we present an innovative method that directly incorporates graphite carbon nitride/carbon quantum dots (g-C 3 N 4 /CQDs) into the perovskite precursor solution, using them as structural template to modulate film growth. The g-C 3 N 4 /CQDs delay crystallization through the formation of a MA·g-C 3 N 4 /CQDs intermediate adduct, which reduces light absorption loss by increasing enlarge grain size and minimizing numerous pinhole defects in thin perovskite films. Additionally, the amide bond formed between g-C 3 N 4 and CQDs can accelerate charge transport, as demonstrated by density functional theory calculation. As a result, the PSCs based on high-quality 360 nm MAPbI 3 :g-C 3 N 4 /CQDs films achieved a champion power conversion efficiency of 20.49 %. The devices retained more than 90 % of their initial efficiency for over 500 h in air without encapsulation. This work not only provides valuable insights into the role of 2D/0D carbon-based heterojunctions in PSCs, but also provides a straightforward technique for crystallization regulation to achieve efficient and stable PSCs.