The ultrathin PEALD-GaN surface/interface layer-modulated charge dynamics in quantum dot-sensitized solar cells

In this work, gallium nitride (GaN) is employed for the first time to modulate the charge dynamics of quantum dot-sensitized solar cells (QDSCs). An ultrathin GaN layer has been coated on the surface of both mesoporous TiO 2 photoanode and quantum dots (QDs) at 240 °C by plasma-enhanced atomic layer deposition (PEALD) approach. It is revealed that there exists a stepped energy level alignment among the as-prepared TiO 2 film, GaN layer and QDs, which accelerates the extraction and collection of photogenerated electrons. Meanwhile, a type-II core-shell QD/GaN structure is formed benefiting from the self-limiting reactions of PEALD, resulting in an enhanced light absorption and a redshift of absorption edge. In addition, the dense GaN layer can also effectively inhibit the reverse transfer of photogenerated electrons from TiO 2 to QDs or electrolyte while improving the connection between TiO 2 and QDs. Ultimately, the QDSCs with a 0.68 nm-thick GaN layer achieve a 29% increase of short-circuit current density and enhanced device efficiency, even with reduced fill factor. This work has shown the multi-functions of GaN in regulating the charge dynamics of QDSCs as well as the potential advantages in replacing TiO 2 as photoanode for electronic extraction and transport.