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 TiO2 photoanode and quantum dots (QDs) at 240 degrees C by plasma-enhanced atomic layer deposition (PEALD) approach. It is revealed that there exists a stepped energy level alignment among the as-prepared TiO2 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 TiO2 to QDs or electrolyte while improving the connection between TiO2 and QDs. Ultimately, the QDSCs with a 0.68 nm-thick GaN layer achieve a 29% in-crease 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 ad-vantages in replacing TiO2 as photoanode for electronic extraction and transport.