Unravelling the working junction of aqueous-processed polymer-nanocrystal solar cells towards improved performance

Hybrid solar cells (HSCs) based on aqueous polymers and nanocrystals are attractive due to their environmental friendliness and cost effectiveness. In this study, HSCs are fabricated from a series of water-soluble polymers with different highest occupied molecular orbital (HOMO) levels and nanocrystals with different Fermi levels. We demonstrate that the working principle of the aqueous-processed HSCs follows a p-n junction instead of a type-II heterojunction. The function of the polymer is to provide an interface dipole which can improve the build-in potential of the HSCs. Subsequently, the aqueous-processed HSCs are optimized following a p-n junction and an improved PCE of 5.41% is achieved, which is the highest for aqueous-processed HSCs. This study will provide instructive guidelines for the development of aqueous-processed HSCs.