One-step synthesis of aqueous CdTe/CdSe composite QDs toward efficiency enhancement of solar cell

•A one-step method was constructed to synthesize the aqueous CdTe/CdSe composite QDs with over 80% PLQY.•Three types of CdTe/CdSe composite QDs were systematically prepared and compared.•The efficiency of planar crystalline silicon solar cells is improved by 26.83% thanks to PVA/QDs coatings.•The contributions from the antireflective and down-shifting effects were quantified. Aqueous quantum dots (QDs) have been widely used in photovoltaic devices. However, aqueous QDs usually perform poorly in terms of optical properties and stability. In this paper, CdTe/CdSe composite QDs were synthesized in an aqueous solution by a simple one-step method, obtaining the tunable optical properties with a photoluminescence quantum yield (PLQY) over 80%. The simultaneous addition of Te and Se sources passivates the defects of CdTe while suppressing the overgrowth of CdSe shell, obtaining core–shell structure with small size and high PLQY. The PVA/QDs film was prepared by spin-coating to achieve up to 26.83% efficiency improvement on the surface of crystalline silicon solar cells, due to the excellent antireflection and down-shifting effect.