Photoanode/electrolyte interface modification in solar PEC cells sensitized with Cd0.8Zn0.2S quantum dots for efficient dye degradation

• The molar ratio of Cd to Zn in alloy CdZnS colloid quantum dots as solar sensitizer was optimized through the computation based on modified DFT . • ZnS QDs as passivating layer can inhibit reversed photocurrent and improve the wettability in electrolytes simultaneously. • The degradation mechanism of organic dyes in PEC cells was systematically investigated. • The device expresses high PEC stability that decolorization. Quantum dot (QD) sensitized solar photoelectrochemical (PEC) cells can be used to degrade organic dyes efficiently with the advantages of no secondary pollution and energy conservation. Ternary TiO 2 /Cd 0.8 Zn 0.2 S/ZnS photoanodes in heterojunction structure were designed in PEC cells for degradation of several organic dyes. The molar ratio of Cd to Zn in alloy CdZnS colloid QDs as solar sensitizer was optimized through the computation based on modified DFT to meet carrier transfer thermodynamic requirement in ternary TiO 2 /CdZnS/ZnS photoanode. ZnS QDs as passivation layer can inhibit reverse photocurrent and improve the wettability in electrolytes simultaneously. The TiO 2 /CdZnS/6ZnS photoanode cell device exhibited the current density maximum of 0.3235 mA/cm 2 under one sun (AM 1.5, 100 mw/cm 2 ) and achieved 89 % decoloration rate for methylene blue (MB) after 3-hour degradation at 0.8 V applied bias, comparing with 0.059 mA/cm 2 and 78 % decolorization rate of TiO 2 /CdZnS photoanode cell. Furthermore, the device showed high PEC stability that decolorization rate decreased from 89 % to 84 % after five cycles of 3-hour degradation. The effects of applied bias, ZnS content and dye type on PEC performance and decoloration rate were investigated systematically for clarifying degradation mechanism of organic dyes in PEC cells.