Boosting the cell efficiency of CdSe quantum dot sensitized solar cell via a modified ZnS post-treatment

• Large improvement of the cell efficiency of CdSe QDSSC was achieved through a modified ZnS post-treatment by introducing a ZnSe in between CdSe QDs and ZnS
• The introduction of ZnSe in post-treatment increased the cell stability.
• The thickness of ZnSe was found to be crucial.
• The role of ZnSe is ascribed to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality.

We report here a large improvement of cell performance of CdSe quantum dot sensitized solar cell (QDSSC) by a modified ZnS post-treatment, being carried out by introducing a ZnSe thin layer before ZnS deposition through a successive ion layer adsorption reaction (SILAR) method. CdSe quantum dots were deposited onto TiO2 surface using a chemical bath deposition method. Photovoltaic measurements showed that the introduction of ZnSe layer can significantly increase the photocurrent of CdSe QDSSC, resulting in a large enhancement of the solar energy conversion efficiency of the cell. On variation of the numbers of ZnSe deposition cycle, the effect of the thickness of ZnSe was investigated. The maximum energy conversion efficiency of 3.46% was achieved for CdSe QDSSC with ZnSe/ZnS treatment, showing a 22% increment compared to that of with ZnS treatment. Moreover, it was found that the introduction of ZnSe improved the stability of CdSe QDSSC. The benefit role of ZnSe was ascribed to its intermediate lattice parameter to CdSe and ZnS, which leads to the suppression of defects at CdSe/ZnS interfaces and facilitating the growth of ZnS with higher quality.

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