Impacts of Mn ion in ZnSe passivation on electronic band structure for high efficiency CdS/CdSe quantum dot solar cells†
Surface passivation in quantum dot-sensitized solar cells (QDSSCs) plays a very important role in preventing surface charge recombination and thus enhancing the power conversion efficiency (PCE). ZnSe passivation with dopant in CdS/CdSe co-sensitized QDSSCs has been demonstrated as an effective way to improve the PCE. In the present study, a series of characterizations revealed that a Mn-doped ZnSe passivation layer can not only reduce surface charge recombination, but also enhance light harvesting. By means of density functional theory calculation along with a systematic study of electronic band structure, it has been found that the valence band of ZnSe moves upward on Mn-ion doping which leads to acceleration of charge separation and broader light absorption range. The impact of the Mn ion on charge recombination and light harvesting has been interpreted reasonably and the PCE of CdS/CdSe co-sensitized QDSSCs with Mn-doped ZnSe passivation layer is as high as 6.46%, which is 1.5 times that of the solar cell without the passivation layer.