The Effect Of Surface Passivation On CdS/CdSe Quantum Dot Sensitized Solar Cells

Since the first industrial revolution,human has been greatly increased productivity,the continuous improvement of productivity is accompanied by mankind's constant pursuit of energy.Traditional fossil energy is still the main source of energy for social industrial development because of its low cost and easy access.However,with the decrease of existing fossil energy and the continuous rise of human demand for energy,the traditional energy supply structure has long been unable to meet the needs of production and living.Solar energy is the most potential new energy because of its huge reserves and wide distribution.Solar cells,as the main use of solar energy,are not limited by space location,and have many advantages such as safety and environmental protection in the power generation process,which has attracted more and more attention of researchers and developers.In all kinds of solar cell,quantum dots sensitized solar cells(QDSSC)have attracted the attention of many researchers due to their simple preparation process,low manufacturing cost and high theoretical efficiency,which is more than 44%.However,quantum dots will cause strong electron hole recombination due to their surface defects,which severely limits the further improvement of the overall efficiency of the cell.On the other hand,the liquid electrolyte of QDSSC is easy to deteriorate and leak,QDSSC cannot be commercially used because of stability.In this paper,the following work is carried out.Surface passivation in quantum dot sensitized solar cells plays a very important role in preventing surface charge recombination and thus enhancing the power conversion efficiency(PCE).ZnS and ZnSe materials have been widely used in CdS/CdSe QDSSC because of their unique energy band structure and good lattice matching with CdS/CdSe quantum dots.The surface modification of quantum dots by ZnS and ZnSe in CdS /CdSe quantum dots co-sensitized solar cells has been proved to be an effective method to reduce leakage current and improve PCE.In this study,solar cells with two different passivation layers were prepared,and a series of characterization comparisons were made on the photoelectric properties and material properties of the cells,so as to further reveal the surface modification and effect of the passivation layer on the QDSSC.However,considering that semiconductor materials ZnS and ZnSe with wide bandgap,cannot effectively absorb and transform photons in infrared range,in order to further improve the PCE of solar cells,this paper dope transition metal to regulate the band gap of quantum dots(QD)materials and effectively explains the experimental results by combining theoretical calculation.In this 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(DFT)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 sample 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 and the PCE of CdS/CdSe co-sensitized QDSSC 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.Considering the future development of portable and practical solar cell devices,this paper also explores the devices with solid-state flexibility.Since the traditional liquid electrolyte is prone to leakage corrosion during the use of the flexible device,the gel electrolyte prepared by the polymer is selected as the cell electrolyte,and finally the flexible carbon cloth electrode is successfully assembled with the PET-ITO photoanode,and the flexible device is successfully assembled.Through process improvement and optimization,the all-solid-state flexible QDSSC achieves considerable PCE.