Optimization Of Cd(S,Se) Quantum Dot Photosensitizers For Sensitized Solar Cells

Quantum dot-sensitized Solar Cells（QDSSCs）have attracted much attention due to their advantages of high theoretical efficiency,low cost and simple preparation process.The QDSSCs structure is mainly composed of three parts:photoanode,electrolyte and counterelectrode.Among them,the photosensitizer in the photoanode is the core part of the battery.Due to the shortcomings of single Quantum Dots（QDs）photosensitizer,such as small spectral absorption range and high charge recombination at the interface,the conversion efficiency of QDSSCs is inhibited.To solve these problems,this work takes CdS/CdSe composite QDs sensitizer as the research object,and the specific research content is as follows:（1）The comparative study of existing CdSSe alloy QDs and CdS/CdSe core-shell QDs sensitizers is based on different preparation processes.In this work,a modified continuous ion adsorption and reaction（SILAR）method is proposed.By adjusting the deposition sequence of CdS and CdSe,a series of structures from alloy band to multilayer band and core-shell band are constructed,thereby changing the light absorption characteristics and electron transport characteristics of the photoanode.The results show that CdS/CdSe core-shell is superior to CdSSe alloy,achieving a maximum Power conversion efficiency（PCE）of 5.08%,which is77%higher than CdSSe alloy structure QDSSCs（2.87%）.（2）Metal ion doped QDs changes the recombination dynamics and charge separation of QDs by creating electronic states within the QDs band gap,thereby improving the optical properties of the battery.Based on the CdS/CdSe core-shell QDs structure obtained in work（1）,transition metal Zn²⁺was introduced into the cationic precursor body fluid of CdS/CdSe core-shell QDs prepared by SILAR method,thus achieving Zn-doped CdS/CdSe core-shell QDs.The results showed that when the Zn doping concentration was 1.6%,the prepared QDSSCs obtained 5.59%PCE,compared with the non-Zn doped QDSSCs（4.41%）,PCE increased by 26.76%.Reasons for its enhancement:On the one hand,Zn doping reduces the charge recombination rate at the interface,generates more electrons and increases the Short-circuit current density(J_sc).On the other hand,the high electron concentration of Zn²⁺leads to the increase of Fermi level and the increase of Open-circuit potential(V_oc).（3）On the basis of work（1）and（2）,the transition metal Zn doping of CdSSe alloy QDs is further studied.In this work,Zn-doped CdSSe（Zn-CdSSe）alloy QDs was synthesized by using two step cationic(Cd²⁺)and anion(Se^2-)hydrothermal exchange method using Zn S prepared by SILAR method as template.By improving the reaction time and temperature during the preparation of Zn-CdSSe QDs,the optimal ratio was Zn_0.03Cd_0.97S_0.43Se_0.57,and QDSSCs achieved 3.61%PCE.Compared with CdSSe（2.17%）QDSSCs synthesized by one-step hydrothermal anion(Se^2-)exchange reaction using CdS template,it was 66.35%higher than CDSSE（2.17%）QDSSCs.