Study On Morphology Control And Surface Impurity Removal Modification Of Absorber Layer Of CZTSSe Solar Cells Based On DMF System

Enhancing the crystallization morphology has been known to effectively improve the PV performances in solution processed copper-zinc-tin-sulfur-selenide(Cu₂ZnSn(S_x,Se_1-x)₄,CZTSSe)solar cells,but it has been technically difficult to implement large-grain spanning monolayer structure because of the complicated coordination,reaction and crystallization processes.In addition,the impurity polymers left by organic ligands in the precursor solution during thermal treatment can deteriorate the device performance.There is no report on the CZTSSe solar cells absorber layer based on the dimethylformamide（DMF）solution system with a large-grain spanning structure.Both the non-large-grain spanning structure and the residual polymer on the surface of the absorber layer will seriously affect the quality of the CZTSSe/CdS interface,which is also the key factor limiting the optoelectronic performance of such solar devices.In this paper,the crystal morphology of CZTSSe was firstly controlled based on the control of pre-annealing temperature and the crystal growth mechanism was studied.Then,the surface of the absorber layer was removed and modified by ultraviolet-ozone（UV-O₃）surface cleaning technology.The research contents are as follows:（1）A new strategy to achieve CZTSSe large-grain spanning monolayer is proposed by taking advantage of the synergistic optimization with a Cu²⁺plus Sn²⁺redox system and pre-annealing temperatures.The effects of different pre-annealing temperatures on the crystallization and film quality of the absorber layer were studied,and the optimum pre-annealing temperature was determined to be 430℃.The growth mechanism of the large-grain spanning monolayer,the effect of the redox reaction rate,and the amount of newly generated crystals at the interface of Mo/CZTSSe based on different pre-annealing temperatures are carefully investigated.Three types of absorber growth mechanisms and a concept of critical temperature are proposed.The device performance test results show that the device with the large-grain spanning structure can effectively suppress the recombination of carriers and improve the shunt resistance(R_sh),carrier recombination resistance(R_ct)and open circuit voltage(V_oc)of the device.The transformation efficiency（PCE）was 10.5%.（2）The surface of the absorber layer was removed and modified using UV-O₃surface cleaning technology,the CZTSSe/CdS interface was optimized.The PCE of the device was increased from an average of 10.2%to 10.95%.The results of the research on the device performance improvement mechanism show that the impurity polymer on the surface of the absorber layer after 15 min UV-O₃ treatment reduces the wettability and improves the subsequent deposition of CdS crystallinity and becomes more flat and dense.UV-O₃ treatment reduces the surface work function of the absorber without damaging the surface of the absorber,which eventually leads to the enhancement of the built-in electric field and the improvement of R_ct.The carrier separation ability of the CZTSSe/CdS interface is enhanced and the recombination resistance is increased,the carrier concentration of the device is increased,R_sand R_sh improved while V_oc and short circuit current density(J_sc)improved,and the device with a PCE of up to 11.2%is obtained.This paper has 46 figures,8 tables,and 111 references.