Study Of Cu₂ZnSn(S_x,Se_1-x)₄Thin Films Fabricated By Substitution Of Chalcogen Elements

Photovoltaic technology is the core technology of energy in the future, and willprovide clean and sustainable energy support for social development. With moreselectivity of substrate, less amount of material, and significantly reducing cost ofbattery, thin film solar cell has a broad application prospects, and is a key target of thesecond-generation solar cells. Because of high theoretical conversion efficiency,richness of raw material, being environmentally friendly and a great cost advantage,CZTS series thin film solar cell has being vigorously researched worldwide. As leaderin research of CZTS series thin film solar cell, Mitzi team at IBM corporation reportedexperimental efficiency exceeding11.1%of CZTSSe thin solar cell.We have prepared metallic precursor of Cu, Sn and Zn with beam evaporation,and then fabricated CZTS thin film having a single crystalline phase, high density ofgrains and strong adhesion to substrate with annealing of the precursor in atmosphereof S. The fabrication depends largely on innovative method of intermittent evaporationof Zn raw material, because the method successfully controlled the evaporation rate. Inseries material of CZTS, as absorbing layer, CZTSSe material has the highestconversion efficiency, so we firstly prepared CZTSSe thin film using simultaneoussulfurization and selenization, according to result, we have obtained CZTSSe thin filmwith greater grain size, better crystallization and adhesion to substrate to be improved.This method has a great research and application value. On this basis, andsystematically taking advantage of theory of generating CZTSSe grain with alternativemethod of S group elements, we comprehensively studied characteristics of CZTS,CZTSe and CZTSSe thin films prepared by sulfurization, selenization, simultaneoussulfurization and selenization, first sulfurization then selenization and firstselenization then sulfurization. With results, we found that Se elements promote graingrowth though the role of mobile phase, and content of Se element directly determineslattice structure. With pre-annealing treatment of metallic precursor within Aratmosphere, we found that pre-annealing not only promotes diffusion of Cu, Sn and Zn, but also increases distance of atoms and is beneficial to film growth by S groupelements into interior of film. With uniform growth in entire interior of film, thin filmwith greater adhesion to substrate, high density of grains and formation has beenfabricated using pre-annealing. However, because of lack of fusion of wrapped aroundgrains, grain density of surface can be further imporved.In summary, through a large number of comparative experiments, we clearlystudied actual situation of evaporation of Cu, Sn and Zn raw materials, successfullyprepared CZTS and CZTSSe thin films, systematically analyzed key points ofpreparation of CZTSSe thin film by pre-annealing of metallic precursor, and carefullystudied effect and influence of pre-annealing for growth of thin film. The study abovegave important experimental data reference to vacuum physical method for fabricationof CZTSSe thin films.