Fabrication And Research Of Al Doped Cu₂ZnSn（S,Se）₄ Thin Film Solar Cells

As the compound semiconductor copper-zinc-tin-sulphur-selenium（Cu₂ZnSn（S,Se）₄,CZTSSe）have the advantages of lower cost,abundant elemental reserves on earth and high absorption coefficient(10⁴～10⁵ cm^-1)as well as being environment-friendly,they are widely valued as a very promising absorber layer material for thin film solar cells with a theoretical limit efficiency of 32%.However,the presence of a large number of instrinsic deep energy level defects and defect clusters in CZTSSe leads to severe open circuit voltage loss,limiting the device’s efficiency.To solve the above problems,this paper adopts the solution method to dope aluminium（Al）in CZTSSe and CZTS absorber layer films to partially replace Sn elements and reduce the harmful defects in CZTSSe and CZTS thin film solar cells,while the introduction of Al can adjust the device band gap and improve the EQE performance of the devices.The main research and main results of this paper is as follows:（1）The effects of different sulfoselenization processes on the performance of CZTSSe films and their devices were investigated and the best sulfoselenization conditions for subsequent experiments were explored.The crystal phase properties,crystal morphology,J-V and EQE properties of CZTSSe thin films prepared by different sulfoselenization processes were studied.The results showed that CZTSSe thin films prepared by soft sulfoselenization at 280°for 10 minutes and annealing at580°for 15 minutes and demonstrated a power conversion efficiency of 7.29%.（2）The effects of Al doping with different contents（Al/（Al+Sn）=0%,4%,6%,8%）（molar ratio）on CZTSSe thin films and their device properties were investigated.Absorber layer films of(Cu₂ZnSn_1-xAl_x（S,Se）₄,CZTASSe)absorber layer films with different Al contents were prepared under the optimum sulfoselenization process and the corresponding complete devices were also prepared.The substitution of Al for Sn reduces the number of deep energy level defects associated with Sn,increases the energy band band gap,improves the open circuit voltage(V_oc)and short circuit current(J_sc)of the cells,but the fill factor（FF）decreases.Ultimately,CZTASSe thin film solar cells with an efficiency of 9.81%were achieved when the Al content is Al/（Al+Sn）=6%.（3）Cu₂ZnSn_1-xAl_xS₄（CZTAS）absorber layer films were prepared by vulcanization of prefabricated layer films doped with a certain amount of Al（Al/（Al+Sn）=6%）（molar ratio）.A certain amount of Al doping in the CZTS absorber layer film instead of Sn reduced the density of deep energy level defect states in the CZTS absorber layer film and further increased the energy band band gap of CZTS.As a result,V_ocincreased significantly by 55.3 e V,but Al doping presents a significant inhibitory effect on the crystal growth of the CZTS absorber layer film with small grain size and many large voids.In additon,the shunt resistance(R_sh)reduces and series resistance（R_s）increases,which results in a lower fill factor（FF）.Finally,CZTAS solr cells with an efficiency of 6.53%were obtained.