Preparation And Photoelectric Properties Of Highly Efficient Cu₂ZnSn?S,Se?₄?CZTSSe? Thin Film Solar Cells

Kesterite Cu2ZnSn?S,Se?4?CZTSSe?has attracted much more attention as a promising substitute for CIGS solar cells on account of its outstanding optoelectronic properties and earth abundant,as well as nontoxic.The CZTSSe material is derived from a Cu?In,Ga?Se2?CIGS?material,and the precious elements In and Ga in CIGS are replaced with relatively inexpensive Zn and Sn to obtain a CZTSSe material having similar properties.Up to now,CZTSSe's solar cells efficiency has reached 12.6%,but it still has a certain gap with CIGS's 22.6%efficiency,and less than its theoretical value of 31%.Many studies have shown that there are two main factors affecting the efficiency of CZTSSe thin film solar cells.One is the crystal quality of the CZTSSe absorber layer.The method that how to prepare solar cells with high quality film quality needs to be explored;the other is how to collect more efficiently.Photogenerated carriers are used to increase battery performance and increase parameters such as open circuit voltage,short circuit current,fill factor,and efficiency.The generally structured CZTSSe solar cell has a multi-layer structure,causing the interface at the contact thereof to generate a fractured chemical bond,forming an interface state,which causes photogenerated carriers to easily recombine in these unstable regions,thereby reducing the output of electrons to the outside.In addition,during the growth of CZTSSe and the electrode preparation process,some grain boundaries and defects are also generated,which also negatively affects the collection of carriers.In order to solve this problem,it is necessary to add a passivation layer between the films to suppress recombination.The passivation layer can compensate for the chemical bonds of the dangling to reduce the density of the defect states,and can also generate a fixed charge to reduce the surface recombination rate.The main research contents of this paper are:?1?The CZTS prefabricated film was successfully prepared by metal salt thiourea method,and the CZTSSe film was prepared by selenization at 550°C.The results showed that the crystal structure and crystal quality of the CZTSSe film after selenization were better than those of the CZTSSe film.The unselenized film has good single-phase and crystallinity.The thickness of the CZTSSe film after selenization is about 1?m,the optical band gap is about 1.07 eV,and its Cu/?Zn+Sn?=0.81,S/?S+Se?=0.12.?2?The band gap of CZTSSe is about 1.0-1.5 eV,which has good band matching characteristics with Si materials.In this paper,single crystal Si is used as a heteroepitaxial growth substrate of CZTSSe to prepare solar devices,and in CZTSSe and Si The passivation buffer layer Al2O3 was added to study the influence of different thickness of Al2O3 film on the photoelectric properties of the device,and the optimal preparation conditions of CZTSSe film were given.?3?In order to further study the influence of passivation layer on CZTSSe solar cells and improve the efficiency of photovoltaic devices,we use soda-lime glass?SLG?as the sinking bottom,by depositing Al2O3 films of different thicknesses,and preparing SLG/Mo/The photovoltaic device with CZTSSe/Al₂O₃/CdS/ZnO structure systematically studied the influence of the thickness variation of Al2O3 layer on the structure and photoelectric characteristics of the device.We found that the V_oc,J_sc and?of the CZTSSe solar cell deposited with the 2 nm Al₂O₃ film had the highest values of 0.361 V,33.78 mA/cm² and 5.66%,respectively.The improvement of device performance is attributed to the fact that the Al₂O₃passivation layer can not only produce chemical passivation effect,but also make H ions can effectively compensate the dangling bonds between interfaces.The O ions in the Al₂O₃ film can also generate field passivation to suppress carrier recombination.