Fabrication Of Cu₂ZnSnS₄Thin Film Solar Cells Via Sol-gel Route

The Cu2ZnSnS4(CZTS) based solar cell are considered to be one of the mostpromising novel materials for thin film solar cells due to the free of scarce and toxicelements and the reduced cost for mass production. It is well known that CZTS hascommonly a kesterite structure and a suitable optical band gap of about1.50eV with alarge absorption coefficient (>104cm-1). So it is very suitable for solar cells.Nowadays, there are many preparation methods about CZTS thin film and solar cells,and have got high photoelectric conversion efficiency. This thesis adopted sol-gelmethod that was low cost, high output and low toxicity to prepare CZTS thin film andsolar cells. Detailed innovative research contents are shown as follows:1) The revolution of glue machine was related to the thickness and evenness ofCZTS films. The results showed that the greater the glue machine revolutions, thesmaller the thickness of the film. But the surface of the film was more homogeneous.Integrated two aspects,3000rpm was the best revolution. Meanwhile，the content ofthiourea in the solution was related to the crystal structure of CZTS thin films.Theresults showed that the molar ratio of S/(Cu+Zn+Sn)=2.5was the best preparationproportion.2) Post-processing played a crucial role on the performance of the CZTS film. Inthe experiment of annealing, the performance of525oC annealing samples was best,optical band gap was1.49eV, dark conductivity was0.909S/cm. When thetemperature was too high, so the nature of the film had generated Cu2-xSimpurity.After sulfuration, although the surface morphology was poor, but thecrystallization of the thin film was better than annealing. After sulfurized at550oC,the film was pure, without impurities, the conductivity was1.48S/cm and the opticalband gap was1.49eV.3) Ratios of each material in the solution was related to the content of eachsubstance in eventual samples. In the orthogonal experiments, we found that theZn/Sn=1.2ratio was better than others, such as crystallization, photoelectric properties and so on. Cu-poor greatly improved the properties of film. The ratio ofZn/Sn=1.2, Cu/(Zn+Sn)=0.90was best in the experiment.4) The CZTS thin-film battery of Glass/Mo/CZTS/CdS/ITO/Al structure wasprepared. Its efficiency was0.10%(open circuit voltage Vocwas142mV, currentdensity Jscwas2.2mA/cm2, the fill factor FF was32.54%). Although it had made theefficiency, but high series resistance, small parallel resistance leaded to lowefficiency. CZTS and CdS film were prepared by the method of antivacuum, it waseasy to appear the hole and cause the p-n junction short out. It made the parallelresistance too small. Due to the conductivity of the two layers films were not good, soseries resistance was too large.And the the interface processing was not perfect.Thesewere the reasons for the low efficiency.