Study On Absorption Layer Optimization And Device Performance Of Cu₂ZnSn?S,Se?₄ Film Solar Cells

Photovoltaic technology is an effective way to solve the energy crisis of human being.At present,developing the solar cells with eco-rich material resources,nontoxicity,and low-cost nature and high-efficiency is the research hotspot in the field of photovoltaics.Copper-zinc-tin-sulfide semiconductors have attracted a great deal of attention because of their characteristics of earth abundant resources,environmental friendliness,and excellent photovoltaic performance.To date,a certified-record photoelectric conversion efficiency of 12.6% has been obtained for Copper-zinc-tinsulfide thin-film solar cells,but there is still a large gap compared with the theoretical conversion efficiency(32%).There are many problems such as large interface defects,poor energy band-matching,and poor film quality of the absorption layer to limit the improvement of its efficiency.Especially,fabricating a high-quality absorption layer has become the biggest challenge in this field.Based on this research background,the effects of the element ratio in absorption layer and annealing temperature of precursor films on the quality of copper-zinc-tin-sulfur films have been systematically studied.After that,a higher device efficiency has been achieved,the main results are as follows:(1)By regulating the ratio of solute in 1,2-ethylenediamine and 1,2-ethanedithiol mixed solvent system to control the ratio of Cu/(Zn+Sn)and Zn/Sn inside copper-zinctin-sulfur films.Finally,in the case of Cu/(Zn+Sn)=0.74 and Zn/Sn=1.25,the photoelectric conversion efficiency of devices is optimal(7%-8%);(2)By adjusting the annealing temperature of the precursor films,the content of the carbon residue has been effectively controlled.It is found that the carbon content in the precursor films under the annealing temperature range of 350°C to 400°C is beneficial to the nucleation and maturation of copper-zinc-tin-sulfur crystals in the selenization process.Furthermore,the carrier and surface defect densities of selenized absorbers are also significantly suppressed by adjusting annealing temperatures,leading to the average PCE improved from 5.1% to 9.4%.The champion cell with PCE of 10.04% has been achieved under the optimal annealing temperature(380°C).