三元共电沉积法制备Cu_2ZnSnS_4薄膜

Co-electrodeposition of CZT precursor for Cu_2ZnSnS_4 thin film absorber layer

利用三元共电沉积制备金属前驱体,经预加热和硫化热处理后,成功合成了Cu_2ZnSnS_4薄膜。借助循环伏安法确定三元共沉积电位为E=-1.25V,考察pH值和电解液离子浓度对金属前驱体元素成分和物相的影响,筛选出电沉积的最佳工艺参数(8mmol/L SnSO_4,22mmol/L CuSO_4·5H_2O,22mmol/L ZnSO_4·7H_2O,200mmol/LNa_3C_6H_5O_7·2H_2O和pH值=5.7),沉积到成分比例接近最佳元素比的金属前驱体(n(Cu)/n(Zn+Sn)≈0.8,n(Zn)/n(Sn)≈1.2)。经300℃预加热后,金属前驱体转变成以Cu_5Zn_8和Cu_6Sn_5二元合金为主的金属固溶体,为后续硫化热处理形成纯相的CZTS奠定了基础。硫化过程中,硫化时间和硫化温度对薄膜结构形貌的影响显著。随着硫化时间的增大,CZTS的特征峰的强度增大,杂相衍射峰(Cu_(2-x)S、SnS和Cu_2SnS_3)的强度减弱,CZTS逐渐纯化。硫化时间为60min时,薄膜具有良好结构和形貌,而进一步硫化,易促使薄膜分解。过低的硫化温度会导致薄膜产生较多的二元和三元杂相,而硫化温度过高则会产生Sn和Zn的挥发流失。580℃时,CZTS薄膜的晶粒轮廓分明、晶界清晰、分布致密均匀,薄膜厚度约为2μm,与Mo层的接触紧密,无间隙,附着性增强。

In this study,co-electrodeposition was used to fabricate CuZnSn precursor,and followed by preheating and sulfurization to synthesize Cu2ZnSnS4absorber layer.The co-deposition potential E=-1.25V was determined by cyclic voltammetry（CV）.The effects of pH and electrolyte concentration on the composition and phases of the metal precursor were investigated.By optimization of the parameters,a CZT film with composition close to n（Cu）/n（Zn＋Sn）≈0.8,n（Zn）/n（Sn）≈1.2 was deposited from an aqueous solution containing8mmol/L SnSO4,22mmol/L CuSO4·5H2O,22 mmol/L ZnSO4·7H2O,and 200 mmol/L Na3C6H5O7·2H2O with pH=5.7.After preheating at 300℃,the metal precursor transformed into a solid solution of Cu5Zn8and Cu6Sn5alloys,which established the foundation for a pure CZTS formation.During sulfurization,annealing time and temperature had a significant impact on the structure and morphology of the film.With the increase in annealing time,the intensity of the characteristic peak of CZTS increased,the intensity of impurity phase peaks（Cu（2-x）S,SnS and Cu2SnS3）decreased,and CZTS was purified gradually.When the sulfurization time was up to 60min,the film had a good structure and morphology,but the film was easy to decompose with longer annealing.Too low sulfurization temperature would lead to binary and ternary phases in the film,while too high temperature would result in the loss of Sn and Zn.When sulfurization temperature was 580℃,the CZTS film had obvious grain profile and distinct grain boundaries,and was dense and uniform（around 2μm thickness）with less voids and good adhesion to the Mo layer.