|Abstract: ||以CdS為緩衝層的銅鋅錫硫(Cu2ZnSnS4, 簡稱CZTS)太陽能電池的量子效率在短波長波段下降是因為硫化鎘緩衝層的光學吸收。為了要進一步地改善在短波長波段的短路電流(Jsc)，可以藉由其他寬能隙材料來取代硫化鎘層。作為一個寬能隙、無毒且低成本的材料，以化學水浴沉積製作的硫化鋅為最好的替代材料。一般來說，化學水浴沉積有許多優點，例如:低沉積溫度、低製造成本、大面積沉積且最重要的一點，氨水可以恢復CZTS表面的正電荷有助於形成更好的pn接面。 在這篇論文中，含氧、氫氧之硫化鋅薄膜是用zinc sulfate hepta-hydrate (ZnSO4•7H2O), thiourea (SC(NH2)2) and ammonium hydroxide (NH4OH)在低溫的去離子水中反應形成。我們優化了各反應物的濃度、pH值和反應溫度以得到適合銅鋅錫硫太陽能電池的硫化鋅緩衝層薄膜。然而，這種材料的能帶位置是可調變的，透過調整硫氧的比例，從各種濃度的pH值和硫尿濃度下得到。最後，我們成功的製造出更好表現的硫化鋅薄膜取代傳統硫化鎘薄膜的緩衝層。目前最好的硫化鋅緩衝層元件效率可達4.1%，足以媲美標準的硫化鎘為基礎的5.69%。從外部量子效率光譜也可以明顯看出更多的電流收集在短波長區域的增長。|
The quantum efficiency of a CdS-buffered Cu2ZnSnS4 (CZTS) solar cell drops at short wavelengths due to the optical absorption of the CdS layer. Further improvement in short circuit current (Jsc) at shorter wavelengths can be achieved by replacing CdS with other appropriate wider band gap buffer materials. Being a wide bandgap material, non-toxic in nature, low-cost and high material abundance, CBD grown ZnS is one of the promising candidates for alternative buffer layers. Normally, in device fabrication the CBD method has many advantages, such as low deposition temperature, low-cost fabrication process, and easy to scale up for industrial fabrication. Besides, of most importance is the CBD method’s usage of ammonia solution enabling restoration of the positive surface charge of CZTS for the effective p-n junction formation. In this thesis, Zn(S,O,OH) thin film were synthetized by using zinc sulfate hepta-hydrate (ZnSO4•7H2O), thiourea (SC(NH2)2) and ammonium hydroxide (NH4OH) solution in DI water at relatively low temperature. We have optimized the concentrations of respective reactants concentrations, pH value and reaction temperature to obtain Zn(S,O,OH) thin film as a good buffer layer for CZTS. The band gap, and the band positions of this material are tunable by varying S/O ratios, resulting from various concentrations of thiourea and pH values. The elemental compositions, optical properties and coexisting multiple phases in the films have been investigated sequentially. Finally, we have used successfully prepared the Zn(S,O,OH) film in the final solar cell with a better performance to replace the conventional CdS buffer layer. The champion cell has achieved 4.1% in efficiency, which is comparable to the 5.69% efficiency of the standard CdS-based. The external quantum efficiency (EQE) spectra of our solar cell also evidenced the enhancement of carrier collections at short wavelengths.