以疊層濺鍍法製備銅鋅錫硫薄膜太陽能電池光吸收層之研究

Abstract

本研究以濺鍍法鍍製Cu2S、ZnS與SnS2等前驅物（Precursor）疊層結構，再施予硫化退火以製成Cu2ZnSnS4（CZTS）薄膜做為薄膜太陽能電池（Thin-film Solar Cells）之光吸收層，討論前驅物疊層順序、硫化退火溫度、退火時間與SnS2厚度對CZTS薄膜微觀結構與成分組成的影響。 不同疊層順序之前驅物經硫化退火處理，掃描式電子顯微鏡（Field Emission Scanning Electron Microscopy，SEM）分析顯示僅ZnS/SnS2/Cu2S（4-ZTC）可形成單層CZTS薄膜，其它疊層則出現脫膜或不完全合金反應現象（如ZnS/Cu2S/SnS2（3-ZCT）），故4-ZTC為較佳之疊層順序；為增加結晶性並避免Sn的嚴重損失，570°C、60分鐘的退火為較佳的退火條件；改變SnS2厚度發現，適量的Sn含量可得較佳品質之CZTS薄膜，當SnS2厚度0.45微米時，X光繞射與Raman光譜分析顯示可形成單一相CZTS結構；SEM分析顯示CZTS薄膜之晶粒粒徑約1微米；能量散佈光譜儀分析顯示CZTS薄膜之化學劑量比約為Cu24.46Zn14.52Sn11.53S49.7，為貧銅/富鋅（Cu-poor/Zn-rich）之組成；紫外光-可見光光譜分析顯示光學能隙約為1.49 eV；霍爾效應分析顯示主要載子種類為p型，載子濃度為7.37x10^15 cm^-3及載子遷移率為4.47 cm^2V^-1sec^-1。

This study prepares the precursors comprised of Cu2S, ZnS and SnS2 stacking layers to form the Cu2ZnSnS4 (CZTS) photon absorption layer for thin-film solar cell via a sulfurization at 570°C. The influence of stacking-layer struture, sulfurization temperature and time duration as well as the thickness of SnS2 on the microstructure and composition of CZTS thin film was investigated. For the samples subjected to the sulfurization, the scanning electron microscopy found that the ZnS/SnS2/Cu2S (4-ZTC) may form single-layer CZTS thin film whereas the rest of stacking layer structures are inappropriate for CZTS formation due to the delamination from substarte or incomplete alloy reactions. The sulfurization at 570°C for 60 min was identified as the best heat-treatment condition since it provides good crystallinity and is able to avoid severe Sn loss in CZTS layer. As to the influence of thickness of SnS2, x-ray diffraction and Raman spectroscopy analyses found that single-phase CZTS with the grain size of 1 micro meter may form in the 4-ZTC stacking layer containing 0.45-micro meter thick SnS2. Energy dispersive spectroscopy revealed the composition of such a CZTS film is Cu-poor/Zn-rich with the stoichiometry of Cu24.46Zn14.52Sn11.53S49.7. UV-visible spectroscopy indicated the bandgap of CZTS film is 1.49 eV. Hall effect measurement found that the CZTS layer is a p-type semiconductor with major carrier concentration of 7.37x10^15 cm^-3 and carrier mobility of 4.47 cm2V^-1sec^-1.