Earth-Abundant Chalcogenide Cu2BaSn(S,Se)4 Thin Film Growth for Photovoltaic Absorber

Abstract

近年來，以銅鋅錫硫硒為吸收層的太陽能電池日漸蓬勃發展，其原因來自於它不使用稀有(例如: 銦)，以及有毒的元素(例如: 鎘) 作為其合成的材料，然而，陽離子的錯位，如銅與鋅的錯位，及相關的能隙拖尾現象限制了其太陽能電池效率的表現。由於鋇離子的離子半徑非常大且性質獨特，與鋇相關的缺陷活化能非常高，不易於生成，且生成的缺陷其為淺層，不會造成載子分離困難進而降低太陽能電池的效率，的銅鋇錫硫太陽能電池近年來被視為銅鋅錫硫硒的替代吸收層，且能帶約為2.0電子伏特的性質對於串聯式太陽能電池上電極應用更為合適。 對於室內光伏應用，理想的能隙範圍為1.9電子伏特，因此我們透過摻雜硒元素進去銅鋅錫硫的薄膜，降低其能隙，進而產生銅鋅錫硫硒新的吸收層。藉由調控硫和硒的比例，我們可以達到一可調能隙範圍1.89到2.05電子伏特之光伏吸收層，可應用於家用能源自主電子設備的光伏器件或作串聯太陽能電池之應用。 在此篇研究中，我們透過真空的方式去製備此銅鋅錫硫硒吸收層，藉由拉曼、光激發螢光頻譜，以及X-射線繞射分析去探討薄膜的品質與辨別相的結構，最後，得到一個可調控能隙極具有相當潛力的太陽能電池吸收層。

In recent years, Cu2ZnSn(S,Se)4 (CZTSSe) materials have shown significant progress, which avoids using rare(Indium) and/or toxic(Cadmium) metals in thin-film photovoltaic (PV) technology. However, cationic disorder (i.e., Cu/Zn) and associated band tailing limit the device performance. Due to the distinct coordination environment of the large Ba2+ cation, the formation energy of Ba-related defects is high, and most of the defects show shallow properties, Cu2BaSnS4 (CBTS) has been proposed as an alternative to CZTSSe with the bandgap of 2.05-2.10 eV, which is promising to be a top-cell absorber in tandem photovoltaic conversion devices. Consider the ideal bandgap for indoor application is 1.9 eV, we further incorporated selenium into CBTS film to reduce the bandgap then form the Cu2BaSn(S,Se)4 (CBTSSe). By tuning the S/Se ratio, the tunable bandgap of absorbers with the range from 1.89 eV to 2.05 eV was obtained. These novel absorbers can not only be used as photovoltaics for household-energy-autonomous electronics but also as a good candidate for tandem solar cells. In this work, we use the vacuum process to synthesis the CBTSSe absorber and use Raman, photoluminescence (PL) spectroscopies, and X-ray diffraction (XRD) measurement as the tool to understand the quality and the information of phase identification. Finally, got potential absorber layers with tunable bandgap.