銅鋅錫硫(Cu2ZnSn(S,Se)4)薄膜作為太陽能電池吸收層材料因其較其他商用太陽能電池低廉的製造成本而極具發展潛力。目前銅鋅錫硫太陽能電池最高效率為美國IBM團隊的12.6％，仍不比由德國ZSW團隊提出之具有相似結構的銅銦鎵錫太陽能電池的21.7％。銅鋅錫硫太陽能電池主要的問題為較低的開路電壓(Voc)，已有廣泛的研究指出銅鋅的無序排列與硫硒的不均勻分布造成之能帶擾動會降低銅鋅錫硫太陽能電池的開路電壓，此外，諸如較低的介電係數、大量的缺陷、鈍化不完全的晶界等皆會使銅鋅錫硫太陽能電池的開路電壓降低。
本研究旨在利用氟化鎂鈍化技術，在不需做後續回火處理的情況下鈍化銅鋅錫硫吸收層表面的晶界，藉由掃描式表面電位顯微鏡(Scanning Kelvin Probe Microscopy)分析可知，經過氟化鎂鈍化技術處理的銅鋅錫硫材料之表面電位由18.2mV上升至32.78mV，而晶界上較強的負電位形成之電場鈍化可進而減少電子電洞對之復合現象(electron-hole recombination)。導納頻譜分析(Admittance Spectroscopy)結果指出缺陷能量由220meV減至133meV，此結果可能為介面上氟化鎂產生的電場鈍化效應減少電子電洞對之復合所致，此效應亦可由氟化鎂處理後之太陽能電池較長的載子生命週期(carrier lifetime)印證。透過氟化鎂鈍化技術，本研究可同時使短路電流密度(Jsc)由 30.71 mA/cm2 提升至32.61 mA/cm2、開路電壓由0.44 V提升至0.46 V，最後將銅鋅錫硫太陽能電池之效率提升至9.36%。

Thin film solar cells, based on Cu2ZnSn(S, Se)4 have attracted widespread interest, due to its high potential for a lower production cost than commercial solar cells. However, highest efficiency for the CZTSSe solar cell has only achieved 12.6% from IBM group in the USA and this is still lower than CIGS solar cell’s 21.7 % from ZSW (Zentrum für Sonnenenergie - und Wasserstoff-Forschung - or Center for Solar Energy and Hydrogen Research - Baden-Württemberg) group in Germany with similar structure. One of the critical issues in CZTSSe solar cells is Voc (open-circuit voltage) deficit. The Voc deficit in the CZTSSe solar cell due to Cu/Zn disorders and band gap fluctuation from non-uniform S/Se distribution have been investigated. In addition, several factors including low dielectric constant, large populations of defects, and un-passivated grain boundaries are issues that limit the Voc of CZTSSe solar cell.
In this thesis, we enhance the Voc of CZTSSe solar cell without post-annealing treatments by inserting an alkaline earth fluoride (MgF2) to passivate grain boundaries (GBs) of CZTSSe surface. Direct and indirect effects of MgF2 at grain boundaries and near-interface region in the CZTSSe surface has been investigated in this study. We found that the electronic properties of the GBs are enhanced by MgF2 without post-annealing treatments. According to the scanning Kelvin probe microscopy results, the potential of the sample with MgF2 increases from 18.2 mV to 32.78 mV. This effect leads to a higher negative charge at GBs and forms an electric field passivation, reducing the electron-hole recombination. The results of admittance spectroscopy show that the defect energy level decreases from 220 meV to 133 meV, which is possibly caused by the electric field passivation from the MgF2 at the interface and reduction of the electron-hole recombination. Such mechanism can be also supported by a longer carrier lifetime for the sample with MgF2 (30.6 ns) than pristine sample (20.3 ns). As a consequence, the current density (Jsc) and open circuit voltage (Voc) can be both improved from 30.71 mA/cm2 to 32.61 mA/cm2 and 0.44 V to 0.46 V, respectively. Finally, a CZTSSe solar cell with 9.36 % efficiency was achieved by using 10nm MgF2 without post-annealing treatments.

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