本研究旨在利用UV浸潤的後處理方法對CIGS太陽能模組電池轉換效率的作用、最佳化以及機制進行探討。實驗上，我們利用市面的太陽能模組製作出了小電池和MTLM等結構；並在UV浸潤前後量測電池的光電流-電壓曲線，代入2-Diode公式進行電性參數擬合。實驗結果顯示浸潤效應主要在於提升電池的填充因子FF。此外，串聯電阻RS的下降顯示其為FF提升的主要原因。
進一步我們藉由MTLM量測結果來分析CIGS模組電池中的TCO(BZO，氧化鋅摻雜硼)的片電阻，及P2接面電阻在UV浸潤前後的變化。實驗結果顯示TCO占整體電池的串聯電阻的一半以上，且在UV浸潤後因其電阻下降導致了FF的提升。而UV浸潤的效果約在進行30分鐘後便接近飽和。我們還發現FF在UV浸潤後的提升不能穩定維持，會在UV浸潤後隨時間以指數型式衰退。此現象同樣在鍍有SiO2鈍化層的CIGS電池上，顯示造成FF衰退的原因可能來自材料內部，而非表面。
我們提出了一個假說，即假設所有與浸潤相關的效應皆來自TCO中的亞穩態帶電缺陷，來解釋上述現象。在未進行UV浸潤時，TCO的缺陷被電子填滿並帶負電，電子受到這些負電缺陷散射而有較低的載子遷移率。進行UV浸潤時，在n型半導體的TCO中產生的電洞被帶負電的缺陷捕獲，電荷中和減少了電子移動過程中的散射，載子遷移率因而提高，因此降低了電池的串聯電阻並提升FF。而此效益的衰退則來自電洞會隨著時間從缺陷被釋放，回到熱力學平衡的狀態。

This research mainly works on the effect, the optimization, and the mechanisms involved in the UV soaking post-treatment of CIGS solar module cells. Experimentally, various devices including small cells and MTLM structure were fabricated from the CIGS solar module. Light I-V curves before and after UV soaking were measured and fitted with a two-diode equation. The results have suggested that the soaking effect is mainly to improve the fill factor of the cell. Furthermore, the series resistance(RS) reduction was shown to be the main cause of the FF improvement.
TCO (boron doped ZnO, BZO) sheet resistance and P2 contact resistance of CIGS module were then derived from the MTLM measurements before and after soaking. The result showed that TCO takes place more than 50% of the total resistance, and it can be reduced by UV soaking, which effectively raised the FF. The soaking effect tends to saturate after 30 minutes of treatment. The FF enhancement was found not stable, it tends to decay exponentially with time after the soaking. Such an aging effect also observed on the SiO2 surface passivated CIGS cell, suggesting the cause may have resulted from the bulk, instead of the surface.
A hypothesis is proposed to explain all the phenomena. It assumes all the effects may have resulted from the metastable electronic defects of TCO. Without UV soaking these defects are filled with electrons and being charged negatively. This results in low electron mobility due to the large scattering cross-section of the charged defects. With UV illumination, holes of n-TCO are generated and being captured by the negatively charged defects. The neutralization reduces the series resistance and increases the FF of the cell. Such an enhancement decays with time eventually as holes are released from the metastable defects to attain the thermodynamic equilibrium.

1. Lee, T.D. and A.U. Ebong, A review of thin film solar cell technologies and challenges. Renewable and Sustainable Energy Reviews, 2017. 70: p. 1286-1297.
2. Green, M.A., et al., Solar cell efficiency tables (version 56). Progress in Photovoltaics: Research and Applications, 2020. 28(NREL/JA-5900-77544).
3. Neamen, D.A., Semiconductor physics and devices: basic principles. 2012: New York, NY: McGraw-Hill.
4. Tao, Y., Screen‐Printed Front Junction n‐Type Silicon Solar Cells. 2016. p. 47-73.
5. Snaith, H.J., The perils of solar cell efficiency measurements. Nature Photonics, 2012. 6(6): p. 337-340.
6. Ramanujam, J. and U.P. Singh, Copper indium gallium selenide based solar cells - a review. Energy & Environmental Science, 2017. 10(6): p. 1306-1319.
7. Chantana, J., et al., Influences of Fe and absorber thickness on photovoltaic performances of flexible Cu (In, Ga) Se2 solar cell on stainless steel substrate. Solar Energy, 2018. 173: p. 126-131.
8. Ong, K.H., et al., Review on substrate and molybdenum back contact in CIGS thin film solar cell. International Journal of Photoenergy, 2018. 2018.
9. Scofield, J.H., et al., Sputtered molybdenum bilayer back contact for copper indium diselenide-based polycrystalline thin-film solar cells. Thin solid films, 1995. 260(1): p. 26-31.
10. Wang, Y.-C. and H.-P.D. Shieh, Double-graded bandgap in Cu (In, Ga) Se2 thin film solar cells by low toxicity selenization process. Applied Physics Letters, 2014. 105(7): p. 073901.
11. Singh, U.P. and S.P. Patra, Progress in polycrystalline thin-film Cu (In, Ga) solar cells. International Journal of Photoenergy, 2010. 2010.
12. Pan, J., et al. Investigation of aluminum induced degradation in sputtered Al: ZnO for CIGS solar cells applications. in 2009 34th IEEE Photovoltaic Specialists Conference (PVSC). 2009. IEEE.
13. Shafarman, W., CIGS Module Design and Manufacturing. Photovoltaic Solar Energy, 2017: p. 204.
14. Shannan, N.M.A.A., N.Z. Yahaya, and B. Singh. Single-diode model and two-diode model of PV modules: A comparison. in 2013 IEEE International Conference on Control System, Computing and Engineering. 2013. IEEE.
15. 周哲寬, CuGa和In雙靶共濺鍍前驅層後硒化法製作銅銦鎵硒太陽能電池吸收層之研究與太陽能電池的擬合和模擬程式之製作, in 材料科學工程學系. 2019, 國立清華大學: 新竹市. p. 109.
16. Schroder, D.K., Semiconductor Material and Device Characterization. 2006: John Wiley & Sons.
17. Philips’Gloeilampenfabrieken, O., A method of measuring specific resistivity and Hall effect of discs of arbitrary shape. Philips Res. Rep, 1958. 13(1): p. 1-9.
18. Gostein, M. and L. Dunn. Light soaking effects on photovoltaic modules: Overview and literature review. in 2011 37th IEEE Photovoltaic Specialists Conference. 2011. IEEE.
19. Chantana, J., et al., Enhancement of photovoltaic performances of Cu (In, Ga)(S, Se) 2 solar cell through combination of heat‐light soaking and light soaking processes. Progress in Photovoltaics: Research and Applications, 2018. 26(10): p. 868-876.
20. Yu, H.-J., et al., Light-soaking effects and capacitance profiling in Cu (In, Ga) Se 2 thin-film solar cells with chemical-bath-deposited ZnS buffer layers. Physical Chemistry Chemical Physics, 2016. 18(48): p. 33211-33217.
21. Yoon, J.-H., et al., Characterization of efficiency-limiting resistance losses in monolithically integrated Cu (In, Ga) Se 2 solar modules. Scientific reports, 2015. 5(1): p. 1-9.
22. 李昱德, 銅銦鎵硒太陽能模組電池之串聯電阻量測方法設計與分析應用, in 材料科學工程學系. 2020, 國立清華大學: 新竹市. p. 74.
23. 蔡尚宏, 銅銦鎵硒太陽能電池模組之串聯電阻量測與分析, in 材料科學工程學系. 2019, 國立清華大學: 新竹市. p. 77.
24. Takahashi, Y., et al., Photoconductivity of ultrathin zinc oxide films. Japanese Journal of Applied Physics, 1994. 33(12R): p. 6611.
25. Bhatt, V., et al., Persistent photoconductivity in Al-doped ZnO photoconductors under air, nitrogen and oxygen ambiance: Role of oxygen vacancies induced DX centers. Ceramics International, 2019. 45(7): p. 8561-8570.
26. Al-Hilli, S. and M. Willander, The pH response and sensing mechanism of n-type ZnO/electrolyte interfaces. Sensors, 2009. 9(9): p. 7445-7480.
27. Peng, Y.-C., et al., First-principles calculations of electronic structure and optical properties of Boron-doped ZnO with intrinsic defects. Optical Materials, 2015. 39: p. 34-39.
28. Janotti, A. and C.G. Van de Walle, Native point defects in ZnO. Physical Review B, 2007. 76(16): p. 165202.
29. Schmidt-Mende, L. and J.L. MacManus-Driscoll, ZnO–nanostructures, defects, and devices. Materials today, 2007. 10(5): p. 40-48.
30. Thio, T., et al., DX centers in II-VI semiconductors and heterojunctions. Journal of electronic materials, 1996. 25(2): p. 229-233.