本研究主要是利用氧化鎵鋅(ZnO:Ga)作為透明導電層之接觸電極材料，並且應用於矽薄膜太陽能電池元件。氧化鎵鋅薄膜普遍使用物理氣相沉積之濺鍍方式成長，而利用濺鍍製程參數控制薄膜品質及特性值得我們進一步的研究。在論文中，首先將探討氧化鎵鋅材料應用於微晶矽薄膜太陽能電池，作為前後之透明接觸電極層並分析元件效率的影響。
此外，我們進一步研究將表面粗糙化的氧化鎵鋅薄膜作為薄膜太陽能電池之背電極接觸層。氧化鎵鋅薄膜沉積於元件吸收層上，利用電漿乾式蝕刻與化學濕式蝕刻兩種不同方式形成粗糙化之氧化鎵鋅透明電極層。氧化鎵鋅透明電極層在電漿乾式蝕刻後，可增加光學的擴散反射及反射霧度特性，並且比較電漿乾式蝕刻之粗糙化結構在非晶矽薄膜太陽能電池之特性，光電流以及影響因子可獲得改善，元件效率也相對增加了4.6%的幅度。
而在化學濕式蝕刻的部份，粗糙化之氧化鎵鋅背接觸電極應用於微晶矽薄膜太陽能電池。利用化學蝕刻氧化鎵鋅薄膜5-6秒的製程，可獲得較佳的薄膜擴散反射特性，在最佳蝕刻條件下，粗糙化之氧化鎵鋅背接觸電極可得到6.88%微晶矽太陽能電池之效率 (FF = 68 %, VOC = 471 mV and JSC = 21.48 mA/cm2)。微晶矽太陽能電池效率從6.54 %提升到6.88%，主要是由於粗糙化之背反射層增加了反射光路徑，進而提升元件吸收效率使元件光電流增加，而從外部量子效率分析也可發現主要是長波長光譜響應的部分獲得改善。
化學濕式蝕刻之粗糙化背反射層的光捕捉效應(light trapping effect)也在疊層式薄膜太陽能電池中得到驗證，粗糙化背反射層應用於疊層式薄膜太陽能電池中，由於改善了光捕捉效應，所以增加了底部電池(bottom cell)相對8%的短路電流值。研究結果說明長波長光捕捉效應之改善，主要是歸因於粗糙化的氧化鎵鋅背反射層增加了元件光捕捉能力，並提高2 μm底電池之疊層式薄膜太陽能電池效率。

Gallium-doped zinc oxide (ZnO:Ga, GZO) thin films are of interest to the semiconductor industry as transparent conductive surfaces and as transparent contact electrode layers for applications such as silicon thin film solar cells. Physical vapor deposition (PVD) via sputtering is commonly used to produce thin films such as GZO, but film quality and characteristics depend significantly on the PVD processing parameters. Additionally, the effects of the produced GZO material when applied as multi-layer front and back layer electrodes to hydrogenated microcrystalline silicon (μc-Si:H) thin film solar cells is evaluated in terms of open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF) and efficiency (Eff.) of the cells.
Besides, our study considers texturing of GZO films used as back contacts in silicon thin film solar cells. GZO thin films are first prepared by conventional methods. The propertied of as-deposited GZO surface back contact are modified so that light trapping on silicon thin film solar cell is enhanced. Texturing is performed by dry plasma etching in a CVD process chamber and chemical wet etching process. Comparison of the with/without texturing GZO films shows that plasma etching increases optical scattering reflectance and reflection haze. SEM and TEM are used to evaluate the morphological treatment-induced changes in the films. Comparison of the amorphous silicon solar cells with/without texturing shows that the plasma treatment increases both the short-circuit current density and fill factor. Consequently, a-Si solar cell efficiency is relatively improved by 4.6 %.
Furthermore, surface wet etching is applied to the GZO back contact in μc-Si:H thin film solar cells. Texturing enhances reflective scattering, with etching around 5-6 seconds producing the best scattering, whereas etching around 5 seconds produces the best fabricated solar cells. Etching beyond these time produces suboptimal performance related to excessive erosion of the GZO. The best μc-Si:H solar cell achieves FF = 68 %, VOC = 471 mV and JSC = 21.48 mA/cm2 (Eff. = 6.88 %). Improvement is attributed to enhanced texture-induced scattering of light reflected back into the solar cell, increasing the efficiency of our lab-made single μc-Si:H solar cells from 6.54 % to 6.88 %. Improved external quantum efficiency is seen primarily in the longer wavelengths, i.e. 600 to 1100 nm. However, variation of the fabrication conditions offers opportunity for significant tuning of the optical absorption spectrum.
Effects of textured back reflectors on light trapping in a-Si / μc-Si:H tandem cells are investigated with textured GZO back contacts obtained by surface wet etching. It is observed that rough back reflectors in fabricated tandem solar cells increase the short circuit current density of the bottom cells by 8 %, which is attributed to light-trapping improvement. It is shown that enhanced longer wavelength light trapping is mainly attributable to improved light scattering at the back side by comparing identical a-Si / μc-Si:H tandem solar cells, both with a GZO back reflector but only one with a textured back reflector. Effectiveness of the textured GZO back reflector is also demonstrated in a textured a-Si / μc-Si:H tandem cell with a bottom cell thickness of 2 μm, which showed higher conversion efficiency than the reference cell.

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