CIGS太陽能電池雙層鉬背電極之薄膜成長與特性分析

本文主要以脈衝直流磁控濺鍍系統製備CIGS太陽能電池之雙層鉬背電極，實驗主要利用田口實驗以L9(34)直交表採用電源功率、工作壓力、基板偏壓、基板溫度作為調控參數進行薄膜成長，並且透過FE-SEM觀察薄膜的表面及斷面型態及以膠帶測試法進行薄膜附著性測試。針對鍍膜速率、薄膜粗糙度、薄膜電阻率及薄膜反射率進行特性分析，最終以田口實驗法分析得到雙層鉬金屬薄膜之最佳化參數。為提升太陽能電池的電性傳導及太陽光子行走路徑，得到優良的電池轉換效率，因此經由田口實驗法進行特性之S/N比分析得到最佳化參數，針對四項特性的總合要求，依序為薄膜電阻率、薄膜反射率、薄膜粗糙度及鍍膜速率，以一半準則，得到本研究雙層鉬薄膜總合最佳化參數水準為電源功率270 W、工作壓力7 mTorr、基板偏壓+100 V 、基板溫度200 ℃，採用此製程參數可得到平衡四項特性最佳數據的結果。總合最佳化參數得到一擁有優良電阻率(4.63×10-5 Ω-cm)、反射率(70.61 %)及鍍膜速率(21.43 nm/min)的雙層鉬薄膜，此特性結果為變異較小且平衡各項特性的最佳化數值。在附著性測試分析得出基板溫度與功率水準提高，幫助晶粒生長提升結晶性以致通過附著性測試。而工作壓力越低以及功率與基板溫度提升，造成晶粒尺寸提升，其薄膜較為致密有較小的晶界及數量，得到優良電阻率。功率為影響薄膜反射率的重要參數，功率越高則反射率越好，但工作壓力越高及基板溫度提升造成反射率變差。基板偏壓為影響粗糙度之重要參數，施加基板偏壓可降低粗糙度，本研究中除少數試片粗糙度高於0.5 nm，其餘所有試片皆低於1 nm，顯示採用脈衝直流濺鍍系統製作雙層鉬薄膜，可得到優良的薄膜粗糙度品質。

關鍵字

脈衝直流電源；田口實驗法；鉬背電極；電阻率；反射率

並列摘要

This paper mainly described the Pulsed D.C. magnetron sputtering system preparation of bilayer Mo back contact of CIGS solar cells. The experiment utilize power, working pressure, bias voltage, substrate temperature as control parameters of Taguchi L9(34) orthogonal array for Films growth, in addition, through the FE-SEM to observe the film surface, cross-section and Films adhesion test by the tape test method, against coating rate, roughness, resistivity and reflectivity would carry out characteristics analysis. Ultimately, to obtain the optimization parameters of bilayer-molybdenum films by using Taguchi method. In order to enhance the electrical conductivity of the solar cells and solar photons walking paths, as a result of to obtain superior conversion efficiency for cells. Therefore, through S/N ratio analysis form the four above characteristics can obtain the optimized parameters via the Taguchi method. For the requirements to the sum of the four characteristics, according to the order of resistivity, reflectance, roughness and coating rate. Use the Half of the Criteria can be obtained bilayer molybdenum film ultimately of the optimized parameters which is Power 270 W, working pressure of 7 mTorr, bias voltage of +100 V, substrate temperature of 200 °C. The process parameters can be balanced the four characteristics of the best data. The ultimate optimization parameters have excellent resistivity (4.63×10-5 Ω-cm), reflectance (70.61 %), and the coating rate (21.43 nm/min) of the bilayer-molybdenum thin Films. In addition, the result of the variation is small and the balance of the characteristics optimum value. Through adhesion test analysis, it can be obtained the increasing of the substrate temperature and the power levels. Besides, the lower working pressure as well as the power and the substrate temperature which are elevated, it causing the grain size is increased, that makes the Films has higher density and small grain boundary as well as lower quantity. Thus, the Films have excellent resistivity. The important parameters of affecting the thin-film reflectance is the power, this shows that the higher the power, the better the reflectance. Moreover, the higher working pressure and the substrate temperature cause decrease reflectance. The important parameters of affecting roughness are bias voltage, therefore, increasing the bias voltage can reduce the roughness. In this study, except for the few specimens which roughness higher than 0.5 nm, and the rest of all specimens of roughness are less than 1 nm. This shows that, by using Pulsed D.C. sputtering system to produce the bilayer-molybdenum film can be obtained the superior roughness quality.