本論文研究是以化學水浴沉積法（CBD）及真空濺鍍法製作CuInSe2（CIS）薄膜太陽能電池之緩衝層硫化鎘薄膜，化學水浴沉積法分為共溶法及分溶法：(1)共溶法為將秤量好之藥品-硫酸銨、硫酸鎘、硫脲與氨水、去離子水400 ml混合；(2)分溶法為將秤量好之硫酸銨、硫酸鎘分別溶於50 ml去離子水中，而硫脲與氨水混合，之後將三者混合於300 ml去離子水中，藉此合成最終溶液。
採用硫化鎘作為CIS薄膜太陽能電池之緩衝層，主要原因在於硫化鎘能在CIS（吸收層）與透明導電層間達到能階緩衝的目的。本實驗化學水浴沉積法在大氣環境進行；濺鍍法則在3.7 mtorr之真空環境進行。首先兩種製程方式分別先將硫化鎘薄膜成長於鈉玻璃(Soda-lime)基板上，經分析取得薄膜最佳製程參數後，在與CIS/Mo/Soda-lime進行堆疊，透過四點探針量測其p-n二極體特性。濺鍍法成長硫化鎘薄膜採用RF功率200 W~500W進行，經由分析較後發現，以RF功率500 W所成長之硫化鎘薄膜厚較為均勻，且薄膜厚度易於控制。而化學水浴沉積法成長硫化鎘薄膜使用上述兩種方法所產生的溶液，以時間（20 min~60 min）及溫度（70 ℃~85 ℃）為變數進行。經由分析比較後發現，分溶法在反應溫度80 ℃和時間60 min所成長之硫化鎘薄膜表面較為平整，且膜厚較為均勻。而分溶法（反應溫度80 ℃和時間60 min）與濺鍍法所得硫化鎘薄膜經光學特性分析發現，分溶法在入射光波長500 nm時的透光率為61%，較濺鍍法的56%有明顯的改善，且其能隙與理論值2.4 eV相近。之後將兩者分別堆疊於CIS/Mo/Soda-lime上。經由四點探針電性分析比較後發現，分溶法（反應溫度80 ℃和時間60 min）可量測出較好p-n二極體特性曲線，表示與CIS層間形成有效的p-n接面，確定由化學水浴沉積法的分溶法能成長出品質較好的硫化鎘薄膜，故確定本實驗以化學水浴沉積法的分溶法為較佳產生硫化鎘薄膜的方法。 In this thesis, the CdS buffer layer of CuInSe2 (CIS) thin film solar cell is fabricated by Chemial Bath Deposition （CBD）and Sputtering Deposition (SD) methods, respectively. And there are two kinds of CBD methods, they are Co-melting CBD method and Separate-melting CBD method, respectively. The Co-melting CBD solution is completed with ammonium sulfate, cadmium sulfate, thiourea and ammonia melting together into 400 ml deionized water. For the Separate-melting CBD solution, firstly ammonium sulfate and mole cadmium sulfate melting separately into 50 ml deionized water, respectively; and thiourea and ammonia are mixed together; then the above three solutions are poured into 300 ml deionized water to become the final solution.
The reason of adopting the CdS thin film as the buffer layer of CIS thin film solar cell is that the CdS can play as energy gap buffer and reduce the band-offset between CIS absorbing layer and the Transparent Conductive Oxide (TCO) layer. The CdS thin films are generated by above two kinds of CBD methods in situation of atmosphere. And the CdS thin film generated by SD method is in situation of 3.7 mtorr vacuum pressure. In order to analyze the characteristics of the CdS thin films conveniently, the CdS thin films are firstly fabricated on Soda-lime, and the final found optimal CdS thin film is fabricated on the CIS/Mo/Soda-lime. Then the p-n diode characteristic of the CdS/CIS/Mo/Soda-lime is measured by four-point probe.
The CdS thin film obtained by SD method is adopted RF power with range from 200 W to 500W. It is found by analysis that 500 W is the optimal RF power; more uniform thickness of CdS thin film can be obtained and its thickness is easier to control. And the CdS thin films are fabricated by the above two kinds of CBD methods through various combinations of time interval from 20 to 60 minutes and temperature range from 70 ℃ to 85 ℃. It is found that the 80 ℃ and 60 minutes is the optimal combination; the smoother surface and more uniform thickness of Separate-melting CBD CdS thin film can be obtained. And it is found from optical characteristic analysis that in situation of emitted light wave length 500nm, the transmittance of the Separate-melting CBD CdS thin film is 61%, and it is better than that of SD CdS thin film with 56%. Meanwhile, the band gap of Separate-melting CBD CdS thin film is close to theoretical value of 2.4 eV. Then the Separate-melting CBD and SD CdS thin films are stacked on the CuInSe2/Mo/Soda-lime, respectively. It is shown that the p-n diode characteristic curve of the Separate-melting CBD CdS/CIS/Mo/Soda-lime is better than that of the SD CdS/CIS/Mo/Soda-lime. Thus, it is proved that the Separate-melting CBD method can obtained a better CdS thin film.