非晶與微晶矽氧吸收層與摻雜層在薄膜太陽能電池之特性分析與最佳化

Abstract

本研究中使用射頻電漿輔助化學氣相沉積系統來沉積非晶及微晶矽氧吸收層與摻雜層，並應用於矽薄膜太陽能電池。為了有效利用太陽光譜中的各個波段，使用雙接面或多接面結構可以達到增加吸收的效果。非晶矽氧薄膜由於有較大的能隙，適合作為吸收層並應用於雙接面或多接面太陽能電池中來增強短波長的吸收。首先我們先研究非晶矽氧薄膜的特性及它在單接面太陽能電池中的性能，並得到最佳的轉換效率為 4.43%。接下來我們將非晶矽氧吸收層應用於非晶矽氧/非晶矽鍺雙接面太陽能電池。隨著非晶矽氧吸收層的厚度增加，短路電流密度隨之增加。本文中最高的雙接面太陽能電池效率為 7.38%。 此外，微晶矽氧薄膜有較大的能隙，較低的吸收係數及較高的電導，適合應用於摻雜層。然而氧的加入使得結晶率與電導同時下降。本研究中藉由調變製程參數，相較於非晶矽n型摻雜層，微晶矽氧n型摻雜層可以獲得較大的能隙、較低的折射率及較高的電導。上述特性使微晶矽氧n型摻雜層與透明導電層的特性相似，因此我們將非晶單接面太陽能中的非晶n型摻雜層及透明導電層之背反射結構用微晶矽氧n型摻雜層代換，本文中最佳的非晶矽單接面太陽能電池開路電壓為 900 mV，短路電流密度為 15.17 mA/cm2，填充因子為72.7%及轉換效率為 9.92%。

In this study, plasma-enhanced chemical vapor deposition (PECVD) was used to deposit hydrogenated amorphous (a-SiOx:H) and microcrystalline (μc-SiOx:H) silicon oxide for thin-film solar cell applications. In order to effectively enhance the broaden spectral response, tandem or multi-junction structure was employed. The wider bandgap amorphous silicon oxide (a-SiOx:H) was a suitable absorber for the top cell. In this thesis, we first studied the characteristics of a-SiOx:H thin-films and the performance of a-SiOx:H single-junction solar cells. The optimized efficiency was 4.43%. Then we used a-SiOx:H absorber as the top cell in an a-SiOx:H/a-SiGe:H tandem solar cell. The Jsc increased and F.F. decreased with increasing in the thickness of top cell. The highest efficiency of a-SiOx:H/a-SiGe:H tandem solar cell was 7.38%. Moreover, the μc-SiOx:H with wider bandgap, lower absorption coefficient and higher conductivity was a suitable doped layers. However, the incorporation of oxygen decreased the crystalline fraction as well as the conductivity. In this study, by optimizing the deposition conditions, the μc-SiOx:H film with the higher bandgap, higher conductivity and lower refractive index than that of a-Si:H was obtained. The characteristics of μc-SiOx:H n-layer was found to be similar to transparent conductive oxide (TCO). Thus, we replaced the a-Si:H(n)/TCO back reflector by μc-SiOx:H(n) in a-Si:H single-junction solar cell. The highest efficiency of the a-Si:H single-junction solar cell was 9.92% with Voc = 900 mV, Jsc = 15.17 mA/cm2 and F.F. = 72.7%.