摘要
本研究利用射頻電漿輔助化學氣相沉積(Radio-frequency plasma enhanced chemical vapor deposition, RF-PECVD)製備本質與磷化氫摻雜氫化非晶矽(a-Si:H)薄膜堆疊結構，射頻電漿輔助化學氣相沉積為產業廣泛使用之設備，學理發展完整、設備技術純熟，其特性為沉積速率較緩慢；能沉積高緻密性薄膜，故適合應用於嚴格要求低薄膜厚度與高薄膜品質之異質接面太陽能電池(Heterojunction with intrinsic thin layer solar cell, HIT)的結構中。本實驗以RF-PECVD引入矽甲烷(SiH4)、氫氣(H2)、磷化氫(PH3)與氬氣(Ar)製備本質堆疊磷摻雜氫化非晶矽薄膜，實驗規劃調變射頻功率(RF power)、氫稀釋比例(Hydrogen dilution ratio)、基板溫度(Substrate temperature)、電極間距(Electrode distance)、製程壓力(Pressure)、磷化氫氣體流量(PH3 Flow)等製程參數對a-Si:H薄膜特性影響，並且使用四點探針薄膜電阻量測儀(Four point sheet resistance meter) 、霍爾效應分析儀(Hall)、橢圓偏光儀(Ellipsometer)、二次離子質譜儀(Secondary ion mass spectrometer, SIMS)量測薄膜結構與電特性、穿透式電子顯微鏡(Transmission electron microscopy, TEM)觀察薄膜接面平滑度與鈍化品質之關係，最後以光電導生命週期量測儀 (Photoconductance lifetime tester)測量少數載子生命週期(Lifetime)與表面載子複合速率(SRV)結果得知鈍化品質優劣。未來期望應用於異質接面太陽能電池背表面電場上，以提升電池開路電壓與短路電流。 研究結果顯示，在調變參數的情形下，薄膜結晶率愈高則導電特性愈好，而磷摻雜氫化非晶矽薄膜中的磷原子雖然可以貢獻電子提升薄膜電特性，但是過多的磷原子相對會導致缺陷密度提升，不但不利於摻雜的活化更嚴重影響少數載子生命週期，故如何再生命週期與導電特性上取得平衡是相當重要的關鍵。 進行優化後的堆疊結構中不但提升本質層之鈍化效果，更能在太陽能電池池內建構一背電場提升短路電流，製備出之薄膜之摻雜濃度可大於1019且少數載子生命週期可大幅提高到1.8 msec以上。
並列摘要
In this study, the intrinsic/phosphorus doping hydrogenated amorphous silicon (a-Si:H) double structure was optimized by the process conditions in which film growth of doped silicon as a back surface field (BSF) layer in a symmetric cell structure was prepared by standard radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). PF-PECVD had major advantages: (1) low operation temperature, (2) higher compactness of deposited layer, (3) good passivation properties of deposited layer, (4) good step coverage. The process parameters effect of a-Si:H thin films such as radio-frequency power, hydrogen dilution ratio, substrate temperature, electrode distance, pressure, PH3 flow was investigated. The thin films physical and optical properties were analyzed by Four Point Sheet Resistance Meter, Hall, TEM, Ellipsometer, Photoconductance lifetime tester and Secondary Ion Mass Spectrometer. We determined the thin film quality by photo conductance lifetime tester. In addition, this double structural film will be applied to heterojunction with intrinsic thin layer (HIT) solar cells as a back surface field layer to improve the open-circuit voltage and short-circuit current of solar cells. The results of experiments show that the excess phosphorus atoms in the films will increase the defect and degrade the electronic properties. Thus, the control of phosphorus content in the films is very important to obtain a high electronic properties. We achieved high quality of BSF on surface passivation, resulting lifetime up to 1.5ms and concentrations > 1019 in 4cm2 HIT solar cell.
參考文獻
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