| 摘要: | 本研究利用電漿輔助化學氣相沉積(Plasma enhanced chemical vapor deposition,PECVD) 製備異質接面太陽能電池表面鈍化超薄氫化非晶矽薄膜，利用 PECVD 具有穩定沉積速率、良好的覆蓋均勻性、低溫成長易與其他製程整合之特點。本實驗調變射頻功率、氫稀釋比例、基板溫度等製程參數探討對a-Si:H 薄膜鈍化特性影響。先以橢圓偏光儀來量測及分析薄膜的結構特性，再以少數載子生命週期來判斷薄膜鈍化品質好壞，以及有效提升電池開路電壓(Voc)並提升異質接面太陽能電池整體效率。
研究結果顯示，在50nm氫化非晶矽薄膜中，綜合所有製程參數並於少數載子生命週期(Lifetime)得知薄膜皆呈現良好鈍化品質，但是經過退火過程反而使內部Si-H鍵結成為亂序，造成鈍化品質下降。另一方面在超薄5nm氫化非晶矽薄膜中，藉由退火前後少數載子生命週期結果得知，薄膜結晶率對於表面產生的缺陷，可經由熱退火過程改善缺陷比例，增加在基板接面中的Si-H鍵將補償表面的懸掛鍵，降低薄膜中復合中心的產生進而提升少數載子生命週期，證明好的鈍化品質發生在非晶轉微晶的過渡區。我們可成功於H2/SiH4=4、射頻功率20W、基板溫140 ℃條件下得到5nm 超薄氫化非晶矽薄膜最佳鈍化效果，並在熱退火條件300 ℃-120sec時，少數載子生命週期可達到1.2 msec； implied Voc提升至0.694 V；並使表面復合速率下降至10 cm/s。且在4吋FZ-N矽晶基板上carrier lifetime到達4.7msec、Implied Voc值0.725V，表面復合速率下降至2.98 cm/s。將此優化非晶矽鈍化薄膜實際應用於異質接面矽晶(CZ-n)太陽能電池，在電池面積1cm2時，在電池開路電壓Voc=0.66 V; Jsc = 36.71 mA/cm2; F.F. = 71.75 %時，光電轉換效率達17.26%。
;In this study, the intrinsic hydrogenated amorphous silicon (a-Si:H) thin films in heterojunction with intrinsic thin layer (HIT) solar cell was prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD). PECVD has several advantages, such as stable deposition rate, good coverage uniformity, low temperature growth and easy integration with other processes. The passivation quality of a-Si:H thin films was investigated by tuning the process parameters such as power, dilution ratio, and substrate temperature. Firstly, the thin film properties were measured and analyzed by Spectroscopic Ellipsometer. And the surface passivation quality of a-Si:H was determined by photo-conductance lifetime tester. Finally, a-Si:H films were applied to amorphous silicon / crystalline silicon heterojunction solar cells and improved the open-circuit voltage of solar cells.
The results show that the 50nm a-Si:H films can obtained high effective lifetime and good passivation quality for all process parameters with as-deposited condition, but after annealing treatment the passivation quality will decay because the Si-H bonds become disorder thus result in the reduction of effective lifetime. On the other hand, for the ultra-thin (5nm) a-Si:H films, after annealing treatment the effective lifetime increased. The high crystalline volume fraction will generated defects in the films or interface, after annealing process can improved the defects ratio, increase the Si-H bond at the substrate interface and compensate the surface dangling bonds, reduce recombination center and thus enhance the lifetime, that also prove the best passivation quality can be obtained with suitable amorphous to microcrystalline transition region. For ultra-thin (5nm) a-Si:H films, we obtained the high passivation quality under the condition of H2/SiH4=4, power of 20W, substrate temperature of 140℃, and after annealing process under the temperature 300 ˚C for 120 sec. The effective lifetime of a-Si:H film increased to 1.2 msec, the implied Voc increased to 0.694 V and cause the surface recombination velocity (SRV) decreased to 10 cm/s. In addition, the lifetime can reach 4.7 msec, implied Voc 0.725 V, the SRV drops to 2.98 cm / s on the 4-inch FZ-n silicon substrate. Moreover, the characteristics of HIT solar cell on CZ-n silicon substrate were shown as follow: Voc = 0.66 V, Jsc = 36.71 mA/cm2, F.F. = 71.75 %, efficiency = 17.26 % in the area of 1 cm2. |
