矽晶太陽能電池之理論效率分析、特性模擬與製程技術

The theoretical analysis of limiting efficiency, simulation of characteristics and process technique for crystalline silicon solar cell

盧俊安(Chun-An Lu)

指導教授 ： 劉致為

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.10341

摘要

由於矽晶太陽能電池的高轉換效率及高穩定性，此技術已被廣泛使用在太陽能產業上，雖然矽晶太陽能電池的技術已經趨於成熟，但是在高轉換效率( >20% )的技術上仍有許多挑戰。
本論文中，我們製作並討論利用N型矽晶圓做為基板的太陽能電池，此方法有別於市售一般P型矽晶圓的產品，另外對於高轉換效率的結構，我們嘗試使用HIT結構的太陽能電池。首先，我們計算矽基太陽能電池的理論轉換效率，利用此理論模型，可以輕易得知實驗和理論值的最大差距主要來自於元件的逆向飽和電流。
N型太陽能電池的製程主要利用離子佈值技術來製作元件的射極及背面電場，在合適的離子佈值、快速熱退火、電極製作的條件下，最高的光電轉換效率為11.8%，藉由量測元件的暗電流，來調變製程參數，此外，利用非晶矽層製作太陽能電池射極的HIT結構達到的最高效率為11%。
矽晶太陽能電池的發展趨勢為降低矽晶圓的厚度以減少成本，但隨著厚度的降低，表面復合速度對元件的影響會愈趨顯著，我們對表面復合速率在不同厚度下如何影響元件的光電流及暗電流進行模擬，結果顯示正面的復合速率對量子效率有很大的影響，進一步影響元件的短路電流，另外，背面的復合速率主要影響元件的暗電流，因此對開路電壓影響較大。
最後，我們利用濕式蝕刻的方式，在矽晶圓表面形成奈米線陣列的結構，此結構能夠有效降低入射光的反射率至小於5%，比起傳統鹼蝕刻製程的反射率降低了約7-8%。此外，我們利用光學量測的方式如準穩態光電導方法及光激發光光譜技術對蝕刻後表面的品質做分析，並和傳統的鹼蝕刻製程做比較。

關鍵字

理論轉換效率/異質接面薄本質層/表面復合速率/奈米表面紋理/準穩態光電導方法

並列摘要

Wafer based solar cell has been widely adopted by the photovoltaic industry due to its high efficiency and stability. The wafer cell technology has already been mature for conventional structure. However, there are still lots of new challenges existing for the high efficiency solar cell (η>20%).
In this thesis, the wafer based solar cell made of n-type silicon wafer and the heterojunction with intrinsic thin layer (HIT) structure are demonstrated. First, the limiting efficiency of solar energy conversion is discussed to show the maximum efficiency of crystalline silicon solar cell. By applying the theoretical model, it can be easily realized that the gap existing in the efficiency limit and the state-of-the-art solar cell is cause by the difference in dark saturation current.
Next, the fabrication process of n-type substrate silicon solar cell is demonstrated by using ion implantation to form the emitter and back surface field. The suitable implantation, rapid thermal annealing and contact formation conditions were found. An efficiency of 11.8% is showed in this work. Dark saturation current was taken into consideration while optimizing the process parameters. The HIT solar cell was also demonstrated, with an efficiency of 11%, to investigate the benefits of using amorphous silicon as emitter.
On the other hand, simulation on the influence of surface recombination velocity (SRV) was while reducing the thickness of the substrate. The results showed that the short circuit current has strong dependence of the value of front SRV while the open circuit voltage has strong dependence on back SRV. With thinner substrate, the issue of surface passivation becomes very crucial to the cell efficiency.
Finally, a new method of texturing the wafer surface with weighted reflectance less than 5% was demonstrated and compared to the conventional texture technique. The nano-textured wafer shows high potential for further improving wafer based solar cell efficiency as long as the the surface can be well passivated. The quality of the surface after different texture method was characterized by optical measurement such as quasi-steady-state photoconductance and photoluminenscence.

並列關鍵字

Efficiency limit/HIT/SRV/Nano-texture/QSSPC

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