具銻砷化鎵間隔層之偶合砷化銦量子點與晶格匹配之磷砷氮化鎵應用於中間帶太陽能電池及薄膜太陽能電池

Coupling InAs Quantum Dot with GaAsSb as Spacer and Lattice-matched GaNAsP Applied to Intermediate Band Solar Cell and Thin Film Solar Cell

林延儒(Yen-Ju Lin)

指導教授 ： 郭茂坤

國立臺灣大學/工學院/應用力學研究所/博士(2022年)

https://doi.org/10.6342/NTU202200565

摘要

中間帶太陽能電池被認為是能夠提升太陽能電池轉換效率的一種設計。本研究以線性彈性力學理論、k p漢彌爾頓配合有限元素法分析以銻砷化鎵(GaAsSb)作為間隔層之偶合砷化銦(InAs)量子點結構。本研究分析量子點結構中各材料之摩爾分率與厚度對光學性質的影響，進而評估結構應用於中間帶太陽能電池之最佳參數。當GaAsSb間隔層中Sb摩爾分率增加至0.24將使能帶結構轉換成第二型態，而所形成中間帶之寬度，主要受到間隔層厚度之影響，Sb摩爾分率改變只稍微影響中間帶之能量。而在偶合型量子點結構中加入1 nm厚之AlAs層與1 nm厚之GaAs層將有助於將中間帶至導電帶吸收光譜推向近紅外光區域，同時在分析利用InAs偶合型量子點作為中間帶太陽能之轉換效率時，中間帶之寬度及價電帶與導電帶之間的能隙大小為重要因素，而採用飄移擴散模型並忽略復合效應的狀況下，當集中因子為1000時，GaAs太陽能電池轉換效率為32.9%，而由8.5 nm組成之Sb摩爾分率為0.1的GaAsSb間隔層偶合型量子點結構做為中間帶太陽能電池轉換效率則有34.1%。
高度不匹配化合物也是能應用於中間帶太陽能電池的一種材料，本研究選擇磷砷氮化鎵(GaNAsP)作為分析的材料。本研究使用能帶反交叉模型推導出適用於塊體GaNAsP之吸收光譜，並利用可與GaP達成晶格匹配的條件來設計中間帶太陽能電池，結果發現由於與當作中間帶之E− c能帶有關之兩段吸收間強度相差太大，其作為中間帶太陽能電池的轉換效率僅有11.4%，相較於無中間帶的磷化鎵(GaP)電池只增加0.8%。
本研究設計與矽達成晶格匹配條件的GaNAsP/Si疊層太陽能電池。我們採用飄移擴散模型並忽略復合效應與次電池間的中間層，以此評估太陽能電池轉換效率極大化。本研究分析了GaNAsP的摩爾分率組合與不同的厚度組合，研究成果顯示，疊層太陽能電池轉換效率優於單純由矽所形成的太陽能電池。4.5 m厚的疊層太陽能電池可提供12.5 %的轉換效率，等同於10.7 m厚的矽電池轉換效率。11.5 m厚的疊層太陽能電池可提供20.2 %的轉換效率，而同樣厚度的矽電池僅能提供12.7 %的轉換效率。同時，當疊層太陽能電池總厚度在12 m以下時，矽電池厚度比例在45%至70%時，疊層太陽能電池會有最高的轉換效率，而該比例則取決於疊層太陽能電池的總厚度。

關鍵字

有限元素法 ； 偶合型量子點 ； 銻砷化鎵 ； 磷砷氮化鎵稀氮化合物 ； 中間帶太陽能電池 ； 疊層太陽能電池 ； 超薄太陽能電池

並列摘要

Intermediate band solar cell (IBSC) is a design to improve the power conversion efficiency (PCE) of a solar cell. This study analyzes the optical properties of InAs coupling quantum-dot (QD) with GaAsSb as a spacer. A model based on theory of linear elasticity, k p theory is developed to study the mole fraction and the layers’ thicknesses of InAs coupling quantum-dot for IBSC application.
Numerical results show that InAs/GaAsSb coupling QD has type-II band structure with 24% Sb in GaAsSb spacer. The bandwidth of the intermediate band (IB) mainly depends on the thickness of GaAsSb spacer, while the Sb concentration slightly affect the energy. With 1 nm GaAs layer and 1 nm AlAs layer, the absorption spectrum between IB to conduction band (CB) can be put to near infrared range. The bandwidth of the IB and the bandgap between valence band and CB are important factor for IBSC power conversion efficiency (PCE). Based on model in this thesis with 1000 concentration ratio, GaAs solar cell has 32.9% PCE，while the IBSC, composes of InAs/GaAsSb0.1 coupling quantum-dot with 8.5 nm GaAsSb spacer, has 34.1% PCE.
Highly mismatch alloys (HMAs) are considered as materials suitable for IBSC application. The absorption spectrum of bulk GaNAsP is derived by band anti-crossing model. An IBSC with GaP-lattice-matched GaNAsP is analyzed. However, because of the huge difference between the two section absorption spectrum, the IBSC only has 11.4% PCE, only 0.8% higher than a GaP solar cell. GaNAsP can be lattice matched with Si for GaNAsP/Si tandem cell design. The numerical results show that GaNAsP/Si tandem cell has superiority than a Si solar cell. A 4.5 m GaNAsP/Si tandem cell can provide 12.5% PCE, same as a 10.7 m Si cell. An 11.5 m GaNAsP/Si tandem cell can provide 20.2% PCE, a Si cell with the same thickness is only 12.7%. Meanwhile, for tandem cells with thickness below 12 m, the tandem cell with the Si-thickness- ratio cell between 45% to 70% will have maximum PCE. The Si-thickness- ratio depends on the total thickness of the tandem cell.

並列關鍵字

finite element method ； coupling quantum dot ； GaAsSb ； GaNAsP ； intermediate band solar cell ； tandem cell ； ultra thin solar cell

參考文獻

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