臺灣博碩士論文加值系統

本論文研究主要為製作一系列單一接面GaAs與InGaP太陽電池，主要重點著重於元件中最重要的主動層(base layer)，在半導體中影響材料電特性最大的便是摻雜濃度，摻雜濃度太高時，元件中的短路電流會減少而開路電壓會隨之增加，反之兩輸出特性亦顛倒過來，而元件中不同的主動層厚度會有不同的光吸收量，較厚雖然可增加光吸收量，但相對地串聯電阻、暗電流等對元件有退化影響的參數會因厚度增加而增加，上述幾點都會影響太陽電池的轉換效率，故本實驗利用改變不同主動層厚度與主動層摻雜濃度，找出影響元件輸出電特性因素與最佳平衡點，以便獲得元件的最佳轉換效率。
在雙接面太陽電池結構中，因為主結構為兩電池以串聯方式連接，因此會有電流匹配問題，故設計上較為複雜，這裡便以先前單一接面太陽電池的實驗結果來當作設計雙接面太陽電池的基準，而此實驗主要重點會落在上部子電池(InGaP subcell)的主動層厚度設計，藉由調整主動層厚度與光偏壓I-V電性量測便可找出電流限制子電池，進一步進行元件優化設計。
其所有元件皆做常溫與變溫電性量測，經由實驗結果來取得元件設計之最佳化及元件之熱穩定度探討。

The object of this study is to fabricate a series interconnected GaAs and InGaP solar cells respectively and particularly focuses on optimizing the most important part of these solar cells, base layer. For semiconductor devices, the carrier concentration influences the electrical properties of the materials. Both the short-circuit current and open-circuit voltage of the solar cell decreases with increasing carrier concentration. In addition, the layer thickness is another essential issue of the output electrical characteristics of device. A thicker layer will absorb more quantity of incident light, but too thick a layer causes an increase in both series resistance and dark current, which will degenerate the performance of the device. We found the optimum values for the thickness and concentration of the device’s active layer through this study.
The DJ solar cell is made up of GaAs and InGaP SJ solar cell in series connection. The current mismatching between InGaP and GaAs subcells limits the total photocurrent of the device. We took the results of the SJ solar cell experiments as the references for the DJ solar cell design and the main experiment variable was the base layer thickness of InGaP subcell. By varying base layer thickness and using laser light-bias I-V measurement, one could find the current limited cell clearly and the optimal design of the device.
The current-voltage (I-V), external quantum efficiency (EQE) and thermal stability characteristics of the fabricated solar cells were measured by ISO-standard Simulator and homemade spectral response measurement system, respectively, at room and various temperatures.

Content
Abstract (Chinese)...........................................I
Abstract (English) ..........................................II
Acknowledgments............................................III
Figure Captions............................................VII
List of Tables..............................................IX

Chapter 1 Introduction.......................................1
1.1 The advantages of III-V alloys solar cell................1
1.2 The research points of the III-V solar cells.............2
1.2.1 GaAs and InGaP SJ solar cells..........................3
1.2.2 InGaP/GaAs DJ solar cell...............................4
Chapter 2 Basic theories of solar cell.......................4
2.1 Solar Radiation..........................................4
2.2 Basic principle of solar cell............................5
2.3 The equivalent circuit analysis of a solar cell..........6
2.4 Fundamental solar cell parameters........................7
2.5 Series resistance Rs of solar cell measurement...........8
Chapter 3 Experimental equipment systems and structural
details of the fabricated solar cell.........................9
3.1 MOCVD (Metal Organic Chemical Vapor Deposition)..........9
3.1.1 Introduction...........................................9
3.1.2 MOCVD for GaAs and InGaP compounds.....................9
3.2 Processes of fabricated solar cell......................11
3.2.1 GaAs, InGaP SJ solar cells............................11
3.2.2 InGaP/GaAs DJ solar cells.............................11
3.3 The measurement systems.................................12
3.3.1 Current-Voltage (I-V) characteristics of solar cell measurement.................................................12
3.3.2 Measurement of the spectral response of solar cell....13
3.3.2.1 Introduction........................................13
3.3.2.2 Spectral response measurement system................14
Chapter 4 Experiment results and discussion.................16
4.1 GaAs SJ solar cell......................................16
4.1.1 The I-V characteristics of the GaAs SJ solar cells at
various temperatures........................................16
4.1.2 The QE of the GaAs SJ solar cell at various
temperatures................................................18
4.1.3 The temperature dependent series resistance of the GaAs
SJ solar cell...............................................20
4.2 InGaP SJ solar cell.....................................20
4.2.1 The I-V characteristics of the InGaP SJ solar cells at
various temperatures........................................20
4.2.2 The QE of the InGaP SJ solar cell at various
temperatures................................................22
4.2.3 The temperature dependent series resistance of the
InGaP SJ solar cell.........................................23
4.3 InGaP/GaAs DJ solar cell................................23
4.3.1 The I-V characteristics of the InGaP/GaAs DJ solar cells
at various temperatures.....................................23
4.3.2 The QE of the InGaP/GaAs DJ solar cell at various
temperatures................................................26
Chapter 5 Conclusions.......................................27
5.1 InGaP and GaAs SJ solar cells...........................27
5.2 InGaP/GaAs DJ solar cells...............................27



Figure Captions
Figure 1.1 Past achievements and future predictions of
conversion efficiencies of various solar cells..............29
Figure 2.1 Spectral distribution of sunlight including black
body at 6000K, AM0 and AM1.5 radiation......................30
Figure 2.2 The way to estimate the air mass.................31
Figure 2.3 Energy band diagrams of solar cell...............31
Figure 2.4 Equivalent circuit of solar cell.................32
Figure 2.5 I-V characteristic of the circuit shown in Figure
2.3 equivalent to a solar cell..............................32
Figure 2.6 Determination of series resistance for solar
cell........................................................33
Figure 3.1 Schematics of InGaP SJ solar cell structures.....34
Figure 3.2 Schematics of InGaP SJ solar cell structures.....35
Figure 3.3 Schematics of InGaP/GaAs DJ solar cell
structures..................................................36
Figure 3.4 Schematic explanation of current mismatch for
monolithic DJ solar cell....................................37
Figure 3.5 Schematic representation of the spectral response
measure- ment system for single- and multi-junction solar
cells.......................................................37
Figure 4.1 The variations of (a) ISC (b) VOC (c)Eff. as a
function of temperature for the samples described in
Table 4.1...................................................39
Figure 4.2 (a-e) Spectral responses of the samples, GaAs-1
to GaAs-5, measured at various temperatures.................42
Figure 4.3 (a-e) Temperature dependent redshift of spectral
response for GaAs-1 to GaAs-5...............................44
Figure 4.4 (a-f) I-V curves of the samples, GaAs-1 to GaAs-6,
measured at various temperatures............................47
Figure 4.5 Temperature dependent series resistance of the
fabricated GaAs solar cells.................................47
Figure 4.6 The variations of (a) ISC (b) VOC (c)Eff. as a
function of temperature for the samples described in
Table 4.2...................................................49
Figure 4.7 (a-d) Spectral responses of the samples, InGaP-1
to InGaP-4, measured at various temperatures................51
Figure 4.8 (a-d) Temperature dependent redshift of spectral
response for InGaP-1 to InGaP-4.............................53
Figure 4.9 Temperature dependent series resistance of the
fabricated GaAs solar cells.................................54
Figure 4.10 The variations of (a) ISC (b) VOC (c)Eff. as a
function of temperature for the samples described in
Table 4.3 ...................................................57
Figure 4.11 (a-c) Spectral responses of the samples, D-1 to
D-3, measured at various temperatures.......................59



List of Tables
Table 2.1 -The standard of Air Mass versus power per unit
area determined by NASA.....................................30
Table 3.1 -Thickness and doping concentration of the InGaP
solar cells.................................................34
Table 3.2 -Thickness and doping concentration of the GaAs SJ
solar cells.................................................35
Table 3.3 -Active layer thickness of the InGaP/GaAs DJ solar
cells.......................................................36
Table 4.1 -Device characteristics of GaAs solar cell at AM0.38
Table 4.2 -Device characteristics of InGaP solar cell at
AM1.5G......................................................48
Table 4.3 -The electrical output characteristics of the DJ
solar cells.................................................55
Table 4.4 -The thermal coefficients of temperature dependent
ISC between DJ solar cells and their subcells...............55
Table 4.5 -The thermal coefficients of temperature dependent
VOC for samples, GaAs-3, InGaP-1, D-2.......................55

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