臺灣博碩士論文加值系統

本論文主要研究p-i-n結構砷化鎵太陽電池的光電特性，藉由改變本質層(i-layer)厚度，量測出最佳轉換效率的太陽電池結構。照光下電壓-電流的量測結果顯示，本質層厚度為1nm的樣品之轉換效率，優於沒有本質層結構的樣品，可達最高的效率14.24％。
接著利用光激螢光以及時間解析光譜，進一步得到不同本質層厚度時之侷限深度(localization depth)與輻射載子生命期(radiative lifetime)。實驗結果顯示，在1 nm本質層中有最佳侷限深度在9.8 meV和輻射載子生命期5.3 ns。產生侷限效應的原因是由於鋅擴散至負型砷化鎵和本質層。因此以650℃進行退火、在不同時間模擬鋅擴散，發現退火時間愈長，侷限深度愈高、輻射載子生命期也隨之愈短。在ECV測量中，它清楚証實鋅的濃度是在回火後有顯著地變化。亦即鋅確實擴散至負型砷化鎵和本質層。
此外進一步量測各個樣品光激螢光的變化來討論由缺陷所引起的表面複合速率(surface recombination velocity)，也發現在本質層結構為1 nm太陽能電池的表面複合速率有明顯的改善。綜合實驗結果顯示在太陽能電池上適當地增加本質層厚度是有助於提高轉換效率。

In this thesis, we reported the optoelectronic characteristics of p-i-n GaAs solar cells. We studied the optimum thickness of intrinsic layer for obtaining the highest conversion efficiency. The samples without were detected by current-voltage measurement under AM1.5G illumination that the sample with 1 nm intrinsic layer has the highest efficiency of 14.24％.
Based on low temperature photoluminescence and time resolved photoluminescence measurement, localization depth in such intrinsic layer thickness was developed. The experimental result showed that both localization depth (Eloc) at 9.8 meV and radiative lifetime (τrad) at 5.3 ns were achieved the best optoelectronic performance in 1 nm intrinsic layer. It was found out that the localization formed due to Zn diffusion in n-GaAs and intrinsic layer. Different samples annealed at 650℃ with different annealing time were attained to obtain the localization depth. It was clearly revealed that the longer annealed time, leads to the deeper localization, and to the shorter life time. The ECV measurements manifest that the Zn concentrations are changed dramatically. The evidence shows clearly that the Zn presented nominally in the lower n-GaAs and i-GaAs layer, as the result of diffusion.
Furthermore, it was proposed to distinguish the front surface recombination velocity from the induced defects by variation the PL intensity. From this photoluminescence measurement, the surface recombination velocity of the solar cells with the intrinsic layer 1 nm is obviously improved. As these results, the thickness of intrinsic layer indeed deeply influences the efficiency of solar cell.

Content
摘要 I
Abstract III
誌謝 V
Content VI
Figure Captions VIII
List of Tables XI
Chapter 1 1
Chapter 2 3
2.1 Photoluminescence(PL) 3
2.2 Time-Resolved Photoluminescence(TRPL) 6
2.3 Basic theories of solar cell 9
2.3.1 Solar spectrum 9
2.3.2 Photovoltaic effect 11
2.3.3 Equivalent circuit of a solar cell 13
2.3.4 Fundamental solar cell parameters 15
2.3.5 Series resistance of solar cell measurement 16
Chapter 3 18
3.1 p-i-n structure GaAs single solar cell 18
3.2 PL analysis Surface Recombination Velocity 20
Chapter 4 23
4.1 Electrical characteristics 23
4.2 Optical properties 27
4.2.1 PL spectra of p-i-n GaAs single solar cells 27
4.2.2 TRPL of p-i-n GaAs single solar cells 29
4.3 ECV of p-i-n GaAs solar cell 39
4.4 PL analysis to surface recombination velocity 41
Chapter 5 44
References 46
作者簡歷 49


Figure Captions

Fig. 2.1 Schematic diagram of band-edge photoluminescence processes in semiconductors. 4
Fig. 2.2 Photoluminescence experiment system 5
Fig. 2.3 Schematic diagram of TCSPC process 7
Fig. 2.4 Time-Resolved Photoluminescence experiment system 8
Fig. 2.5 Spectral distribution of sunlight power density including black body at 5250℃ 9
Fig. 2.6 The method to estimate the air mass 11
Fig. 2.7 Energy diagram of a solar cell (dark) 12
Fig. 2.8 Energy diagram of a solar cell (illuminated) 12
Fig. 2.9 Equivalent circuit of solar cell 13
Fig. 2.10 Current-voltage characteristics of solar cell 15
Fig. 3.1 Schematic cross-sections of the p-i-n structure GaAs single junction solar cell 18
Fig. 4.1 Illuminated I-V curve of different intrinsic layer p-i-n GaAs single solar cells under AM 1.5 G. 23
Fig. 4.2 Variation conversion efficiency for p-i-n GaAs single solar cells with different thickness intrinsic layer. 24
Fig. 4.3 Variation of series resistance with varying thickness for p-i-n GaAs single solar cells. 26
Fig. 4.4 15K PL spectra of p-i-n GaAs single solar cells with different thickness intrinsic layer. 28
Fig. 4.5 15K PL spectrum and fit data of p-i-n GaAs single solar cell without intrinsic layer. 28
Fig. 4.6 The TRPL measured sample without intrinsic layer, with energy peak 1.488eV at 15K. 29
Fig. 4.7 PL decay profile of sample without intrinsic layer excited by different emission photon energy 30
Fig. 4.8 PL spectra of solar cell without intrinsic layer (black solid lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 31
Fig. 4.9 PL spectra of solar cell with 1 nm thickness intrinsic layer (black solid lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 33
Fig. 4.10 PL spectra of solar cell with 5 nm thickness intrinsic layer (black solid lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 33
Fig. 4.11 PL spectra of solar cell with 20 nm thickness intrinsic layer (black solid lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 34
Fig. 4.12 Variation Eloc and conversion efficiency with varying thickness for GaAs solar cell. 35
Fig. 4.13 PL spectra of solar cell with 1 nm thickness intrinsic layer after annealing at 650℃ for 20 s (black soild lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 36
Fig. 4.14 PL spectra of solar cell with 1 nm thickness intrinsic layer after annealing at 650℃ for 30 s (black soild lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 36
Fig. 4.15 PL spectra of solar cell with 1 nm thickness intrinsic layer after annealing at 650℃for 60 s (black soild lines). The open circles display the emission-energy dependence of lifetime τ. The blue solid lines match the calculated τ using Eq. (4-4). 37
Fig. 4.16 Variation Eloc and τrad for GaAs solar cell of intrinsic layer 1 nm with annealing at different annealing time at temperature 650 ℃. 38
Fig. 4.17 ECV depth profile of Zn concentration in the p-i-n solar cell at different annealing times 39
Fig. 4.18 The influence of surface recombination velocity on minority carrier lifetime and the relative PL intensity for p-i-n GaAs solar cells with different intrinsic layer 41
Fig. 4.19 The influence of surface recombination velocity on minority carrier lifetime and relative PL intensity for p-i-n GaAs solar cells with different annealing times at 650℃ 43


List of Tables

Table 4.1 Variation of characteristics for p-i-n GaAs single solar cells with different i-layer thickness under AM 1.5 G. 25
Table 4.2 Variation of series resistance with varying thickness for p-i-n GaAs single solar cells. 25
Table 4.3 Variation of τrad, Eme and Eloc for p-i-n GaAs single solar cells with i-layer thickness. 34
Table 4.4 Variation of τrad, Eme and Eloc for p-i-n GaAs single solar cells after annealing at 650℃for different time duration. 37
Table 4.5 Variation of τ and S for with different intrinsic layer thickness p-i-n GaAs single solar cells. 42
Table 4.6 Variation of τ and S with different annealing times for p-i-n GaAs single solar cells. 43

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