無投影片標題

Size: px

Start display at page:

Download "無投影片標題"

千终
4 years ago
Views:

1 第六章光伏元件 261

2 目錄 6-1 太陽能光譜 6-2 光伏元件的原理 6-3 pn 接面光伏 I-V 特性 6-4 串聯電阻和等效電路 6-5 溫度效應 6-6 太陽能電池材料, 元件和效率 262

3 6-1 太陽能光譜 263

4 Spectral Intensity dw cm -2 (µm) -1 or kw m -2 (µm) Black body radiation at 6000 K AM0 AM Wavelength (µm) The spectrum of the solar energy represented as spectral intensity (I λ ) vs wavelength above the earth's atmosphere (AM0 radiation) and at the earth's surface (AM1.5 radiation). Black body radiation at 6000 K is shown for comparison (After H.J. Möller, Semiconductors for Solar Cells, Artech House Press, Boston, 1993, p.10) From S.O. Kasap, Optoelectronics and Photonics: Principles and Practices (Prentice Hall) 264

5 AM0 h 0 Atmosphere h θ α α Earth AM1 AM(secθ) (a) Tilted PV device Direct (b) Diffuse (a) Illustration of the effect of the angle of incidence θ on the ray path length and the definitions of AM0, AM1 and AM(secθ). The angle α between the sun beam and the horizon is the solar latitude (b) Scattering reduces the intensity and gives rise to a diffused radiation?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 265

6 266

7 6-2 光伏元件的原理 267

8 Neutral n-region E o Neutral p-region Long λ Drift Diffusion Medium λ Short λ L e Back electrode Finger electrode L h n Depletion region W p V oc The principle of operation of the solar cell (exaggerated features to highlight principles)?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.3 太陽能電池的工作原理 ( 跨大的圖形以放大工作原理 ) 268

9 Finger electrodes Bus electrode for current collection n p Finger electrodes on the surface of a solar cell reduce the series resistance?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.4 太陽能電池表面上的文叉指型電極可降低串聯電阻 269

10 EHPs exp( αx) x L h W L e I ph Photogenerated carriers within the volume L h + W + L e give rise to a photocurrent I ph. The variation in the photegenerated EHP concentration with distance is also shown where α is th absorption coefficient at the wavelength of interest.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.5 在 L n + W +L e 體積內光產生的載子造成光電流 I ph 光產生電子電洞對濃度隨著距離的改變也圖示在這裡, α 是有興趣波長的吸收係數 270

11 271

12 272

13 6-3 pn 接面光伏 I-V 特性 273

14 假如是光的強度, 那麼短路電流 (short circuit current) 為 I sc = I ph = KI (1) 274

Light I I sc = I ph I = I d I ph V V = 0 I ph V I d I ph R (a) (b) (c) (a) The solar cell connected to an external load R and the convention for the definitions of positive voltage and positive

15 Light I I sc = I ph I = I d I ph V V = 0 I ph V I d I ph R (a) (b) (c) (a) The solar cell connected to an external load R and the convention for the definitions of positive voltage and positive current. (b) The solar cell in short circuit. The current is the photocurrent, I ph. (c) The solar cell driving an external load R. There is a voltage V and current I in the circuit.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) R 275

16 276

17 277

18 I (ma) 20 Dark 0 I ph V oc 0.6 V Light?0 Twice the light Typical I-V characteristics of a Si solar cell. The short circuit current is I ph and the open circuit voltage is V oc. The I-V curves for positive current requires an external bias voltage. Photovoltaic operation is always in the negative current region.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.7 一個太陽能電池的典型 I-V 特性, 短路電流為 I ph, 開路電壓為 V oc ; 對於正電流的 I-V 曲綫需要一個外加偏壓, 光伏應用都是用在負電流區 278

Light I I (ma) 0 0.2 0.4 V V oc 0.6 V I R V I sc = I ph 10 20 Slope = 1/ R I P I-V for a solar cell under an illumination of 600 Wm -2.

19 Light I I (ma) V V oc 0.6 V I R V I sc = I ph Slope = 1/ R I P I-V for a solar cell under an illumination of 600 Wm -2. Operating Point The Load Line for R = 30 ž (I-V for the load) (a) (b) (a) When a solar cell drives a load R, R has the same voltage as the solar cell but the current through it is in the opposite direction to the convention that current flows from high to low potential. (b) The current I and voltage V in the circuit of (a) can be found from a load line construction. Point P is the operating point (I, V ). The load line is for R = 30 ž.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 279

20 填充因子 (fill factor) FF 是太陽能電池的重要指標, 定義成 I mvm FF = (4) I V sc oc 280

21 281

22 282

23 283

24 284

25 假設 V >> nkb 們得到 V oc 為 oc T / e, 重新整理上面的方程式, 我 V oc = nk B e T ln I I ph o (5) 285

26 6-4 串聯電阻和等效電路 286

27 Neutral n-region Depletion region Neutral p-region Finger electrode R s Back electrode R p R L Series and shunt resistances and various fates of photegenerated EHPs.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.9 串聯與分流電阻和光產生電子電洞對的不同際遇 287

28 288

29 0 0 V oc R s = 50 Ω V 5 R s = 0 R s = 20 Ω I sc I ph 10 I (ma) The series resistance broadens the I-V curve and reduces the maximum available power and hence the overall efficiency of the solar cell. The example is a Si solar cell with n 1.5 and I o ma. Illumination is such that the photocurrent I ph = 10 ma.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.11 串聯電阻會使 I-V 曲綫變寬, 並降低最大可能功率, 因此使得太陽能電池的整體效率降低圖中的例子是矽製太陽能電池, 且 6, 照光使得光電流 I = 10 ma n 1.5 I o 3 10 ma ph 289

30 290

31 6 Power (mw) Voltage (V) cell cells in parallel 20 Current (ma) Current vs. Voltage and Power vs. Current characteristics of one cell and two cells in parallel. The two parallel devices have R s /2 and 2I ph.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.12 一個電池和兩個並聯電池的電流對電壓與功率對電流的特性兩個並聯元件有 R / 2 和 2I s ph 291

32 292

33 I ph R s I/2 A I/2 R s I d I I d I ph V R L I ph B Two identical solar cells in parallel under the same illumination and driving a load R L.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.13 在相同照光強度之下的兩個太陽能電池並聯且推動一個負載 R L 293

34 6-5 溫度效應 294

35 295

36 296

37 6-6 太陽能電池材料, 元件和效率 297

38 100% Incident radiation 0.74 Insufficient photon energy hυ < E g 0.59 Excessive photon energy Near surface EHP recombination hυ > E g 0.95 Collection efficiency of photons 0.6 V oc (0.6E g )/(ek B ) 0.85 FF 0.85 Overall efficiency η 21% 圖 6.14 算 Accounting for various losses of energy in a high efficiency Si solar cell. Adapted from C. Hu and R. M. White, Solar Cells (McGraw-Hill Inc, New York, 1983, Figure 3.17, p. 61).?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 在一個高效率矽製太陽能電池中, 不同能量損失的計 298

39 Oxide p n Light L e Inverted pyramid textured surface substantially reduces reflection losses and increases absorption probability in the device?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.15 倒金字塔的織狀表面可大量的降低反射損失, 並增加元件的吸收機率 299

40 300

41 p-algaas window (< 0.02 µm Passivated GaAs surface p-gaas n-gaas AlGaAs window layer on GaAs passivates the surface states and thereby increases the low wavelength photogeneration efficiency?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.16 在 GaAs 上面的 AlGaAs 視窗層覆蓋表面狀態, 因此會增加短波長的光產生效率 301

42 n AlGaAs p GaAs (a) E c 2 ev 1.4 ev E c E v (b) E v A heterojunction solar cell between two different bandgap semiconductors (GaAs and AlGaAs)?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.17 池兩不同能帶間隙半導體材料間的異質接面太陽能電 302

43 Connecting region. p n p n Cell 1 (E g1 ) Cell 2 (E g2 < E g1 ) A tandem cell. Cell 1 has a wider bandgap and absorbs energetic photons with hυ > E g1. Cell 2 absorbs photons that pass cell 1 and have hυ > E g2.?1999 S.O. Kasap, Optoelectronics (Prentice Hall) 圖 6.18 一種串聯式的電池, 電池 1 有寬的能帶間隙可吸收的高能光子, 電池 2 吸收 h υ > E g 2 通過電池 1 的光子 h υ > E g1 303

Microsoft PowerPoint - Ch5 The Bipolar Junction Transistor

Microsoft PowerPoint - Ch5 The Bipolar Junction Transistor O2005: Electronics The Bipolar Junction Transistor (BJT) 張大中中央大學通訊工程系 dcchang@ce.ncu.edu.tw 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 1 Bipolar Transistor Structures N P 17 10 N D 19 10 N D 15 10 中央大學通訊系張大中