太陽能電池的工作原理 Semiconductor-Energy band 射防止膜 Refed-Proof Film 型半哪 N-Type Semiconduct :。sm Energy aap Sp甲 D半海曾 p-Type Semiconductor I we far apart atoms Iwe close atoms 太光鼋粒子 A K Cha, Nated Sun Ya-sen Univers Semiconductor -Fermi level Semiconductor -Drift and diffusion At thermal equilibriu, Fermi function describes hss action lay the probability that a state at energy E Is nilled by Diffusion where Ey b a refereace energy called HDPe LE,E, Energy lasses due to eel states at energy E whih are less than Er are mostly nlle: States at energy E which are larger than Er are mostly unoccupied. EE+ d 0 d Carier concentrations in conduction band and E valence bands are E,MMm“t4rd= where 一gErn=v D,=-4: Diffusa eeeficirat J=∑-=-=啊只E N-2 25m yx Efecthe dreary f tate of rance ad 口J= A k Chu Natal Sun Ya sen Unverse A.K. Cha, Natonal Sun Ya-sen Universty
21 太陽能電池的工作原理 22 Semiconductor-Energy band A. K. Chu, National Sun Yat-sen University 23 Semiconductor-Fermi level A. K. Chu, National Sun Yat-sen University 24 Semiconductor-Drift and diffusion A. K. Chu, National Sun Yat-sen University
Semiconductor- pn homojunction Depletion region width Forward bias N., n intrinsic carrier density r,=r, tr E w n, for Si is 1 45xl0cm =+,mV0 imbrium, the Fermi-leel Example A lightly doped, n-type Si has a resistivity 几 Reverse bias higher than that in then-type Si What is the build. Forward bias,3,\ 南, in voltage at the junction E.5 For a resistivity of 4@2-cm,\, =105 cr. e, for Si is 11.7, and t-8.854x10 Fcm dMMN, =0.753 Depletion region width: x“x 125(+=0=10 A.K. Chu, Natonal Sun Yasen Unversity A K Cha, Nated Sun Ya-sen Univers Photovoltaic effect Operation of photovoltaic device Si Energy band diagram a The operation of the photovoltaic device follows v-o(thermal eguilibrium by D e-h pairs creation by photons absorption D Separation of e-h pairs before recombination n Transportation of free e and h to electrodes +V=% Flat band count Heat <<KI A k Chu Natal Sun Ya sen Unverse
25 Semiconductor- pn homojunction A. K. Chu, National Sun Yat-sen University 26 A. K. Chu, National Sun Yat-sen University 27 Photovoltaic effect A. K. Chu, National Sun Yat-sen University 28 Operation of photovoltaic device(I) The operation of the photovoltaic device follows by e-h pairs creation by photons absorption Separation of e-h pairs before recombination Transportation of free e and h to electrodes
Operation of photovoltaic device () Operation of photovoltaic device(l) Transportation Carrier recombination Quasi-neutral region Diffusion length, L, Carriers move by difFusion L, "D, p Carrier recombination carrier lifetime of hole Use, cm Quasi-neutral [Depletion: Quasi-neutral Quasi-neutral Depletion; Quasi-neutral D,-12(m/sec eglon Carriers move by drifting A.K. Chu, Natonal Sun Yasen Unversity A K Cha, Nated Sun Ya-sen Univers Fundamentals Metal-semiconductor contact e Photovoltaic effect results from_f Band diagram of metal-semiconductor interface incident light on some materials n-setnicondurter , PV effect promotes electrons higher energy conduction ban leaving holes behind . Separation of carriers, electrons ve)and holes(+ve)important to solar cells , +ve and-ve carriers transported fn"h x through material in all directions will now from K Ch, Natoma Sun Yasn Unrversty
29 Operation of photovoltaic device(II) A. K. Chu, National Sun Yat-sen University 30 Operation of photovoltaic device(III) A. K. Chu, National Sun Yat-sen University 31 Fundamentals Photovoltaic effect results from incident light on some materials PV effect promotes electrons into higher energy conduction bands, leaving holes behind Separation of carriers, electrons (- ve) and holes (+ve) important to solar cells +ve and –ve carriers transported through material in all directions Surface recombination Surface recombination Bulk recombination 32 Metal-semiconductor contact A. K. Chu, National Sun Yat-sen University
Tunneling contact Alloying contact Contact metals shottky barriers to si E N E E silicon type Metal q%r(eV) q%(ev) E x= 24 (9-2 N,4 A.K. Chu, Natonal Sun Yasen Unversity 串聯與分流(並聯)電阻 太陽能電池的等效電路 串聯電 R Pegler ■Rp分流(並聯)電 阻 lectrode ph RL Solar cell
33 A. K. Chu, National Sun Yat-sen University 34 35 串聯與分流(並聯)電阻 Rs:串聯電阻 Rp:分流(並聯)電 阻 36 太陽能電池的等效電路
串聯電阻會使V曲錢變寬 The Laws of Geometric Optics ■串聯電阻會使曲縵 tght travel in a straight line in a medium with constant n. 變寬 Incident angle of a light is equal to the reflection angle of the light. 口降低最大可能功率 Refraction (Snell's law) 口使得太陽能電池的 整體效率降低 ■Rs不會影響開路電 R=20日 Example n2“L,n2“15anda-3 Dielectric constant &=6,'s, 壓Voc,但低的Rp Pane ef incident 值會使Ⅴoc降低 xsm30°=15winb A K Cha, Nated Sun Ya-sen Univers Reflection and refraction of waves Reflection of Lights at Different Surfaces The direction of light propagation can be altered index of the medium
37 串聯電阻會使I-V曲綫變寬 串聯電阻會使曲綫 變寬 降低最大可能功率 使得太陽能電池的 整體效率降低。 Rs不會影響開路電 壓Voc，但低的Rp 值會使Voc降低 38 The Laws of Geometric Optics A. K. Chu, National Sun Yat-sen University 39 Reflection and Refraction of Waves 40 Reflection of Lights at Different Surfaces