太阳能光伏讲义Lecturenote5.doc

L5 1 PHOTOVOLTAIC TECHNOLOGY Absorption of light ? Ifa photon has E ph>E g? absorption. L5 2 L5 3 ?“ Blue ” light (short ?< 500nm) is absorbed more strongly than red ( ?~ 650nm) or IR(?> 750 nm) radiation in Si. That is ina Si solar cell blue light is absorbed closer to the front surface than red light. ? Generation rate of electron-hole (e-h) pairs per unit volume, G [‘ number of e-h ’/cm 3 /s].N=# of photons/cm 2 /s at surface G=α Ne –αxα= absorption coefficient [cm -1]x= distance [cm] L5 4 bination Electron- hole pairs generated by light ina semiconductor layer will eventually bine (R)- “ reverse ” process of the generation process (G). ? The carrier lifetime =average time for bination to occur after electron- hole generation.~ 10 μs for Si. ? The carrier diffusion length = average distance a carrier will move (due to the