Structure Design And Performance Simulation Of Nc-Si Heterojunction Device

In this thesis, nanocrystalline Si based heterojunction devicesincluding high electron mobility transistor (HEMT) of nanocrystalline Si/crystalline Si (nc-Si/c-Si) heterojunction, tandem double junction solarcell of amorphous Si/nanocrystalline Si (a-Si/nc-Si) and intermediateband solar cell with Si based quantum dots were investigated withnumerical simulation method, and the performance of these three kindsunits were analyzed.(â…°). Firstly, the influence of interface state densities in nc-Si:H/c-Si:Hheterojunction HEMT on the performance of the device was investigated.The results show that the DC output current increases with increasinginterface state densities, which can be allocated to the increase ofinterface state densities under channel electric filed and leading moreionized electrons to participate conduction. The DC output current isproportional to the mean size of nc-Si grains under the same interfacestate densities. Since the disorder degree of nc-Si films increases with theaverage size decrease, the electronic mobilities of material reduce, whichleads the output current to decrease.(â…±). A kind of a-Si:H/nc-Si:H tandem solar cell was designed. Via theAMPS-1D software, the numerical simulation of the cell was carried outto obtain the suitable thickness of intrinsic layer of the sub-cell. Based onoptimization of the sub-cells, chosing the nc-Si material as a tunneljunction layer of2nm in the cell, the perfect performance can beobtained.(â…²). Under the condition of full light focusing, the maximum limitefficiency of intermediate band solar cell with nc-Si quantum dots atdifferent intermediate band positions was numerical calculated. Inaddition, one can learn that the maximum efficiency of this kind solar cellcorresponds to operating voltage of about1.20V through the study the relation between output efficiency and operating voltage.