| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 104 === This thesis aims at the improvement of back-junction type PEDOT:PSS/Si hybrid solar cells, which was first proposed and demonstrated by Zieke and coworkers with a decent power conversion efficiency.
The limited efficiency of current PEDOT:PSS/Si solar cells were basically due to the facts that the heterojunction was located on the front of the cell, resulting in a parasitic light absorption within the organic material. In addition, the rear surface of those front-junction solar cells was usually poorly passivated. To overcome above difficulties, one must place the PEDOT:PSS on the rear side of the device and the solar cell must be fabricated on a thin Si wafer to reduce carrier recombination. By adapting back contact cross-finger type PEDOT:PSS/Si heterostructures on thin Si wafers, we are able to reduce the shading loss to zero and enhance carrier collection. The absence of the metallization grid on the front side increases the short- circuit current (Jsc) of the cells dramatically.
BackPEDOT cells with cross-finger type electrodes of different back emitter shading ratios were fabricated and tested. An optimized efficiency of 15.7% was achieved from cells with a shading ratio of 67%. It indicates that, at this particular shading ratio, diffusion lengths and carrier collection efficiency were optimized for both majority and minority carriers. By further increasing the width of Al electrodes from 200 um to 300 um and reducing the pitch between anode and cathode from 200 um to 150 um, the Fill Factor and efficiency of the BackPEDOT solar cells were further improved from 0.54 to 0.6 and from 15.7 % to 17.6%, respectively.
Due to the cross-finger type electrodes employed on the devices, the rear side of the cells is not fully covered by the electrodes, which means that there are still exposed organic-silicon junction areas that can absorb sunlight. An efficiency of 1% was measured when the rear side of the solar cell was under 1.5AM illumination. Therefore, in principle, one can expect a total conversion efficiency of 18.6% when both sides of the cell are illuminated simultaneously.
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