| The amorphous silicon/crystalline silicon heterojunction(HAC)solar cells have many outstanding advantages,such as high conversion efficiency,low decay rate and bi-facial power generation,and have the prospect of becoming the next generation of main solar cells.In recent years,it has been reported that the energy efficiency of HAC cells could be enhanced with photo-thermal post-treatment but no further systematic study has been found.In this thesis,we designed and made an LED-based photo-thermal processing device with different wavelengths and adjustable intensities to conduct many experiments of full size HAC cells for further analyzing the phenomena and mechanisms of the process.Based on the understanding,we proposed electro-thermal treatment on HAC cells and also designed and made an experimental device of electro-thermal post-treatment of full size HAC cells for experimental detection.The main results are as following:(1)Four LED modules with a wavelength of blue,green,yellow and red,separately were used to do the photo-thermal post-treatment on HAC cells,All the treatments are beneficial to enhance the performance of the solar cells.In which,the red LED light source is the best.In our research,the higher intensity of the LED light sources,the better enhancement of the cells.By the post-treatment with a most heavy red light soaking 10 mins and heated at 200?,the average conversion efficiency of HAC cells(baseline is 22.8%)can promote about 0.31%and the champion wafer achieves 0.47%for conversion efficiency.It is founded that too much irradiation by blue LED light source would lead to degradation of the enhanced effect.The main reasons of the photo-thermal enhancement are the improvement of the passivation effect which leading to the rise of Voc(open-circuit voltage)and the decrease of series resistance which leading to the rise of FF(fill factor).By referring to the relevant simulation research,we believe that the photons of LED can broke the Si-H configuration in the physical bonding mode and the high temperature can provide additional energy to release the H atoms,which can passivate the defects and interface dangling bonds.In addition,the Si dangling bonds formed after the Si-H release H atoms are prone to recombine at high temperature to form strong Si-Si bonds.As a consequence,the photo-thermal treatment would improve the conversion of efficiency of HAC cells.(2)The conversion efficiency of HAC cells also can be enhanced by electro-thermal post-treatment.In particular,the conversion efficiency of HAC cells with 22.8%basic efficiency will increase about 0.28%(average absolute value)under the condition of DC-50A(direct current)at positive bias and 200? heating temperature for 10mins.And the enhancement of electro-thermal mainly attributes to the promotion of Voc and FF.Too heavy direct current(>100A)will destroy the silver bars,and also the passivation effect.According to the experimental results,DC50-80A is the best choice.At the same time,it is believed that the electrical injection will motivate the H in the amorphous silicon film,especially the Si-H configuration in the physical bonding mode,which can passivate the defects and interface dangling bonds.And the thermal processing is necessary in the process,which is similar to the photo-thermal post-treatment. |
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