Photovoltaic (PV) technologies now attract more and more attentions due to the global warming and air pollutions. As second generation solar cells, Si Based thin film solar cells such as a-Si thin film and micromorph structure have been developed for decades and many enhancements have been achieved. Yet they are still suffering the issue of the performance degradation, which is caused by Staebler-Wronski effect. To overcome this matter, as candidates, poly-Si and c-Si thin film materials have been investigated to achieve the higher conversion efficiency with the stable reliability due to the higher material quality.

In this work a novel structure of ultra-thin a-Si/c-Si tandem solar cells on low temperature glass is proposed. The efficiency of 13.4% is obtained which is higher than t...[ Read more ]

Photovoltaic (PV) technologies now attract more and more attentions due to the global warming and air pollutions. As second generation solar cells, Si Based thin film solar cells such as a-Si thin film and micromorph structure have been developed for decades and many enhancements have been achieved. Yet they are still suffering the issue of the performance degradation, which is caused by Staebler-Wronski effect. To overcome this matter, as candidates, poly-Si and c-Si thin film materials have been investigated to achieve the higher conversion efficiency with the stable reliability due to the higher material quality.

In this work a novel structure of ultra-thin a-Si/c-Si tandem solar cells on low temperature glass is proposed. The efficiency of 13.4% is obtained which is higher than the records of a-Si and micromorph solar cells. First, the efficiency of 10.3% is obtained by the heterojunction c-Si thin film bottom cells on glass substrate, which is fabricated by the advanced anodic bonding technology. And since the current limitation comes from the a-Si thin film top cells, a nanoscale inverted pyramid light trapping structure, which is fabricated by the nano imprinting technique, is developed and applied in PV model applications for the first time by our group, and up to 22% current density improvement has been obtained. To further increase the current, which is generated by the top cell, and reduce the voltage loss, which is widely observed on the cells with the rough surface, P type μc-SiO_x is introduced in our design as window layer.

The influence of the hydrogen content in the crystalline precursor a-Si during poly-Si film thermal crystallization is investigated though mircostructure factor R and hydrogen content C_H. However, it is found that poly-Si crystallized from a-Si still has to face different limitations no matter how the hydrogen status have been adjusted in the a-Si films. In this case, we develop a new strategy to directly deposit a high quality poly-Si film and it is bond on low temperature glass. By doing so, the substrate cost can be reduced. Another advantage is the usage of Al back contact, compare to traditional heavily doped poly-Si electrode the low series resistance is provided. So far the efficiency of 4.04% is obtained. Finally, a novel nanoscale pyramid light trapping structure is developed to further increase light absorption for poly-Si thin film solar cells. And as high as 28% light absorb enhancement has been observed.