Cascaded heterostructured a-Si/c-Si solar cell with increased current production

摘要

In this study we present a cascaded solar cell with a heterostructure consisting of p-i-n-n-i-p regions. The detailed structure starts with the bottom layer of 0.01μm thin film p-doped (1017cm-3) c-Si, followed by 0.44μm thick intrinsic (c-Si) layer, covered by 0.1μm thin n-doped (1016cm-3) c-Si. Next floor of the cascaded structure consists of larger energy gap material which is designed to be 0.1μm thin n-doped (1016cm-3) a-Si, covered by 0.44μm thick intrinsic (a-Si) layer and followed at the top by p-doped (1017cm-3) a-Si of 0.01μm thickness. The described monolithic structure could be considered as a multi-junction solar cell with obvious advantages as compared to existing multi-junction solar devices. Most of the thickness of our device is occupied by intrinsic layers, were high generation of electron-hole pairs is not affected by intensive recombination processes. We avoid usage of tunneling interconnects, which do decrease the total current of the solar cell. The potential step at the energy diagram between thin layers of n-type of a-Si and n-type of c-Si is negligible, i.e. the collection of carriers from both p-n junctions through the common electrode is very efficient. In conventional stacked one above the other multi-junction cell the total current is equal to the smallest current of a junction in stack. In our design the two p-i-n structures are adding the currents due to common terminal created for the a-Si/c-Si n-type interface and due to wired together both p regions. The collected densities of current from amorphous cell and for crystalline counterpart are 19.87 mA/ cm2 each. The modeled built-in potential, i.e. open circuit voltage came out somewhat smaller than observed in stacked p-n junctions. In our case it is about 0.52V. However the modeling of this thin-film solar cell demonstrates higher efficiency compared to similar Si heterostructures. The filling factor of designed solar cell is FF= 0.80 and efficiency is 22.2%. The corrugated top of the solar cell increases the number of sun-hours by 30%.