Abstract
Current design addresses a few major issues of efficient harvesting of solar energy, namely, ability of variable energy gap cascaded p-i-i-n a-Si/c-Si structure to absorb wide energy spectra avoiding overheating of the device and increasing the number of sun-hours by 30% with no sun-tracking. The novel solar cell consists of top 0.1μm thick acceptor doped (1016cm-3) a-Si layer followed by 2.5μm of intrinsic a-Si. Next intrinsic region is 2.5μm thick c-Si followed by the 1μm layer donor doped (1016cm-3) c-Si. The i-i layers designed with Egap1=1.97eV and Egap2=1.12eV are the most productive generators of photocarriers due to low rate of recombination. The cascaded design prevents the overheating of c-Si layers, as absorption of high energy photons happens in a-Si layers of the material with Egap1 =1.97eV. In order to improve interaction with sun as it is low above horizon (sun rise/sun set) we designed a corrugation of upper layers of our cascaded solar cell. It is very challenging to texture amorphous Si material on the top of the sell. Therefore we designed sequence of technological steps, where crystalline Si was selectively etched, followed by CVD epitaxy of amorphous layers, replicating the surface configuration of c-Si. The designed solar cell has efficiency of 29.4%, with filling factor of 0.86. The designed corrugated surface of the cell prolongs the sun hours by about 30%.