Numerical simulation of innovative device structures for silicon thin-film solar cells

We investigate the optical and electronic properties of thin-film silicon solar cells by means of numerical simulations. The optical design under investigation is the encapsulated-V texture which is capable of absorbing sunlight corresponding to a maximum short circuit current density of 35 mA/cm². Since the layer thickness can be restricted to only 4 μm, the encapsulated-V structure provides also a good collection efficiency for photogenerated charge carriers. Practical efficiencies around 12% can be expected for Si material with a minority carrier lifetime as low as 10 ns. Increased lifetimes of 100 ns allow for about 14% efficiency. The benefit of multiple junctions strongly depends on surface recombination. The efficiency of a single junction cell can be improved from 10% to 13% by a three junction device if the surface recombination velocity is as high as 10⁵ cm/s. For moderate surface recombination the gain is only 1%