Advanced microhole arrays for light trapping in thin film silicon solar cells

We present a comprehensive theoretical analysis accompanying our experimental development of micro-structured thin film polycrystalline silicon solar cell absorbers. Our focus is on 2D-periodic arrays of holes which do not act as a superficial scattering grating but pierce the entire silicon absorber layer. We deviate from the commonly used model of vertical hole sidewalls by employing conical frustum shaped holes with a range of opening angles. Additionally, an experimentally motivated front texture is applied to the simulated solar cell absorbers and varied in texture aspect. Based on this parametric absorber model, for a single domain period of 2 pm, we discuss light trapping and optical losses in thin film cells with absorptive front and back contacts and a perfectly transparent glass encapsulation layer. Implications from this study are that light trapping in square periodic arrays with periods larger than the wavelength of light can be enhanced by microholes but that it cannot replace a front texture which provides both antireflection and scattering. (C) 2013 Elsevier B.V. All rights reserved.