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

• We model thin film solar cell optics in 3D using rigorous finite element analysis.
• We include encapsulation light trapping effects by incoherent domain coupling.
• We study absorptance of conical frustum shape microholes with a front texture.
• Front texturing boosts light trapping. Microholes can provide additional scattering.
• Parasitic absorption in contacts is strongly linked to silicon light trapping.

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 2μm, 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.