Enhanced Diffuse Reflectance of Photons in Molybdenum Back Electrode Films Achieved via Surface Texturing for Thin Film Solar Cells

Abstract

Molybdenum (Mo) thin film is widely used as the bottom electrode in substrate‐configured thin film solar cells due to its high conductivity and reflectivity. Mo grown onto microtextured substrates increases the diffuse reflection of incident photons via scattering/multiple reflections on the corner/edges, in addition to the contribution from increased surface area. Herein, bilayer Mo is grown using direct current magnetron sputtering onto plain and textured substrates. To texture the glass substrate surface, a periodic array of cross‐linked photoresist structures (SU‐8 2000.5 & SU‐8 2005) is introduced via UV‐lithography process. Characterizations are done using X‐ray diffractometer, optical microscope, scanning electron microscope, and optical profilometer. Angle‐dependent specular reflectance, diffuse reflectance, and electrical measurements done on Mo grown on plain and textured substrates lead to a comprehensive understanding of the advantages of growing Mo films on textured substrates. The electrical resistivity of Mo grown on plain and textured substrates is of the same order, measuring 3.09 × 10−5 Ω cm, 3.25 × 10−5 Ω cm, and 3.87 × 10−5 Ω cm, respectively. A high‐diffuse reflectance of 62.7% is obtained for SU‐8 2005 textured Mo films. Investigations using COMSOL simulations support the optical reflectance analysis.