Dopant-free All-back-contact Si Nanohole Solar Cells using MoOx and LiF Films

Abstract

We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoOx) and lithium fluoride (LiF) thin films as dopant-free and selective carrier contacts (SCCs). This approach is in contrast to conventionally used high-temperature thermal doping processes, which require multistep patterning processes to produce diffusion masks. Both MoOx and LiF thin films are inserted between the Si absorber and Al electrodes interdigitatedly at the rear cell surfaces, facilitating effective carrier collection at the MoOx/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoOx and LiF film thickness as well as the all-back-contact design, our 1-cm2 Si nanohole solar cells exhibit a conversion efficiency of up to 15.4 %, with an open-circuit voltage of 561 mV and a fill factor of 74.6 %. In particular, because of the significant reduction in Auger/surface recombination as well as the excellent Si-nanohole light absorption, our solar cells exhibit an external quantum efficiency of 83.4 % for short-wavelength light (~400 nm), resulting in a dramatic improvement (54.6%) in the short-circuit current density (36.8 mA/cm2) compared to that of a planar cell (23.8 mA/cm2). Hence, our all-back-contact design using MoOx and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost Si nanostructured solar cells.