Dopant-Free All-Back-Contact Si Nanohole Solar Cells Using MoO_<i>x</i> and LiF Films

We demonstrate novel all-back-contact Si nanohole solar cells via the simple direct deposition of molybdenum oxide (MoO_<i>x</i>) 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 MoO_<i>x</i> 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 MoO_<i>x</i>/Si interface and suppressed recombination at the Si and LiF/Al electrode interface. With optimized MoO_<i>x</i> and LiF film thickness as well as the all-back-contact design, our 1 cm² Si nanohole solar cells exhibit a power 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 MoO_<i>x</i> and LiF films formed by a simple deposition process presents a unique opportunity to develop highly efficient and low-cost nanostructured Si solar cells