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

Filter-Free Image Sensor Pixels Comprising Silicon Nanowires with Selective Color Absorption

The organic dye filters of conventional color image sensors achieve the red/green/blue response needed for color imaging, but have disadvantages related to durability, low absorption coefficient, and fabrication complexity. Here, we report a new paradigm for color imaging based on all-silicon nanowire devices and no filters. We fabricate pixels consisting of vertical silicon nanowires with integrated photodetectors, demonstrate that their spectral sensitivities are governed by nanowire radius, and perform color imaging. Our approach is conceptually different from filter-based methods, as absorbed light is converted to photocurrent, ultimately presenting the opportunity for very high photon efficiency

Si Microwire Solar Cells: Improved Efficiency with a Conformal SiO₂ Layer

Silicon microwire arrays have attracted considerable attention recently due to the opportunity they present as highly efficient and cost-effective solar cells. In this study, we report on efficient Si microwire array solar cells with areas of 1 cm² and Air Mass 1.5 Global conversion efficiencies of up to 10.6%. These solar cells show an open-circuit voltage of 0.56 V, a short-circuit current density of 25.2 mA/cm², and a fill factor of 75.2%, with a silicon absorption region that is only 25 μm thick. In particular, the maximum overall efficiency of the champion device is improved from 8.71% to 10.6% by conformally coating the wires with a 200 nm thick SiO₂ layer. Optical measurements reveal that the layer reduces reflection significantly over the entire visible range

Epitaxially Integrating Ferromagnetic Fe_1.3Ge Nanowire Arrays on Few-Layer Graphene

We report vertical growth of ferromagnetic and metallic Fe_1.3Ge nanowire (NW) arrays on few-layer graphene in a large area, induced by a relatively good epitaxial lattice match. Integrating well-aligned NW arrays onto graphene would offer a good opportunity to combine superb material properties of graphene with versatile properties of NWs into novel applications. Fe_1.3Ge NWs are also synthesized on highly ordered pyrolytic graphite (HOPG). Fe_1.3Ge NWs on graphene and HOPG show quite efficient field emission, which are ascribed to the well-interfaced vertical growth, a pointed tip, and high field-enhancement factor (β) of the NWs. The development of ferromagnetic metal NW−graphene hybrid structures would provide an important possibility to develop graphene-based spintronic, electronic, and optoelectronic devices