Nanowire Photovoltaic Devices, Phase II

The high-efficiency of the proposed device represents a significant competitive advantage for any space-based power generation application. This proposed device offers a significant increase in efficiency which corresponds to a significant cost savings in terms of photovoltaic array size, array weight, and launch costs. The proposed cells would represent a disruptive technology within the space photovoltaic marketplace. Additionally, a path is proposed for commercial, low-cost nanowire growth with broad market implications. Nanowires of highly mismatched systems (>7%) have been demonstrated in the literature and, more importantly, in the Phase 1 of this proposal. This flexibility in substrate/nanowire combinations enables more optimum bandgap and material combinations for novel devices. One exciting possibility is the integration of III-V nanostructures on low-cost silicon substrates for photovoltaic applications. In addition, the use of core-shell geometry for photovoltaic applications decouples the absorption length from the carrier collection length, which allows low diffusion length material to be effective PV materials in the core-shell configuration. The high efficiency (>40%) of the proposed PV cell will make it the obvious choice for NASA space-based applications. Another potential application revisits a NASA research thrust on virtual substrates. One important aspect of nanowires is the demonstrated capability to integrate widely mismatched nanowires and substrates. The restricted cross-sectional area of the nanowire reduces the opportunity for mismatch defect generation. Nanowires of highly mismatched systems (>7%) have been demonstrated in the literature and, more importantly, in the Phase 1 of this proposal. This flexibility in substrate/nanowire combinations can enable more optimum bandgap and material combinations for novel devices. Incorporating nanowires onto a recrystallized Ge/metal foil substrate would potentially solve the problem of grain boundary shunting of generated carriers by restricting the cross-sectional area of the nanowire (10s of nms diameter) to sizes smaller than the recrystallized grains (0.5-1 um2). In this approach, the nanowire PV device integrated with a low-cost foil substrate would have potential for high weight-specific power (W/kg). More »