Abstract
Intermediate band solar cells (IBSCs) are conceptual and promising for next generation high efficiency photovoltaic devices, whereas, IB impact on the cell performance is still marginal due to the weak absorption of IB states. Here a rational design of a hybrid structure composed of ZnTe:O/ZnO core-shell nanowires (NWs) with Al bowtie nanoantennas is demonstrated to exhibit strong ability in tuning and enhancing broadband light response. The optimized nanowire dimensions enable absorption enhancement by engineering leaky-mode dielectric resonances. It maximizes the overlap of the absorption spectrum and the optical transitions in ZnTe:O intermediate-band (IB) photovoltaic materials, as verified by the enhanced photoresponse especially for IB states in an individual nanowire device. Furthermore, by integrating Al bowtie antennas, the enhanced exciton-plasmon coupling enables the notable improvement in the absorption of ZnTe:O/ZnO core-shell single NW, which was demonstrated by the profound enhancement of photoluminescence and resonant Raman scattering. The marriage of dielectric and metallic resonance effects in subwavelength-scale nanowires opens up new avenues for overcoming the poor absorption of sub-gap photons by IB states in ZnTe:O to achieve high-efficiency IBSCs.
Highlights
Thanks to the strong light-matter interaction, one dimensional semiconductor nanowires (NWs) have opened new avenues in photonics and solar energy harvesting, and provided an extraordinary platform for nano-optoelectronic applications, including lasers, optical switches[1], photodetectors[2] and solar cells[3]
Oxygen-doped ZnTe (ZnTe:O) exhibits a distinct sub-bandgap emission and photoresponse around 1.8 eV due to oxygen-bounded excitonic absorption[9, 10]. It has been regarded as one of promising materials for intermediate band solar cells which can enable the absorption of low energy photons and reach a detailed balance efficiency limits of 63.2% in theory[11, 12]
The dimension of ZnTe:O/ZnO core/shell NWs are numerically optimized to form the dielectric resonance of leaky modes in visible spectrum region, maximizing the overlap between the optical absorption in ZnTe:O and the solar spectrum
Summary
Thanks to the strong light-matter interaction, one dimensional semiconductor nanowires (NWs) have opened new avenues in photonics and solar energy harvesting, and provided an extraordinary platform for nano-optoelectronic applications, including lasers, optical switches[1], photodetectors[2] and solar cells[3]. The lack of sufficient light absorption in single NWs due to its small absorption volume remains challenging for developing efficient concentrated NW solar cells[14] In this contribution, we exploit the highly confined dielectric resonance in NWs and plasmonic coupling with integrated bowtie nanoantennas to improve light trapping and boost the broadband absorption of ZnTe:O/ ZnO core/shell NWs. The dimension of ZnTe:O/ZnO core/shell NWs are numerically optimized to form the dielectric resonance of leaky modes in visible spectrum region, maximizing the overlap between the optical absorption in ZnTe:O and the solar spectrum. The non-traditional plasmonic metal, aluminum (Al) is chosen as the antenna material due to its complementary metal-oxide-semiconductor (CMOS) compatibility, low-cost, sustainability, and mass-productivity[15] Both theoretical simulation and experimental results are well consistent that, with integration of Al plasmonic bowtie antenna around the ZnTe:O/ZnO core/shell NW, efficient resonant coupling between surface plasmons and dielectric nanowire leads to further enhancement in absorption and radiative emission, for the broadband near 680 nm. If the NW length satisfies certain conditions, longitudinal-field Fabry-Perot (F-P) resonance will be generated and leads to hybrid modes through interaction with transverse radial resonances[20]
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