Processing and characterization of large area InP nanowire photovoltaic devices

Abstract

III−V nanowire (NW) photovoltaic devices promise high efficiencies at reduced materials usage. However, research has so far focused on small devices, mostly ≤ 1 mm². In this study, the upscaling potential of axial junction InP NW photovoltaic devices is investigated. Device processing was carried out on a full 2” wafer, with device sizes up to 1 cm², which is a significant increase from the mm-scale III−V NW photovoltaic devices published previously. The short-circuit current density of the largest 1 cm² devices, in which 460 million NWs are contacted in parallel, is on par with smaller devices. This enables a record power generation of 6.0 mW under AM1.5G llumination, more than one order of magnitude higher than previous III−V NW photovoltaic devices. On the other hand, the fill factor of the larger devices is lower in comparison with smaller devices, which affects the device efficiency. By use of electroluminescence mapping, resistive losses in the indium tin oxide (ITO) front contact are found to limit the fill factor of the large devices. We use combined light-beam induced current (LBIC) and photoluminescence (PL) mapping as a powerful characterization tool for NW photovoltaic devices. From the LBIC and PL maps, local defects can be identified on the fully processed devices.

Vertically Processed GaInP/InP Tandem-Junction Nanowire Solar Cells

“…Under exposure to the scanning electron beam, a photocurrent of 0.03 nA is generated, which corresponds to 14 mA/cm 2 if multiplied with the density of the NWs in the array, 460 million NWs per cm 2 . 31 The single-NW open-circuit voltage is measured to be V OC = 1.7 V, a result of voltage addition from the GaInP and InP subcells, thus confirming the intended functionality of the tandem-junction device. For samples with higher Ga content x in the Ga x In 1– x P top cell and, thus, higher GaInP band gap, an increase in V OC is measured, reaching up to V OC = 2.45 V for x = 0.69 as seen in Figure S4 .…”

“…Under exposure to the scanning electron beam, a photocurrent of 0.03 nA is generated, which corresponds to 14 mA/cm 2 if multiplied with the density of the NWs in the array, 460 million NWs per cm 2 . The single-NW open-circuit voltage is measured to be V OC = 1.7 V, a result of voltage addition from the GaInP and InP subcells, thus confirming the intended functionality of the tandem-junction device.…”

“…The NW arrays were processed in an analogous manner to InP NW photovoltaic devices, described in more detail in other publications and illustrated schematically in Figures S2 and S3. , The processing steps include atomic layer deposition of SiO x , planarization using Cyclotene 3022-46 (BCB), and reactive ion etching (RIE) of excessive BCB and SiO x covering the Au particles at the NW tips. The Au particles were wet-etched and the NW tips contacted using a 150 nm-thick sputter-coated indium tin oxide (ITO) film as a transparent front contact.…”

Absorption of Light in Vertical III-V Semiconductor Nanowires for Solar Cell and Photodetector Applications

“…In large-area nanowire arrays, varying types of imperfections, including missing nanowires and electrical contacting issues of some nanowires are possible [73]. Characterization of such effects then becomes important [73]. In optics simulations, we have seen that neighboring nanowires can efficiently compensate in absorption for a missing nanowire [74].…”

“…In large-area nanowire arrays, varying types of imperfections, including missing nanowires and electrical contacting issues of some nanowires are possible [73]. Characterization of such effects then becomes important [73].…”