Homojunction GaAs solar cells grown by close space vapor transport

Abstract

We report on the first pn junction solar cells grown by homoepitaxy of GaAs using close space vapor transport (CSVT). Cells were grown both on commercial wafer substrates and on a CSVT absorber film, and had efficiencies reaching 8.1%, open circuit voltages reaching 909 mV, and internal quantum efficiency of 90%. The performance of these cells is partly limited by the electron diffusion lengths in the wafer substrates, as evidenced by the improved peak internal quantum efficiency in devices fabricated on a CSVT absorber film. Unoptimized highly-doped n-type emitters also limit the photocurrent, indicating that thinner emitters with reduced doping, and ultimately wider band gap window or surface passivation layers, are required to increase the efficiency. Index Terms -semiconductor epitaxial layers, photovoltaic cells, gallium arsenide, III-V semiconductor materials, pn junctions

Analysis of performance-limiting defects in pn junction GaAs solar cells grown by water-mediated close-spaced vapor transport epitaxy

“…We have reported that the electronic properties of GaAs grown by CSVT using H 2 O transport are satisfactory for high-efficiency PV devices, and have demonstrated the first working homojunction GaAs solar cells [19][20][21][22]. Here, we report on progress towards high-efficiency CSVT GaAs solar cells.…”

Low-Cost Approaches to III–V Semiconductor Growth for Photovoltaic Applications

“…Initial devices used a VGF wafer absorber, enabling characterization of CSVT-grown emitters compared to a fixed absorber quality; these devices reached V OC > 900 mV. 84 Despite the high growth temperatures, cross-diffusion was limited, and dopant profiles were similarly abrupt to those grown by the Ptak group using HVPE, occurring over ∼20 nm. 85 Work on solar cells grown entirely by CSVT yielded improved devices, the best having J SC = 13.9 mA cm −2 , V OC = 916 mV, ff = 75%, and η = 9.5% for an unpassivated device with no AR coating (Figure 3E).…”

“…This demonstration of controlled doping and models showing that L D = 1.5 μm could enable η > 20% for a p absorber and n + emitter with an ideal AR coating encouraged us to begin fabricating the first homojunction GaAs devices using H 2 O-CSVT. Initial devices used a VGF wafer absorber, enabling characterization of CSVT-grown emitters compared to a fixed absorber quality; these devices reached V OC > 900 mV . Despite the high growth temperatures, cross-diffusion was limited, and dopant profiles were similarly abrupt to those grown by the Ptak group using HVPE, occurring over ∼20 nm .…”

Selective Area Epitaxy of GaAs Microstructures by Close-Spaced Vapor Transport for Solar Energy Conversion Applications

“…A Te-doped n -GaAs wafer was used as a source for CSVT growth. A custom reactor (described in detail elsewhere) − with two independent heaters to hold the source and substrate wafers (separated by a 1 mm quartz spacer) was filled with H 2 O diluted in H 2 to a total pressure of 1 atm to drive the transport reaction in Figure .…”

“…The microstructure samples were fabricated into photoelectrodes. − A nonaqueous ferrocene/ferrocenium electrolyte was used to make a conformal contact to the microstructure array, allowing for the direct measurement of ensemble current-potential ( J – E ) and impedance characteristics. Average short-circuit currents ( J SC ), open-circuit potentials ( V OC ), and dopant densities ( N D , calculated from Mott–Schottky analysis) are given in Table S2.…”