10-Fold-Stack Multilayer-Grown Nanomembrane GaAs Solar Cells

Abstract

Multilayer-grown nanomembrane GaAs represents an enabling materials platform for cost-efficient III−V photovoltaics. Herein we present for the first time 10-foldstack ultrathin (emitter + base: 300 nm) GaAs solar cells. Photovoltaic performance of 10-fold-stack GaAs solar cells exhibited promising uniformity, with only slight efficiency degradation, where comparatively poor short-wavelength response was mainly responsible for the slightly reduced performance in early grown materials. Secondary ion mass spectrometry revealed the concentration of p-type dopant has been changed due to the out-diffusion of beryllium, while the extent of diffusion increasingly diminished in early grown stacks because of the reduced concentration gradient as well as the decrease of beryllium diffusivity at longer annealing times. It is therefore concluded that the performance degradation in 10-fold-stack GaAs solar cells does not develop continuously throughout the growth, but instead becomes spontaneously saturated at longer growth times, providing promising outlook for the practical application of multilayer epitaxy toward cost-competitive GaAs solar cells.

Plasmonically Enhanced Spectral Upconversion for Improved Performance of GaAs Solar Cells under Nonconcentrated Solar Illumination

“…Such an increase of η ext upon printing means more efficient photon recycling that can lead to greater quasi-Fermi level splitting and thus increase of V oc . 4,30,32 The corresponding reverse-bias saturation current (I 0 ) obtained from fitting the dark IV data using a single-diode equation 33 (Figure S3 and Table S1) decreased from ∼4.7 × 10 −13 A (on wafer) to ∼3.0 × 10 −13 A (printed on plain Ag), thereby supporting this analysis. On the other hand, when the bottom contact layer was completely removed by wet chemical etching (green line in Figure 4), the long wavelength light that was not absorbed and reflected either at the rear surface of the solar cell or by the underlying silver reflector can readily reach to the base for reabsorption without parasitic losses, which results in the substantial enhancement of both J sc and V oc .…”

“…This enhancement of V oc is attributed to the effect of a low index medium below the printed solar cell and resultant increase of external luminescence efficiency (η ext ) for the emitted photons through the front surface of the cell, consistent with the following expression of V oc , , where V db , k , T , q , and J 0 are open-circuit voltage for the detailed balance limit, Boltzmann’s constant, absolute temperature, electronic charge, and reverse-bias saturation (or dark) current density, respectively. Such an increase of η ext upon printing means more efficient photon recycling that can lead to greater quasi-Fermi level splitting and thus increase of V oc . ,, The corresponding reverse-bias saturation current ( I 0 ) obtained from fitting the dark IV data using a single-diode equation (Figure S3 and Table S1) decreased from ∼4.7 × 10 –13 A (on wafer) to ∼3.0 × 10 –13 A (printed on plain Ag), thereby supporting this analysis. On the other hand, when the bottom contact layer was completely removed by wet chemical etching (green line in Figure ), the long wavelength light that was not absorbed and reflected either at the rear surface of the solar cell or by the underlying silver reflector can readily reach to the base for reabsorption without parasitic losses, which results in the substantial enhancement of both J sc and V oc .…”

Strain-Engineered Multilayer Epitaxial Lift-Off for Cost-Efficient III–V Photovoltaics and Optoelectronics

“…Substrate reuse techniques, such as epitaxial lift-off (ELO) − and controlled spalling, − have been developed to reduce the costs. Of these, ELO has been identified as the most cost-efficient approach, also having the advantage of large-scale applicability. , The resulting thin-film devices have additional inherent advantages such as flexibility and ultra-lightweight. ,− The combination of high solar conversion efficiency, lightweight, and flexibility make these thin-film cells highly attractive for a number of application areas including space, electric vehicles, drones, military, and the Internet of things.…”

CuI as a Hole-Selective Contact for GaAs Solar Cells

“…In multijunction tandem solar cells, nearly 50% conversion efficiencies have been achieved with III–V semiconductors . In addition, they have high absorption in the solar spectrum, enabling the fabrication of ultrathin, ultralight, and flexible devices − that are in demand in application areas such as internet of things, integrated devices on curved surfaces, drones, and satellites. As such, although III–V semiconductors are of great interest and importance for solar cells, their fabrication complexity and high cost remain bottlenecks for their widespread use.…”