Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

Abstract

This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al0.52In0.48P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF2/ZnS anti-reflective coating demonstrated open-circuit voltages (Voc) up to 1.00 V, short-circuit current densities (Jsc) up to 24.5 mA/cm2, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated Jsc and conversion efficiency of these devices are expected to reach 26.6 mA/cm2 and 20.7%, respectively.

The Design and Optimization of GaAs Single Solar Cells Using the Genetic Algorithm and Silvaco ATLAS

“…Moreover, a comparison between the optimized and the initial solar cells can be observed in Figure 10, as well as results comparison with corresponding theoretical and experimental results for similar studies. Our GA-proposed simulation gives good result with high-efficient performance than others introduced in various previous studies as discussed elsewhere [14][15][16][17]. Differences are due to the variations in the material, optical parameters used, and optimization performance method presented in this work.…”

Reflective Barrier Optimization in Ultrathin Single-Junction GaAs Solar Cell

“…The intraband nonradiative scattering is included through electron-phonon interactions. Into thin layers the impact of the CB-VB nonradiative scattering is expected to be weak [3]. At the interfaces and contacts, the recombination rate can be larger, but it highly depends on growth conditions.…”

“…Table I shows the corresponding short-circuit current I sc , open-circuit voltage V oc , fill factor (FF), and maximal generated power P max . Inspired by devices of [3] and in order to have fair comparisons, all modeled cells are 220 nm thick, which includes window, undoped GaAs absorber, and BSF. Absorption of photon and then carrier generation are possible in all these layers.…”

“…A good selectivity requires large dop- ing concentration in barriers. However, in order to be realistic, we considered doping used in [3]. This experimental work considers the same thickness of 30 nm for the two barriers.…”

“…In order to still increase the efficiency and also to reduce material consumption and cost, ultrathin solar cells propose to absorb light efficiently within a few hundreds of nanometers (<300 nm). In these devices, both light management [2], [3] and recycling of photons generated by radiative recombination [4], [5] are necessary to maximize the absorption. Concerning the electronic transport, in thin-film solar cells, GaAs absorber is sandwiched between two high-bandgap lattice-matched layers of In 0.49 Ga 0.51 P or Al x Ga 1−x As to reflect the minority carriers [6].…”