Paths to light trapping in thin film GaAs solar cells

Abstract

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Engineering the reciprocal space for ultrathin GaAs solar cells

“…Therefore, the QR PCs obtain higher performance than the PC counterparts. In contrast, the literature founds less benefits for the GaAs, 20 as the thickness where light trapping could be very beneficial are few hundred nm with a few guided modes available. Furthermore, the proximity of the silver mirror to the ultrathin nanostructured layer creates parasitic absorption in the metal, if it is not mitigated with a dielectric spacer.…”

“…The use of QR PCs has been proposed for Si cells 12,33 and for thin GaAs cells 20 . Si benefits from a thicker substrate (microns instead of hundreds of nm) allowing the light to couple to more guided modes.…”

“…10,[15][16][17][18] A refinement of this approach is to randomize the super-cell while aiming at a target PSD distribution. 12,14,19,20 These techniques heavily rely on the real space distribution, and the optimization algorithm used. Furthermore, these methods are computationally intensive, limiting the study for big unit cells.…”

Improving the Performance of Solar Cells Under Non-Perpendicular Incidence by Photonic Crystal

“…Since the photovoltaic effect was found, the semiconductor solar cells (SCs) have been widely used [3], [4]. With the efforts of scientists and engineers, the photoelectric conversion efficiency (PCE) of SC has progressed a lot [5]- [11]. The PCE of six-junction SCs has reached 47.1% [12].…”

Optimum Luminescent Down-Shifting Properties for High Efficiency and Stable Perovskite Solar Cells

“…However, decreasing thickness leads to lower red-NIR absorption, as this radiation has higher penetration depth. Therefore, different light-trapping (LT) methods have been studied to improve this low-energy absorption, such as the use of metallic or dielectric nanoparticles, [41][42][43] front or rear texturing of the cell 6,44,45 and the use of high index dielectric structures on the cell front. 7,46,47 This latter LT method, operating in the regime of wave-optics, is the one considered in this work.…”