Optimal-Enhanced Solar Cell Ultra-thinning with Broadband Nanophotonic Light Capture

Abstract

SummaryRecent trends in photovoltaics demand ever-thin solar cells to allow deployment in consumer-oriented products requiring low-cost and mechanically flexible devices. For this, nanophotonic elements in the wave-optics regime are highly promising, as they capture and trap light in the cells' absorber, enabling its thickness reduction while improving its efficiency. Here, novel wavelength-sized photonic structures were computationally optimized toward maximum broadband light absorption. Thin-film silicon cells were the test bed to determine the best performing parameters and study their optical effects. Pronounced photocurrent enhancements, up to 37%, 27%, and 48%, respectively, in ultra-thin (100- and 300-nm-thick) amorphous, and thin (1.5-μm) crystalline silicon cells are demonstrated with honeycomb arrays of semi-spheroidal dome or void-like elements patterned on the cells' front. Also importantly, key advantages in the electrical performance are anticipated, since the photonic nano/micro-nanostructures do not increase the cell roughness, therefore not contributing to recombination, which is a crucial drawback in state-of-the-art light-trapping approaches.

Photonic-structured TCO front contacts yielding optical and electrically enhanced thin-film solar cells

“…The These wavelength-sized pyramidal microstructures can exhibit strong anti-reflection and light scattering effects at the cells' front, as described in previous theoretical studies 11,12 , such optical effects are maximized when the base of the pyramidal features is directly attached to the high-index Si absorber medium. Nevertheless, as observed in previous experimental tests 16 , such optically-optimum case does not allow an electrically-effective front contact, which can only be realized with an additional flat IZO layer deposited prior to the patterning of the microstructured IZO.…”

“…Here the gain in broadband light absorption in a-Si is highest, leading to a quite remarkable photocurrent enhancement value in comparison with the current state-of-art of photonic-enhanced a-Si SCs. 12,21 For the thicker IZO layers, effect 2) is less dominant, so the enhancement curves present a local peak at 190 nm thickness due to the second maximum of the ARC effect 1).…”

“…Therefore, if their response is not omnidirectional, a JSC reduction in one portion of the active area can cause an overall drop in the total current supplied by the cells. In view of this, it is advantageous to implement LT structures able to provide JSC values as high and independent as possible of the incidence angle 12,22 . Such aspect is especially relevant for the ultra-thin a-Si TFSCs, as they can be much more flexible than those with thicker absorbers such as c-Si wafer-based cells.…”

“…High refractive index (n) particles and structures with wavelength-scale dimensions have been considered the preferable light trapping (LT) solutions for integration in the illuminated face of the PV devices, 3,9,10,4 due to their remarkable ability for light in-coupling (anti-reflection) plus scattering towards the absorber medium. Recent theoretical works 11,12 have demonstrated that up to ~50% current enhancement is possible in TF Si cells using arrays of TiO2 (n=2.5-2.7) pyramidal-like microstructured features patterned on the cells' front. This optimized TiO2based LT geometry has been engineered by the authors, via a low-cost colloidal lithography (CL) procedure, and optically-tested on a-Si:H thin film absorbers which allowed the demonstration of pronounced broadband absorption enhancement (27.3% on spectral average) in the Si medium.…”

All-Thin-Film Perovskite/C–Si Four-Terminal Tandems: Interlayer and Intermediate Contacts Optimization

“…These correspond to the maximum LT enhancements that can be achieved and analytically determined within the conceptual regime of ray optics. [28][29][30] Integrating the solar spectrum in the 700-1100 nm range (i.e. the intended absorption region for the bottom cell), the maximum Jph is found to be 233.3 A/m 2 .…”