Experimental demonstration of enhanced photon recycling in angle-restricted GaAs solar cells

Abstract

For cells near the radiative limit, optically limiting the angles of emitted light causes emitted photons to be recycled back to the cell, leading to enhancement in voltage and efficiency. While this has been understood theoretically for some time, only recently have GaAs cells reached sufficient quality for the effect to be experimentally observed.Here, as proof of concept, we demonstrate enhanced photon recycling and open-circuit voltage (V oc ) experimentally using a narrow band dielectric multilayer angle restrictor on a high quality GaAs cell. With angle restriction we observe a clear decrease in the radiative dark current, which is consistent with the observed V oc increase. Furthermore, we observe larger V oc enhancements for cells that are closer to the radiative limit, and that more closely coupling the angle restrictor to the cell leads to greater V oc gains, emphasizing the optical nature of the effect.

Impact of photon recycling and luminescence coupling in III-V photovoltaic devices

“…Influence of Front-Side Angular Selective Filter A front-side angular selective filter, developed & described in [29], is applied to the previous two devices without substrates (base layers of 3.5 and 2.35 m) to explore the influence of higher external radiative efficiency on the V oc [5]. Experimentally, an increase in V oc of 1-2 mV is observed for these two cells after correcting for any increase in photocurrent.…”

“…Otherwise, devices composed of low quality material will be limited by non-radiative recombination processes. Exploiting the photon recycling effect even further using a front side angular selective filter to reduce front side losses has also been shown experimentally to positively influence the V oc by up to 4 mV [5,7]. The contributions to the V oc due to the aforementioned factors except for the latter has so far been explored mostly from a modeling standpoint [6], which lacked experimental validation.…”

“…adiatively dominated solar cells such as those composed of GaAs have recently shown tremendous potential in exploring the influence of light management techniques on device performance, most notably on the open circuit voltage (V oc ) of cells which had the substrate removed [1][2][3][4][5][6]. It is known that thinning the active material of a solar cell reduces the volume within which both radiative and non-radiative recombination occurs.…”

The role of photonics in energy

“…Besides light trapping, for semiconductor materials with fast radiative recombination rates [high internal quantum efficiencies (QEs)], such as GaAs, photon recycling by means of highly reflective back electrodes and controlling interference effects within the active layer have enabled record single-junction solar cell PCEs. 26,142,143 With the development of thin-film optoelectronic devices that have active layer thicknesses below the diffraction limit (i.e., < ∼300 nm); such as small molecule and polymeric OPVs in which the active light harvesting layer thickness ranges from ∼10 to 40 nm and up to ∼250 nm, respectively, light-management techniques using nanophotonic structures, particularly metallic plasmonic structures, have emerged. [144][145][146][147][148][149][150][151][152][153][154][155][156] Metal nanoparticles and structured metallic thin films can localize incident light to subwavelength dimensions due to the excitation of surface plasmons-collective electron oscillations of the free electrons at the surface of metals.…”

Enhanced Photon Collection in Luminescent Solar Concentrators with Distributed Bragg Reflectors

“…The reflected waves at each layer boundary can interfere constructively, creating high reflectance for a certain wavelength range, the so-called photonic stopband. These photonic structures have been used as band-stop filters directly on solar cells 36 and LSCs 37−40 to selectively reflect photons within the escape cone and to achieve enhanced photon recycling. In a recent report from our group, we described an LSC design utilizing core−shell quantum dots combined with a photonic mirror that reflects the entire narrow emission band at nearly all angles, achieving a concentration ratio exceeding 30 for blue photons.…”