Record Infrared Internal Quantum Efficiency in Silicon Heterojunction Solar Cells With Dielectric/Metal Rear Reflectors

Abstract

Inserting a dielectric between the absorber and rear metal electrode of a solar cell increases rear internal reflectance by both limiting the transmission cone and suppressing the plasmonic absorption of light arriving outside of the cone. We fabricate rear reflectors with low-refractive-index magnesium fluoride (MgF 2 ) as the dielectric, and with local electrical contacts through the MgF 2 layer. These MgF 2 /metal reflectors are introduced into amorphous silicon/crystalline silicon heterojunction solar cells in place of the usual transparent conductive oxide/metal reflector. An MgF 2 /Ag reflector yields an average rear internal reflectance of greater than 99.5% and an infrared internal quantum efficiency that exceeds that of the world-record UNSW PERL cell. An MgF 2 /Al reflector performs nearly as well, enabling an efficiency of 21.3% and a short-circuit current density of nearly 38 mA/cm 2 in a silicon heterojunction solar cell without silver or indium tin oxide at the rear.

CH_3NH_3PbI_3 perovskite / silicon tandem solar cells: characterization based optical simulations

“…This thickness results in a similar long-wavelength response as an experimentally measured textured state-of-the-art SHJ cell (symbols in Fig. 3) [35]. With this approach our model has a much lower computation time but the results are comparable to the computationally demanding ray tracing routines.…”

“…In a single-junction design, such cells exhibit high open-circuit voltages (V oc ) of up to 750 mV [33] thanks to high c-Si bulk lifetimes and excellent surface passivation. These cells are particularly well-suited for bottom cell applications from an electrical and optical perspective: Their high voltages are maintained at reduced illumination levels, and with proper light management [34] these cells exhibit excellent external quantum efficiency (EQE) response in the long-wavelength region [35]. Our results are also valid for other types of c-Si solar cells, such as diffused junction cells, as the a-Si layers and diffused regions influence the optical properties only marginally.…”

“…The simulated texture consists of a periodic array of 5-µm-high upright pyramids with a characteristic angle of 54.7°. Since the front surface texture not only reduces reflection, but also increases the optical path length, the optical thickness of the absorber with a textured front surface has to be adjusted to 1.5 mm to yield a good agreement with the longwavelength response of the measured SHJ cell [35]. Note that the optical absorber thickness is still larger than the usual ~100 µm thick SHJ cell absorber.…”

Transparent Electrodes for Efficient Optoelectronics

“…2017, 1600529 www.advancedsciencenews.com Figure 2. a) AM1.5G 1 sun irradiance spectra and b) quantum efficiency of a perovskite, [108] CdTe, [95] CIGS, [95] perovskite-SHJ tandem, [109] and SHJ [110] solar cells as a function of wavelength. The absorptance curve of different transparent electrodes measured on glass is also shown for comparison of the relevant wavelength range to be taken into account when developing transparent electrodes for solar cells.…”

Back-Contacted Silicon Heterojunction Solar Cells With Efficiency >21%

“…These J sc losses are linked to the short-wavelength response of SHJ devices [6]. In the long-wavelength part of the spectrum, wellengineered SHJ devices can outperform the best reported homojunction solar cells [7].…”