Sandwiching intermediate reflectors in tandem solar cells for improved photon management

Abstract

In tandem solar cells, intermediate reflectors are employed to increase light absorption in the top cell. Thus far, the use of photonic crystals for this purpose was not optimal since side-lobes in the reflection spectrum reduced the absorption in the bottom cell. To compensate this reduction, the bottom cell thickness had to be excessively increased; nullifying the main advantage of thin-film solar cells. Here, we suggest to solve this issue by reducing the impedance mismatch between photonic crystal and bottom cell using anti-reflection layers. The concept is even validated for solar cells comprising random textures.

Pyramidal surface textures for light trapping and antireflection in perovskite-on-silicon tandem solar cells

“…Thus, a wavelength-selective intermediate reflector is required to maximize the light-trapping benefits of a textured surface. A large body of work has been published on light-trapping in micromorph Si cells (a thin-film tandem of α-Si:H and µc-Si:H), which are typically deposited onto textured substrates with sub-wavelength features [13][14][15][16][17][18]. Combining a selective intermediate reflector (IR) with these surfaces can provide significant light-trapping in the top cell.…”

“…Combining a selective intermediate reflector (IR) with these surfaces can provide significant light-trapping in the top cell. Various types of IRs have been studied, including 1D, 2D and 3D photonic crystals [15][16][17][18][19] and metallic nanoparticles [14].…”

Detailed-balance efficiency limits of two-terminal perovskite/silicon tandem solar cells with planar and Lambertian spectral splitters

“…Earlier, spectral splitting in 4T tandem cells has been modeled, 19 and it was predicted that, by integrating a spectral splitting light trapping layer, an efficiency gain between 0.5% and 3% (absolute) and a two-to threefold reduction in thickness of the top cell can be reached, depending on the diffusion length of the absorber material. The benefits of spectral splitting in 2T tandem concepts have been studied previously to achieve current matching between top and bottom cells, using Bragg reflectors [22][23][24][25] or three-dimensional photonic crystals [26][27][28] as intermediate layers, and small spectrum splitting improvements for Si-based top and bottom cells could be shown. Current matching is a limiting factor in 2T perovskite/Si tandems for perovskites with a bandgap below E BG ¼ 1.73 eV.…”

Photonic Intermediate Structures for Perovskite/c-Silicon Four Terminal Tandem Solar Cells

“…Photon management can be achieved by placing intermediate photonic reflectors between the two cells, with the reflectance designed to match the top cell absorption band. Examples of intermediate reflectors include homogeneous layers [15,16], photonic crystals [15][16][17][18], metallic nanoparticles [19], stacked layers [15,16] and a combination of those with randomly texturized surfaces [20]. It is interesting to note that most of the attention has been paid to the reflectance at shorter wavelengths, motivated by the desire to optimise the top cell performance [15][16][17][18][19][20], with only a few papers addressing the problem of optical impedance matching into the lower cell [18].…”