Highly transparent modulated surface textured front electrodes for high‐efficiency multijunction thin‐film silicon solar cells

Abstract

To further increase the efficiency of multijunction thin-film silicon (TF-Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high-quality silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light-trapping structures in multijunction TF-Si solar cells. The MST substrates comprise a micro-textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub-micron nano-textured ZnO layer grown by low-pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in-coupling and light trapping for the top amorphous silicon (a-Si:H) solar cell while minimizing the parasitic absorption losses. The crater-shaped micro-textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high-quality nanocrystalline silicon (nc-Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high-quality silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single-textured state-of-the-art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a-Si:H/nc-Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state-of-the-art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high-efficiency multijunction solar cells.

Comparison of Light Trapping in Silicon Nanowire and Surface Textured Thin-Film Solar Cells

“…The nanotextured contact layers reduce reflection losses and enhance the scattering and diffraction of light within the solar cells. Moreover, the optical path length is increased leading to an enhanced quantum efficiency and short circuit current density in the red and infrared range of the optical spectrum (wavelengths between 600 and 1100 nm) [6][7][8][9]. Furthermore, alternative approaches, such as 3D solar cells [10][11][12][13][14][15] or nanowire solar cells, have gained considerable attention in recent years [16][17][18][19][20].…”

“…Experimentally, high conversion efficiencies have been achieved by texturing the contact layers of silicon solar cells [2][3][4][5][6][7][8][9]. The nanotextured contact layers reduce reflection losses and enhance the scattering and diffraction of light within the solar cells.…”

Artifact Interpretation of Spectral Response Measurements on Two‐Terminal Multijunction Solar Cells

“…When the difference between the dJ/dV of the two subcells decreases, the probed EQE deviates more from the genuine EQE of the bottom subcell. The The gray dashed curves show the genuine EQE spectra of the top and bottom subcells, [27] and the vertical dashed-dotted lines indicate the two wavelengths at which the cell operation is further discussed. b) Left axis, circle marker: the probed EQE at certain wavelengths.…”

Photonic Structures for Light Trapping in Thin Film Silicon Solar Cells: Design and Experiment

“…For n-i-p TFSCs, light-trapping primarily occurs owing to the textured back reflector. In the last few years, a variety of novel light-trapping concepts and structures, including low pressure chemical vapor deposited (LPCVD) -ZnO [14], chemically-etched ZnO [15], textured glass [13], modulated surface textures [16], plasmonic light-trapping [17,18], honeycomb pattern substrates [19] and photonic structures [20][21][22][23][24][25][26][27][28][29][30][31], have been widely studied and utilized to improve the solar cell performances. Recently, a dielectric one-dimensional photonic crystal (1D-PC), which is formed by periodically stacking high refractive index (high-n) layers and low refractive index (low-n) layers [25][26][27], also was regarded as a highly promising light-trapping concept.…”

“…For TFSCs, one of the most effective approaches to achieve high performance is to devise a state-of-the-art light harvesting system including in-coupling sufficient light into the solar cells via the front surface (namely light coupling) [8][9][10] and efficiently trapping the incoming light in the thin absorption layers (namely light-trapping) [11][12][13]. For n-i-p TFSCs, light-trapping primarily occurs owing to the textured back reflector.…”