Design, fabrication and optical characterization of photonic crystal assisted thin film monocrystalline-silicon solar cells

Abstract

In this paper, we present the integration of an absorbing photonic crystal within a monocrystalline silicon thin film photovoltaic stack fabricated without epitaxy. Finite difference time domain optical simulations are performed in order to design one- and two-dimensional photonic crystals to assist crystalline silicon solar cells. The simulations show that the 1D and 2D patterned solar cell stacks would have an increased integrated absorption in the crystalline silicon layer would increase of respectively 38% and 50%, when compared to a similar but unpatterned stack, in the whole wavelength range between 300 nm and 1100 nm. In order to fabricate such patterned stacks, we developed an effective set of processes based on laser holographic lithography, reactive ion etching and inductively coupled plasma etching. Optical measurements performed on the patterned stacks highlight the significant absorption increase achieved in the whole wavelength range of interest, as expected by simulation. Moreover, we show that with this design, the angle of incidence has almost no influence on the absorption for angles as high as around 60°.

Influence of patterning the TCO layer on the series resistance of thin film HIT solar cells

“…60-80 nm) [1,4,5,11,12]. Figure 4 shows the impact of the filling factor f f on the degradation ratio r. These simulations showed that it was not influenced by the orientation of the PC since we had exactly the same results (Fig.…”

“…The objective is to mimic nanopatterns like inverted nanopyramids (fabricated by wet etching [1,5,11]) and cylindrical nanoholes (obtained by dry etching [4,5,11,12]), covered by a partial TCO layer. Figure 3 represents the electric periodic elements for a PC made of a square lattice of squares, rounds and diamonds with a top finger aligned (a) or not (b) with the PC directions.…”

“…Theoretically, their energy conversion efficiencies may reach those of standard cells as long as the thickness of c-Si is at least of the order of 10 μm to 20 μm [1]. An efficient light trapping structure like a photonic crystal is necessary to enhance the absorption in the active material [1][2][3][4][5][6][7][8]. As surface recombinations are much more critical for thin solar cells, the HIT (Heterojunction with Intrinsic Thin layer) structure is a powerful solution since it currently allows the best conversion efficiency with a c-Si absorber [9].…”

Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

“…For the case of mono-crystalline silicon, periodic photonic nanostructures have been barely investigated optically but they have not been integrated in a solar cell so far [17][18][19][20][21][22].…”

Sunlight-thin nanophotonic monocrystalline silicon solar cells

“…Here, the nanocups pattern is selfassembled by hole-mask colloidal lithography, where the electrostatic forces result in a short-range order, featuring a near-neighbor distance Gaussian distribution [19]. With a peak at ∼580 nm and nanocups diameter of ∼600 nm, it presents for this film thickness the best compromise between light in-coupling, associated with small near-neighbor distances, and light-trapping of low-energy photons, requiring larger pitches [27][28][29]. Further, the nanocup depth-profile is a rounded square-based pyramid with the aspect ratio (length by diameter) of 0.9-1 and, importantly, without negative slopes (atomic-force microscopy (AFM) scans can be found in the supporting materials, figure S2).…”