Silicon solar cells: toward the efficiency limits

Figures & data

Figure 1. Schematic geometry of (a) a solar cell with a single layer leading to single-pass absorption or (b) a layer with a Lambertian scatterer in the front and a back reflector in the rear side, leading to Lambertian light trapping; (c) short-circuit current density $J_{sc}$ for c-Si, a-Si:H, GaAs, and CIGS (taking $x=0.08$) as a function of thickness, under AM1.5 solar spectrum. Dashed lines refer to the single-pass case, while solid lines refer to the Lambertian limit with $R_b=1$, as defined in Ref. [18]. Reflection losses are neglected throughout. Notice that the silicon curves differ from those published in Ref. [23], due to the use of different data for c-Si [19,24] and for a-Si:H [20].

Figure 2. (a) Photogeneration profile of a 10-µm thick c-Si solar cell with Gaussian disorder, described by the RMS deviation of height $\sigma =300$ nm and the lateral correlation length l_c = 160 nm. The whole cell is shown in the inset, while the main plot shows the photogeneration profile close to the texture. All lengths are in µm. Reprinted from Ref. [87], with the permission of AIP Publishing. (b) Structure considered in the FEM simulations. The p-n junction is made of an 80-nm thick n-type layer with donor concentration N_d = 10¹⁹ cm⁻³, and a p-type layer of thickness d−80 nm with acceptor concentration N_a = 10¹⁶ cm⁻³. The ARC and silver layers serve as front and back contacts, respectively.

Figure 3. The main electrical parameters for c-Si solar cells without surface recombination: (a) open-circuit voltage $V_{\mathrm{o}\mathrm{c}}$ and short-circuit current density $J_{\mathrm{s}\mathrm{c}}$, (b) fill factor FF and conversion efficiency η. The diffusion lengths related to SRH recombination are L_B = 232 µm for electrons in the p-type base [90], and L_E = 23.2 µm for holes in the n-type emitter [25].

Figure 4. (a) Energy conversion efficiency for solar cells with perfect surface passivation (S_B = S_E = 0 cm/s) as a function of the electron diffusion length in the base $L_{\mathrm{B}}$ (with L_E = 23.2 µm) and of the cell thickness. The optimal configurations lie along the blue solid line with symbols. (b) Energy conversion efficiency as a function of the back surface recombination velocity $S_{\mathrm{B}}$ and of the cell thickness for L_B = 232 µm, L_E = 23.2 µm, and S_E = 10³ cm/s. All results are calculated by the FEM. Reprinted (with adaptation) from Ref. [88], with permission from Elsevier.

Figure 5. (a) Scheme of the p-n junction for the generalized Hovel model. The impurity charges in the space charge region correspond to an n-emitter, p-base configuration, although the formulation of the model applies to both n-p and p-n configurations. The emitter is usually more narrow and highly doped than the base. (b) Scheme of the solar cell structure for the three models, including front and back contacts (serving also as ARC and back reflector, respectively) and the Lambertian scattering layer.

Figure 6. (a) Short-circuit current density $J_{\mathrm{s}\mathrm{c}}$, (b) open-circuit voltage $V_{\mathrm{o}\mathrm{c}}$, (c) fill factor FF, and (d) efficiency $\eta$ as a function of the absorber thickness. Results are calculated with the diode equation model (red lines), with the generalized Hovel model (blue dotted lines), and by the FEM method (black solid lines). We include only intrinsic Auger recombination, and assume no Shockley–Read–Hall or surface recombination. The triangles indicate the parameters of the record silicon solar cell with 26.3% efficiency [6]. Reproduced (with adaptation) from Ref. [98], with permission from IOP Publishing.

Figure 7. Effect of Shockley–Read–Hall recombination, expressed by the diffusion length, $L_{\mathrm{B}}$, for different absorber thicknesses. Other parameters are the same as in Figure 6. Results are calculated with the generalized Hovel model.

Figure 8. Effect of surface recombination, expressed by the surface recombination velocity $S$ at the rear surface, for different absorber thicknesses. Other parameters are the same as in Figure 6. Results are calculated with the finite-element method.

Figure 9. (a) Scheme of the silicon/perovskite tandem solar cell. (b) Efficiency of the tandem as a function of the thickness of the silicon bottom cell, calculated for different values of the perovskite bandgap. Adapted from Ref. [98], with permission from IOP Publishing. Inset: maximum efficiency as a function of perovskite gap.

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