Polycrystalline cells consist of grains with different sizes. Figure 2.31 on p. 49 shows the measured log-normal grain size distribution that is well described by the function [200,201] ( Ґ — 2^ 1 1 [ ln(G/ G) cr’ (^exphl—-% which that describes a Gaussian distribution of the logarithm of the grain size G. The average […]

The local carrier collection probability rfc(Z) is defined as the probability that a carrier generated at the depth Z is collected at the junction of a short-circuited cell. In this sec­tion, we assume a planar cell of thickness ^ with one-dimensional transport and the cell surface located at Z = 0. In contrast to the […]

Minority carrier recombination in polycrystalline semiconductor materials occurs in the volume of the grains, at the grain boundaries and at the surface of the cell. The quantum efficiency model has therefore to account for all three locations of recombina­tion. Three-dimensional modeling is necessary. Referring to the cell geometry shown in Figure 2.28 on p. 46, […]

Quantum efficiency diffusion length Lq For planar monocrystalline sheets of Si material, the effective quantum efficiency diffusion length depends on the diffusion length L of the semiconductor, the back surface recombination velocity Sb, the base thickness Wbas, and the minority carrier diffusion coefficient Dn [24]. The value of LQmono equals the effective current-voltage diffusion length […]

As sketched in Figure 3.2 on p. 56, a quantum efficiency spectrum of a crystalline thin-film cell shows, in general, two linear regions if plotted as IQE~La ). Both regions define an effective diffusion length: • The length Lq that we call the quantum efficiency diffusion length and that we derive from the IQE spectrum […]

Illuminating the cell through the back achieves a higher sensitivity to the back surface recombination than illumination through the front surface. Obviously, the cell has to be bifacially sensitive to permit rear illumination. The quantum efficiency for back illumi­nation is [409, 410] IQE =———————- A——————– (C.9) cosh(^/I) + -^-sinh(^os/I) Here, plotting IQE versus La yields […]

C. 2.1 Front illumination The standard technique for the evaluation of internal quantum efficiency spectra [36] assumes a cell that is thick, compared to the optical absorption length La = l/as, and has a spatially homogeneous minority carrier diffusion length. Here, as denotes the absorp­tion coefficient of crystalline Si. The profile of the minority carrier […]

Figure C.3 shows the quantum efficiency of a high-efficiency thin-film Si solar cell with a thickness of 46.5 pm (see description of Cell A on p. 83 for more details) under illumination with light of wavelengths 500 and 800 nm. For both wavelengths the IQE data depend on the forward bias voltage Ub. At bias […]