Quantum Yield and Surface Recombination

The photocurrent quantum efficiency, Y, of n-Si electrode in fluoride solutions depends on current as shown in Fig. 5.12. It is high at low current densities and decreases with increasing current densities to a plateau value of about 2 Fig. 5.12 shows 

FIGURE 5.11. Photocurrems at +0.2 V as a function of the pH in 1M NH4F solution. (Reprinted with permission from Gerischer and Lubke. 1987 Wiley-VCH.) 

FIGURE 5.12. The ratio n of collected charge carriers per incident photon as a function of the current density for 2.5% HF in aqueous solution. After Lehmann and Foil. (Reproduced by permission of The Electrochemical Society, Inc.) 

FIGURE 5.13. Intensity dependence of the quantum efficiency Q for n-Si (111) and the corresponding hydrogen production efficiency Tin measured in the ring-disk arrangement. Electrolyte 1.0moldm NH4F, pH 4.7. A, 632.8 nm. Rotation rate 20 Hz. (Reprinted from Blackwood et al. 1992, with permission from Elsevier Science.) 

FIGURE 5.14. Quantum efficiency of the photocurrent for an illuminated n-Si electrode measured in various solutions at l.OV versus SCE and 22°C (O) IM NH4F (pH 4.9) ( ) IM NH4F (pH 9.6) (A) phthalate buffer (pH 4.50). (Reprinted from Matsumura and Morrison, 1992, with permission from Elsevier Science.) 

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