Current-light-voltage curves

Fig. n. 17 Current—light—voltage curves of PLEDs with 4% btp2lr(acac)-doped PVK PBO matrix as the emitting medium. The inset shows electroluminescence from the same device [80]. 

The photocurrent density (/ph) is proportional to the light intensity, but almost independent of the electrode potential, provided that the band bending is sufficiently large to prevent recombination. At potentials close to the flatband potential, the photocurrent density again drops to zero. A typical current density-voltage characteristics of an n-semiconductor electrode in the dark and upon illumination is shown in Fig. 5.61. If the electrode reactions are slow, and/or if the e /h+ recombination via impurities or surface states takes place, more complicated curves for /light result. 

In Fig. 16 we show a current-voltage curve for >-type GaP in the presence of a dye in the dark and at illumination with light being only absorbed by the dye. We see again a saturation current, now however, in cathodic direction. The photocurrent spectrum is represented in Fig. 17. It corresponds fully with the absorption spectrum of the adsorbed dye. One sees a saturation current at a polarisation of more than 0.35 eV negative of the flat band potential. Some special features at GaP-electrodes seem to be caused by the existence of surface states with energies in the range of the band gap. It has been assumed that these surface states can... 

Figure 7. Current-voltage curves in the dark and under illumination (680-nm light, 1 mV [cm2) of a MoS2 electrode of -c orientation at different states of surface perfection (15) (1) freshly cleaved (2) after 25-min photocorrosion (solar light of AM 1) at 1 VSCE in 1M KCl solution (3) after 115-min photocorrosion, same conditions as (2) electrolyte 1M KCl + 0.05M Kl...

Figure 5. Current—voltage curves of a TiOs electrode in 1.0M KOH with 200 mV/s scan from 0 V (SCE). Curve 1, in dark Curve 2, with 350-run light on Curve 3, in dark after 30 s illumination with 350-nm light atO V (SCE) (28).

Figure 7. Current-voltage curves for a Ru(4-OH,3-COOH,o-phen)(bipy)t(PFe) coated TiOt electrode in pH 7 NatSOt. Current curves analogous to Curves 1 and 3 in Figure 5 except the illumination was at +0.5 V and with 470 nm light.

Fig. 1 Detail of the photocurrent-voltage curve under hand chopped light showing the cathodic current superimposed to the anodic photocurrent.

Fig. 1.33. Semi-logarithmic plot of the current/voltage curves of a PET/ITO/PEDOT-PSS/OPV4 C60/A1 photovoltaic cell in which OPV4-C60 is the active material. Open squares represent dark curve and solid squares were recorded under about 65 mW cm-2 white light illumination...

Fig. 98. (A) Current-voltage curves for n-GaAs/selenide junction under (a) 1.5 mW cm 2, (b) 9mWera"2, (c) 22raWcm"2, and (d) 50mWcm"2. (B) Mott-Schottky plots using data from the equivalent circuit of Fig. 97(a) at light intensities as in (A). The line (e) was obtained in the dark and gives Vn, - 2.06 V/SCE.

Referring back to Figure 13, the current-potential curves under illumination of the semiconductor simply appear shifted up relative to the dark i- V counterpart. This, however, is the ideal scenario. Anomalous photoeffects (APEs) are often observed that manifest as a cross-over of light and dark current-voltage curves, as illustrated in Figure 22. Thus, the superposition principle [241] is not obeyed in this instance. The dashed line in Figure 22 is produced by translating the photoeurrent-... 

Figure 22. Anomalous photoeifect (APE) showing cross-over of the dark and light current-voltage curves for an n-type semiconductor-based interface. The dashed line is obtained as described in the text.

Figure 11 Performance of an A11 chlorophyll a Hg photovoltaic cell (A1 negative). Cell area 0.25 cm2, (above) Photocurrent-voltage curve for incident light power 6 x 10-8 W at 745 nm. (below) Light intensity dependence of open-circuit voltage and short-circuit current...

Fig. 8. Current-voltage curves for p-InP cathode in the light (1) and Pt cathode in the dark (2) in 1 M HCIO4 solution under 79 mW/cm solar illumination. Hatched area is proportional to the converted energy [38],...

The photocurrent increases linearly with incident light intensity, as shown in the current versus voltage (/-V) characteristic curve for a photodiode (see Figure 13.6b) however, note that saturation (i.e. no further increase in current) in photodiodes is typically reached for light exposure of 1—2 mW. 

A further difference between metal and semiconductor electrodes is that electron transfer at semiconductors can involve minority carriers generated by light, and while in the dark only small currents flow when a depletion layer is formed at the semiconductor solution interface, illumination of the electrode gives rise to much larger photocurrents. The current-voltage curves for semiconductor electrodes are therefore not only dependent on whether the semiconductor is n- or p-type but also on whether the electrode is in the dark or illuminated with light of sufficient energy to promote electrons from the valence band to the conduction band. Instead of the symmetrical Butler-Volmer plots obtained for metal electrodes, essentially diode-like behaviour is expected for extrinsic semiconductor electrodes, as shown in Fig. 3.18. 

Fig. 2 Illustrative photocurrent-voltage curves for a solar cell (SC) (1) in the dark and (2) under light illumination. Voa open-circuit voltage, Vinp and ,p voltage and photocurrent corresponding to maximum power of the SC, respectively, jsc short-circuit current, 7 maximum power of the SC, ml ideai niaximum power of an ideal SC, i.e., which converts all photogenerated charge to energy and passes it into an external circuit...

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