Current-voltage curves photovoltaics

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. 11.2 Current-voltage curves in the dark and under illumination for an electrochemical photovoltaic cell (with n-semiconductor)...

The point on the current—voltage curve for a photovoltaic cell at which the cell generates maximum power. 

Figure 4 Dark current-voltage curve of Sn02/PcGe(0H)2, PVA/ln photovoltaic cell.

Figure 18.2 presents a typical current-voltage curve and photovoltaic characteristics that define the performance of solar cell devices. The PCE of the cell depends mainly on the short-circuit current, /sc, the open-circuit voltage, Voc, and the fill factor, FF, as shown in Figure 18.2. 

M. R. Lilliedal, A. J. Medford, M. V. Madsen, K. Norrman and F. C. Krebs, The effect of post-processing treatments on inflection points in current-voltage curves of roll-to-roll processed polymer photovoltaics, SoL Energy Mater. Sol. Cells, 2010, 94, 2018-2031. 

A photovoltaic detector is often modeled as a current source which produces one hole-electron pair per absorbed photon. The circuit includes the detector s self-capacitance (including the depletion capacitance of the junction within the detector), and a parallel resistance (the inverse of the slope of the current-voltage curve of the detector at the bias point). The resistance and capacitance components... 

The photocurrent-voltage curve of a cell made with the I /I2 redox couple (Fig. 8) shows behavior typical of the standard DSSC. The substantial photovoltaic effect is expected from the fact that the dark current (Fig. 4) is negligible positive of about -0.5 V. On the other hand, a cell made with the FcCp2 70 redox couple shows no measurable photoeffect Its current under illumination (Fig. 8) is essentially equal to its dark current (Fig. 4). The photovoltaic effect is negligible because practically all photogenerated charge carriers recombine before they can be collected in the external circuit. In general, fast rates of reactions (4) and (5) tend to eliminate the photovoltaic effect in DSSCs. 

The operation of a photovoltaic system is governed by the current-voltage characteristic curves of the photovoltaic module. Such a set of curves, for different values of the incident solar irradiance and constant photovoltaic module temperature, is shown in Figure 2.4. The curves consist of two parts. In the first part the photovoltaic module behaves as a constant-current source, with amplitude proportional to the solar irradiance level. In the rest of the curve, current decays... 

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...

Evaluation of an SC photovoltaic performance is usually accomplished with a set of tests. Those involve measurements of the current-voltage (I-V) curves for the cell in the dark and under light illumination, fluorescent decay upon photoexcitation, determination of the incident photon-to-electron-conversion efficiency (TPCE), etc. 

The photovoltaic effect, which is utilized in the manufacture of solar cells, corresponds to quadrant IV of the current-voltage (I-V) curve drawn in... 

Fig. 5. Current-voltage (I-V) curves showing the photovoltaic effects of the devices before heating (solid square), after 80 °C heating for 1 minute (empty circle), and after 80 °C heating under 4V forward bias (sohd triangle).

In a bulk-heterojunction photovoltaic cell with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as an electron acceptor, alternating copolymer 19 (Fig. 9), derived from 2,7-fluorene and 2,5-dithienylsilole, can show impressive performance as the electron donor.31 In a device configuration of ITO/PEDOT/active layer/Ba/Al, the dark current density—bias curve shows a small leakage current, suggesting a continuous, pinhole-free active layer in the device. Under illumination of an AM 1.5 solar simulator at 100 mW/cm2, a high short-circuit current of 5.4 mA/cm2, an open-circuit voltage of 0.7 V, and a fill factor of 31.5% are achieved. The calculated energy conversion efficiency is 2.01%. 

Hegedus et al. [146] also measured the I-V curves of amorphous Si p-i-n solar cells at different temperatures. The curves in the dark and also under illumination are shown in Fig. 5.25. The I-V curves under illumination obey Eq. (5.8) in this case also. The built in voltage calculated from the illuminated curves was satisfactory. Hegedus et al. [146] took small portion of the dark I-V curves which could be represented by an equation of the type (5.5). They then attempted to derive the built in voltage using this dark current as Shockley currents. They obtained very strange results. Hegedus et al. [146] wrote Our results also clearly demonstrate that it is completely inappropriate to analyze J( V) data measured in the dark on a-Si p-i-n devices and then attempt to correlate the results with photovoltaic performance Measurements in the dark are not applicable to understand-... 

Thus, the J V curve under illumination is described as a superposition of the dark current and a crrrrent source that takes into accormt the photovoltaic effect in the device. The superposition means that this current source is independent of applied voltage and depends only on illumination. In addition, it is often implicitly... 

The interface between the renewable source and RFC system must match their current and voltage, which differ for solar and wind systems. Photovoltaic solar systems generate direct current, which may be used directly by the electrolyzer if their polarization curves are well matched, otherwise a DC/DC converter may be needed. Wind generators typically generate AC, so the interface must include an AC/DC inverter, similar to the electrolyzer s regulated voltage power supply. 

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