Keithley 2876 Photovoltaic App Note free download

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Number 2876 Application Note Making IV and CV Measurements on Solar/ Series Photovoltaic Cells Using the Model 4200SCS Semiconductor Characterization System Introduction parameter because it reduces both the short-circuit current and the maximum power output of the cell. Ideally, the series resis- Because of the increasing demand for energy and the limited tance should be 0 (rs = 0). The shunt resistance represents the supply of fossil fuels, the search for alternative sources of power loss due to surface leakage along the edge of the cell or due to is imperative. Given that there is a vast amount of energy avail- crystal defects. Ideally, the shunt resistance should be infinite (rsh able from the sun, devices that convert light energy into elec- = ). trical energy are becoming increasingly important. Solar or photovoltaic (PV) cells convert light energy into useful electrical PV Cell rs power. These cells are produced from light-absorbing materials. When the cell is illuminated, optically generated carriers produce Photon h an electric current when the cell is connected to a load. IL rsh Load RL A variety of measurements are made to determine the elec- trical characteristics of PV cells. Characterizing the cells often involves measuring the current and capacitance as a func- tion of an applied DC voltage. The measurements are usually Figure 1. Idealized equivalent circuit of a photovoltaic cell done at different light intensities and temperature conditions. Important device parameters can be extracted from the current- If a load resistor (R L) is connected to an illuminated PV cell, voltage (I-V) and capacitance-voltage (C-V) measurements, such then the total current becomes: as the conversion efficiency and the maximum power output. Electrical characterization is also important to determine losses I = IS(eqV/kT