Experimental Common Tools: (1) I-V Characterization & Measurement of Efficiency

Editor : Sapien

Bring it out for everyone
When you smile we can see the sun
Bring it out for all to hear
Because you’ve so much to give
And there’s so much to know
But if you wait for your moment
Well, it may never show.

– From “Know Who You Are”, sung by Supertramp”, sung by Queen

 The I-V characterization, a relationship between electrical current and voltage, is a basic and common method for nonlinear device characterization.

 If a system is linear then electrical current is proportional to applied voltage, and the inverse of linear coefficient we call as electrical resistance. From measured electrical resistance, and with known sample dimension, resistivity or conductivity can be calculated, which are characteristic parameters of the device or material

 If the system is nonlinear, electrical resistance or characteristic parameters are nonlinearly dependent upon voltage, current, temperature, time, or some other operating conditions. The I-V characterization is normally configured as voltage dependence of current or current dependence of voltage. Then such I-V characteristics, specifically I-V curves and characteristic parameters calculated from the curves, can be extended to the measurement of temperature dependence, time dependence (aging), and so on. The I-V curve is usually obtained by measurement of current during voltage sweep or scan.

 The resistance in nonlinear device is obtained from differential slope of the I-V curve. Since it is conventional to plot it as voltage in x-axis and current in y-axis, it becomes the inverse of the slope. Device properties like electrical resistance can be represented as a function of voltage (or current) and can be used as numerical simulation and digital application of device operation.

 Among many characteristic parameters derived from I-V curve, calculations of electrical power and energy are essential. The I-V characterization is a common method for quantification of electrical input or output power and energy, in terms of efficiency of the device.

 Diode is a typical example of nonlinear electrical device. Its I-V curve shows exponential increase of current at forward bias and ideally zero but possibly some leak current at reverse bias.

 LED (Light Emitting Diode) is an energy conversion device from electricity to light, and its input characteristics are of diode type. Measured light output power can be characterized as a function of input voltage, and with current measurement the LED light conversion efficiency (Lm/W) can be calculated.

 Photovoltaic cell is another energy conversion device of diode type, but on the contrary, from light to electricity. From known input light (solar) power and measurement of output I-V curve, solar conversion efficiency and fill facator are obtained as characteristic device parameters.

 FET (Field Effect Transistor) and TFT (Thin Film Transistor) are a sort of two-diode device having two control voltages. Various characteristic device parameters such as threshold voltage, on-off ratio, subthreshold slope and carrier mobility can be obtained from their I-V curve measurement.

 Battery is an electrochemical device and the current and voltage between two electrodes of the battery are nonlinear. The internal resistance of the battery is related to the differential coefficient of I-V characteristics. The Coulomb efficiency of the battery is a ratio of the total output energy during discharge with respect to the total input energy during charge in a charge-discharge cycle.

 In terms of electrochemistry, voltammetry can be categorized as I-V characterization experiment. In particular, the cyclic voltammetry is a useful method to obtain nonlinear I-V curve for electrochemical cell, and repeated cycling shows time dependence of I-V characteristics and useful for degradation analysis of electrochemical cell.

 McScience provides various test systems, instruments and softwares for I-V characterization and efficiency measurement of various test devices and materials such as LED, OLED, TFT, solar cell, battery, electrochemical cell, organic semiconductor, and so forth.