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(a) Simple equivalent circuit for small signal measurements. Any lead inductance is neglected here. The series approximation is highlighted by a solid blue box and the parallel by a dashed red box. (b) Capacitance (1/C2) versus frequency characteristics of a PCBM only device. Both Cs and Cp parameters are shown. The calculated geometric capacitance (1/Cg 2) is highlighted by a gray line.
(a) Capacitance versus frequency characteristics of a typical P3HT:PCBM (1:1) BHJ PV device. The ellipse highlights the differences in the geometric capacitance obtained by each model. (b) Impedance versus frequency plots showing an exponential decrease in the impedance magnitude. The inset magnifies the 10 kHz–1.5 MHz regime where |Z| drops below 1 kΩ.
(a) Capacitance versus voltage characteristics for P3HT only device at 100 kHz and 1 MHz. The calculated geometric capacitance (Cg) is highlighted by the horizontal line. The differences in the geometric capacitance obtained by the models are shown within the circle. (b) Density of trap states versus demarcation energy for P3HT:PCBM (1:1) device. The arrow shows the shift in the Gaussian amplitude and central energy between the two models.
Capacitance versus frequency as a function of reverse bias for (a) the series model and (b) the parallel model. The arrows indicate the direction of increasing reverse bias.
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