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Light and Dark Current-Voltage Fits of Bulk Heterojunction Cells Using a New Analytical Drift-Diffusion Model
K. Taretto, A. Koffman-Frischknecht, M. Soldera
Subtopic: Organic-based PV
Event: 28th European Photovoltaic Solar Energy Conference and Exhibition
Session: 3DV.2.8
2718 - 2722
ISBN: 3-936338-33-7
Paper DOI: 10.4229/28thEUPVSEC2013-3DV.2.8
0,00 EUR
Document(s): paper, poster


Fitting experimental current(J)-voltage(V) characteristics by analytical models helps to draw a relatively simple physical image of a given solar cell. Here, we adapt a new model for p-i-n solar cells, which includes interface potential drops and surface recombination, to bulk heterojunction (BHJ) cells. This yields a closed form JV curve having a voltage-dependent ideality factor that emerges as a natural consequence of the spatial distribution of charge carriers. The JV equation is tested by fitting experimental data of state of the art BHJ cells prepared with three different donor-acceptor blends. We show that it is sufficient to use an infinite surface recombination velocity and four fit parameters, namely series and shunt resistance, lifetime and mobility, to obtain fits with overall errors below 2 %. From both light and dark JV curves, we obtain free carrier lifetimes between 0.4 μs and 12 μs, and mobilities between 10-4 cm2/Vs and 10-3 cm2/Vs. In contrast to single diode electrical models, the proposed drift-diffusion model is able to explain current-voltage curves of BHJ cells avoiding the use of effective ideality factors or saturation currents, and to show the voltage-dependent nature of the photocurrent.