Exact analytical solution of a two diode circuit model for organic solar cells showing S-shape using Lambert W-functions

► We have obtained exact analytical expression for I–V curves for OSC showing S-shape. ► The model includes an extra diode (in reverse bias) and an extra parallel resistance. ► Simulations varying these extra parameters have been performed. ► Circuit parameters have been extracted by fitting the mod...

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Bibliographic Details
Published in:Solar energy 2012-10, Vol.86 (10), p.3026-3029
Main Authors: Romero, B., del Pozo, G., Arredondo, B.
Format: Article
Language:English
Subjects:
Applied sciences
Approximation
Circuits
Diodes
Direct energy conversion and energy accumulation
Disturbances. Regulation. Protection
Electrical engineering. Electrical power engineering
Electrical power engineering
Energy
Equivalent circuit
Exact sciences and technology
Mathematical functions
Mathematical models
Natural energy
Organic solar cells
Photoelectric conversion
Photovoltaic cells
Photovoltaic conversion
Power networks and lines
S-shape
Solar cells. Photoelectrochemical cells
Solar energy
W-Lambert
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Summary:► We have obtained exact analytical expression for I–V curves for OSC showing S-shape. ► The model includes an extra diode (in reverse bias) and an extra parallel resistance. ► Simulations varying these extra parameters have been performed. ► Circuit parameters have been extracted by fitting the model to experimental data. Organic solar cells (OSCs) often show a kink, also called S-shape, in the current–voltage (I–V) characteristics, that has been attributed to different physical phenomena such as poor quality of cathode-active layer interface or unbalance charge carrier mobilities. This non-ideal behaviour can be electrically modelled including a second diode, in reverse bias, together with an extra shunt resistance (RP2) in the traditional solar cell equivalent circuit. In this paper, we solve without approximations the transcendental equation system derived from this modified circuit. We have obtained an analytical expression for I–V curves decoupling the voltage drop in each diode using Lambert W function. This expression has been fitted to experimental data in order to obtain circuital parameters. Simulations varying saturation current of reverse diode (I02) and RP2 have been performed in order to study the dependence of S-shape with these parameters.
ISSN:0038-092X
1471-1257
DOI:10.1016/j.solener.2012.07.010