Shockley Equation Parameters of Organic Solar Cells derived by Transient Techniques

Abstract

The Shockley equation (SE), originally derived to describe a p--n junction, was frequently used in the past to simulate current--voltage (j/V) characteristics of organic solar cells (OSC). In order to gain a more detailed understanding of recombination losses, we determined the SE parameters, i.e. the ideality factor and the dark saturation current, from temperature dependent static j/V-measurements on poly(3-hexylthiophene-2,5-diyl)(P3HT):[6,6]-phenyl-C${}_{61}$ butyric acid methyl ester (PCBM) bulk heterojunction solar cells. As we show here, these parameters are directly related to charge carrier recombination and become also accessible by transient photovoltage and photocurrent methods in the case of field-independent charge carrier generation. Although determined in very different ways, both SE parameters were found to be identical. The good agreement of static and transient approaches over a wide temperature range demonstrates the validity of the Shockley model for OSC based on material systems satisfying the requirement of field-independent polaron-pair dissociation. In particular, we were able to reproduce the photocurrent at various light intensities and temperatures from the respective nongeminate recombination rates. Furthermore, the temperature dependence of the dark saturation current $j_0$ allowed determining the effective band gap of the photoactive blend perfectly agreeing with the literature values of the energy onset of the photocurrent due to charge transfer absorption. We also present a consistent model directly relating the ideality factor to recombination of free with trapped charge carriers in an exponential density of tail states. We verify this finding by data from thermally stimulated current measurements.

8 pages, 6 figures

References in corpus (9)

• Polymer-Fullerene Bulk Heterojunction Solar Cells
• Origin of the Efficient Polaron Pair Dissociation in Polymer--Fullerene Blends
• Oxygen doping of P3HT:PCBM blends: Influence on trap states, charge carrier mobility and solar cell performance
• Charge density dependent nongeminate recombination in organic bulk heterojunction solar cells
• Charge Carrier Concentration and Temperature Dependent Recombination in Polymer Fullerene Solar Cells
• Relation of open circuit voltage to charge carrier density in organic bulk heterojunction solar cells
• Influence of Phase Segregation on Recombination Dynamics in Organic Bulk-Heterojunction Solar Cells
• Investigation of the Photocurrent in Bulk Heterojunction Solar Cells
• Direct and charge transfer mediated photogeneration in polymer-fullerene bulk heterojunction solar cells

Cited by in corpus (10)

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• How to Reduce Charge Recombination in Organic Solar Cells: There Are Still Lessons to Learn from P3HT:PCBM
• Visualising the Vertical Energetic Landscape in Organic Photovoltaics
• Molecular weight dependent bimolecular recombination in organic solar cells
• Order of Decay of Mobile Charge Carriers in P3HT:PCBM Solar Cells
• Power-law density of states in organic solar cells revealed by the open-circuit voltage dependence of the ideality factor
• Transport resistance strikes back: unveiling its impact on fill factor losses in organic solar cells
• Electric field induced negative capacitance in semiconducting polymer
• Diffusion of a particle in the spatially correlated exponential random energy landscape: transition from normal to anomalous diffusion