Investigation of the Photocurrent in Bulk Heterojunction Solar Cells

Abstract

We investigated the photocurrent in poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C${}_{61}$ butyric acid methyl ester (PCBM) solar cells by applying a pulsed measurement technique. For annealed samples, a point of optimal symmetry (POS) with a corresponding voltage $V_{\text{POS}}$ of 0.52--0.64 V could be determined. Based on macroscopic simulations and results from capacitance--voltage measurements, we identify this voltage with flat band conditions in the bulk of the cell, but not the built-in voltage as proposed by [Ooi et al., J. Mater. Chem. 18 (2008) 1644]. We calculated the field dependent polaron pair dissociation after Onsager--Braun and the voltage dependent extraction of charge carriers after Sokel and Hughes with respect to this point of symmetry. Our analysis allows to explain the experimental photocurrent in both forward and reverse directions. Also, we observed a voltage--independent offset of the photocurrent. As this offset is crucial for the device performance, we investigated its dependence on cathode material and thermal treatment. From our considerations we gain new insight into the photocurrent`s voltage dependence and the limitations of device efficiency.

6 pages, 7 figures

References in corpus (4)

• Origin of the Efficient Polaron Pair Dissociation in Polymer--Fullerene Blends
• Origin of Reduced Polaron Recombination in Organic Semiconductor Devices
• Polaron Recombination in Pristine and Annealed Bulk Heterojunction Solar Cells
• Bipolar Charge Transport in Poly(3-hexyl thiophene)/Methanofullerene Blends: A Ratio Dependent Study

Cited by in corpus (7)

• Polymer-Fullerene Bulk Heterojunction Solar Cells
• Charge density dependent nongeminate recombination in organic bulk heterojunction solar cells
• Shockley Equation Parameters of Organic Solar Cells derived by Transient Techniques
• Relation of open circuit voltage to charge carrier density in organic bulk heterojunction solar cells
• Built-in potential and validity of Mott--Schottky analysis in organic bulk heterojunction solar cells
• Direct and charge transfer mediated photogeneration in polymer-fullerene bulk heterojunction solar cells
• Comment on "Interface state recombination in organic solar cells"