Nongeminate recombination in neat P3HT and P3HT:PCBM blend films

Abstract

The slow decay of charge carriers in polymer-fullerene blends measured in transient studies has raised a number of questions about the mechanisms of nongeminate recombination in these systems. In an attempt to understand this behavior, we have applied a combination of steady-state and transient photoinduced absorption measurements to compare nongeminate recombination behavior in films of neat poly(3-hexyl thiophene) (P3HT) and P3HT blended with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Transient measurements show that carrier recombination in the neat P3HT film exhibits second-order decay with a recombination rate coefficient that is similar to that predicted by Langevin theory. In addition, temperature dependent measurements indicate that neat films exhibit recombination behavior consistent with the Gaussian disorder model. In contrast, the P3HT:PCBM blend films are characterized by a strongly reduced recombination rate and an apparent recombination order greater than two. We then assess a number of previously proposed explanations for this behavior, including phase separation, carrier concentration dependent mobility, non-encounter limited recombination, and interfacial states. In the end, we propose a model in which pure domains with a Gaussian density of states are separated by a mixed phase with an exponential density of states. We find that such a model can explain both the reduced magnitude of the recombination rate and the high order recombination kinetics and, based on the current state of knowledge, is the most consistent with experimental observations.

9 pages, 4 figures; corrected a few minor typos and grammatical errors

References in corpus (9)

• Oxygen doping of P3HT:PCBM blends: Influence on trap states, charge carrier mobility and solar cell performance
• Origin of Reduced Polaron Recombination in Organic Semiconductor Devices
• Charge density dependent nongeminate recombination in organic bulk heterojunction solar cells
• Polaron Recombination in Pristine and Annealed Bulk Heterojunction Solar Cells
• Trap Distribution and the Impact of Oxygen-induced Traps on the Charge Transport in Poly(3-Hexylthiophene)
• Shockley Equation Parameters of Organic Solar Cells derived by Transient Techniques
• Charge Carrier Concentration and Temperature Dependent Recombination in Polymer Fullerene Solar Cells
• Direct and charge transfer mediated photogeneration in polymer-fullerene bulk heterojunction solar cells
• Comment on "Interface state recombination in organic solar cells"

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• Persistent photovoltage in methylammonium lead iodide perovskite solar cells
• How to Reduce Charge Recombination in Organic Solar Cells: There Are Still Lessons to Learn from P3HT:PCBM
• Power-law density of states in organic solar cells revealed by the open-circuit voltage dependence of the ideality factor
• Two-dimensional bimolecular recombination in amorphous organic semiconductors
• Rethinking Charge Transport and Recombination in Donor-diluted Organic Solar Cells