Effects of the charge-transfer reorganization energy on the open-circuit voltage in small-molecular bilayer organic photovoltaic devices

Comparison of the influence of deposition rates of the donor

Chih Chien Lee, Wei Cheng Su, Wen Chang Chang

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The theoretical maximum of open-circuit voltage (VOC) of organic photovoltaic (OPV) devices has yet to be determined, and its origin remains debated. Here, we demonstrate that VOC of small-molecule OPV devices can be improved by controlling the deposition rate of a donor without changing the interfacial energy gap at the donor/acceptor interface. The measurement of external quantum efficiency and electroluminescence spectra facilitates the observation of the existence of charge transfer (CT) states. A simplified approach by reusing the reciprocity relationship for obtaining the properties of the CT states is proposed without introducing complex techniques. We compare experimental and fitting results and propose that reorganization energy is the primary factor in determining VOC instead of either the CT energy or electronic coupling term in bilayer OPV devices. Atomic force microscopy images indicate a weak molecular aggregation when a higher deposition rate is used. The results of temperature-dependent measurements suggest the importance of molecular stacking for the CT properties.

Original languageEnglish
Pages (from-to)12651-12661
Number of pages11
JournalPhysical Chemistry Chemical Physics
Volume18
Issue number18
DOIs
Publication statusPublished - Jan 1 2016
Externally publishedYes

Fingerprint

Open circuit voltage
Deposition rates
open circuit voltage
Charge transfer
volatile organic compounds
Volatile organic compounds
charge transfer
interfacial energy
energy
Electroluminescence
Quantum efficiency
Interfacial energy
electroluminescence
quantum efficiency
Atomic force microscopy
Energy gap
Agglomeration
atomic force microscopy
Molecules
electronics

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

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abstract = "The theoretical maximum of open-circuit voltage (VOC) of organic photovoltaic (OPV) devices has yet to be determined, and its origin remains debated. Here, we demonstrate that VOC of small-molecule OPV devices can be improved by controlling the deposition rate of a donor without changing the interfacial energy gap at the donor/acceptor interface. The measurement of external quantum efficiency and electroluminescence spectra facilitates the observation of the existence of charge transfer (CT) states. A simplified approach by reusing the reciprocity relationship for obtaining the properties of the CT states is proposed without introducing complex techniques. We compare experimental and fitting results and propose that reorganization energy is the primary factor in determining VOC instead of either the CT energy or electronic coupling term in bilayer OPV devices. Atomic force microscopy images indicate a weak molecular aggregation when a higher deposition rate is used. The results of temperature-dependent measurements suggest the importance of molecular stacking for the CT properties.",
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