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Transient charge extraction (CE) experiments in organic photovoltaics can overestimate recombination rates due to unaddressed recombination during extraction. This study introduces a corrected analytical model for accurate bimolecular recombination rate constants in low-mobility devices.

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Area of Science:

  • Organic electronics
  • Photovoltaics
  • Charge transport phenomena

Background:

  • Recombination of free charges is a primary performance limitation in organic semiconductor devices.
  • Transient charge extraction (CE) experiments are commonly used to determine recombination kinetics.
  • Existing CE methods often overlook recombination during the extraction process, particularly in low-mobility materials.

Purpose of the Study:

  • To investigate the validity of transient charge extraction (CE) experiments in low-mobility organic semiconductor devices.
  • To quantify the impact of recombination during extraction on measured recombination rate constants.
  • To develop and validate a new analytical model for accurate determination of recombination kinetics.

Main Methods:

  • Transient drift-diffusion simulations were employed to model charge carrier behavior.
  • Numerical simulations were used to validate the proposed analytical model.
  • The analytical model was applied to correct experimental data for bimolecular recombination rate constants.

Main Results:

  • Recombination during transient extraction leads to incomplete charge extraction (CE).
  • This incomplete CE results in apparent carrier density-dependent recombination rate constants and overestimated recombination orders.
  • The observed effects are dependent on charge carrier mobilities and the device's resistance-capacitance time constant.

Conclusions:

  • The standard transient charge extraction (CE) experiment is not fully valid for low-mobility organic devices due to recombination effects.
  • An analytical model accounting for recombination during extraction provides accurate bimolecular recombination rate constants.
  • This work offers a method to correct experimental data and improve the understanding of recombination in organic photovoltaics.