Extraction of photogenerated charge carriers by linearly increasing voltage in the case of Langevin recombination

Abstract

Charge extraction by linearly increasing voltage (CELIV) is a powerful and widely used technique for studying charge transport physics, particularly in disordered systems such as organic semiconductors. In this article, we show that CELIV photocurrent transients are strongly dependent on experimental conditions, such as the light intensity and absorption profile. With this in mind, we introduce a universal correction factor that qualitatively extends previously derived CELIV equations, allowing carrier mobility to be estimated at various photogenerated carrier concentrations and, most importantly, photogeneration profiles. In addition, we demonstrate how the CELIV technique can be conveniently used to determine precisely the presence of Langevin bimolecular carrier recombination.

Investigation of charge carriers transport from extraction current transients of injected charge carriers

“…Recently, charge carriers extraction by the linearly increasing voltage method (CELIV) became widely used for the investigation of the photogenerated charge carriers transport properties in the thin organic films and highly conductive materials also [1][2][3]. However, due to Langevin recombination, which is typical for low mobility materials, and the influence of the initial distribution of the photogenerated charge carriers, the large errors (more than one order of magnitude) in the estimation of the mobility may occur [4].…”

Molecular weight dependent bimolecular recombination in organic solar cells

“…[21][22][23][24][25][26] The recombination coefficient can be estimated from the maximum extraction current in the photo-CELIV transient. 27,28 However, this transient is influenced by experimental factors that are not fully accounted for in the theory, such as the spatial distribution of light absorption, 28 the circuit resistance, 29 and the voltage slope. 30 Additionally, premature escape of carriers from the film 31 contributes to the charge redistribution during the delay time, 32 which results in a false position of the extraction maximum and makes the measurement unreliable.…”

Charge carrier transport and recombination in disordered materials

“…This method can only be used to measure the mobility of majority charge carriers, and also, using photo-CELIV errors may occur due to the influence of the initial distribution and recombination of the photogenerated charge carriers [12,13]. In Ref.…”