Determination of Charge-Carrier Mobility and Built-In Potential in Thin-Film Organic M-I-M Diodes from Extraction-Current Transients

Staffan Dahlström, Oskar J. Sandberg, Mathias Nyman, and Ronald Österbacka

Phys. Rev. Applied 10, 054019 – Published 8 November 2018

Abstract

We have extended the Charge Extraction by a Linearly Increasing Voltage (CELIV) technique for determination of the built-in potential and the charge-carrier mobility in thin-film metal-insulator-metal (M-I-M) diodes. The validity of the presented analytical theory is verified by drift-diffusion simulations and experimentally demonstrated on organic solar cells. In contrast to the original CELIV theory, which assumes a uniform charge-carrier distribution in the active layer of the device, here we derive an analytical expression for determining the built-in potential and mobility in the case of a nonuniform charge-carrier distribution where charges have diffused into the active layer from the contacts. The extended CELIV theory is applicable on all thin-film M-I-M diodes, e.g., organic solar cells. Drift-diffusion simulations show that the error for mobility estimation can be an order of magnitude if not correcting for the carrier profile.