Performance and stability improvement in organic photovoltaics using non-toxic PEIE interfacial layers

Abstract

The improvement in current density–voltage characteristics and external quantum efficiency of organic photovoltaics with non-toxic polyethylenimine ethoxylated (PEIE) as a modified layer between the electron transport layer and the active layer were demonstrated. The mechanisms of carrier transport, photon generation current, and the carrier recombination influenced by the PEIE layer were systematically studied. An extra PEIE layer was demonstrated having a shorter relaxation time via pump-probe spectroscopy, which provides better charge transfer ability. From capacitance-voltage measurement, the effective capacitance of the device increase with an addition PEIE layer, corresponding to the increase of accumulation carriers generated at the interfaces. Furthermore, electrochemical impedance spectroscopy elucidated that the PEIE layer can reduce the carrier recombination probability in the devices. As a result, the lifetime of the devices with a PEIE layer is improved as compared to the devices without PEIE layer. • A non-toxic PEIE layer was demonstrated as having a shorter carrier relaxation time via pump-probe spectroscopy, which provides better charge transfer ability in OPV. •The non-toxic PEIE layer not only provides larger effective capacitance of the device resulting from amount of accumulation carriers generated at the interfaces, but also reduces the carrier recombination probability. •The stability of the devices with a PEIE layer is also improved as the device performance can keep within 90 % compared to its original PCE values after 1400-h measurement in a nitrogen-filled glove box without encapsulation.