Role of electron blocking and trapping layers in transport characterization of a photovoltaic polymer poly(3-hexylthiophene)

Hole injection and transport in films (300–350 nm) of poly(3-hexylthiophene) (P3HT) were investigated by dark-injection space-charge-limited current (DI-SCLC) technique. For samples with a nominally hole-only configuration of anode/P3HT/Au, the DI current transients depart significantly from the theory, and the signals cannot be used for reliable carrier mobility extraction. The origin of the departure can be attributed to electron leakage from the Au cathode. We outline a means of suppressing electron leakage by inserting an interlayer between the P3HT and the cathode. This interlayer has dual functions of blocking and trapping electrons. Using this interlayer, we obtain well-defined DI-SCLC signals for reliable carrier mobility determination. With a suitable interlayer to suppress undesirable carrier injection and transport, DI-SCLC technique should find broad applications in the transport characterization of narrow gap photovoltaic polymers.

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► DI-SCLC technique is used to probe hole transports in thin films of P3HT.
► Ill-defined signal is observed in hole-only device due to electron leakage.
► Interlayer for blocking and trapping electrons is added to suppress electron leakage.
► With interlayer, well-defined signal is obtained for reliable mobility extraction.