Internal Electric Field and Photocurrent of Polymer/Perylene Heterojunction Solar Cell

The internal electric field in a heterojunction solar cell made of poly(5-(2'-ethylhexyloxy)-2-methoxy-1,4-phenylenevinylene) (MEH-PPV) as a donor and 3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) as an acceptor is studied by electroabsorption (EA). The 1ω-EA signal detected at the fundamental electric-field-modulation frequency ω comes from the bulk of the film for MEH-PPV but from the interface of the film for PTCBI. The bias dependence of the bulk electric field for MEH-PPV is correlated with that of the photocurrent generated by MEH-PPV excitation, indicating that the electric field has an essential role in carrier photogeneration. An analysis of the photocurrent action spectrum indicates that the photocurrent-active region in the MEH-PPV layer changes its location depending on the applied bias voltage. This suggests that the region of strong electric field in the MEH-PPV layer changes its location along with the active layer.