Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions

TLDR

The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. The authors present a novel phase‑separated polymer blend composed of MEH‑PPV as donor and CN‑PPV as acceptor. The blend is formed by phase separation of these polymers, enabling efficient electron–hole separation. Photoluminescence and electroluminescence quenching in the blend confirms rapid charge separation, and diodes fabricated from the composite achieve 5 % carrier collection and 0.9 % energy conversion—about 20‑fold and 100‑fold higher than pure MEH‑PPV and CN‑PPV, respectively—while reverse bias boosts photosensitivity to 0.3 A W⁻¹ and quantum yield to 80 % electrons per photon, approaching inorganic semiconductor performance.

Abstract

The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. We describe a novel phase-separated polymer blend (composite) made with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], MEH-PPV, as donor and cyano-PPV, CN-PPV, as acceptor. The photoluminescence and electroluminescence of both component polymers are quenched in the blend, indicative of rapid and efficient separation of photogenerated electron-hole pairs with electrons on the acceptor and holes on the donor. Diodes made with such a composite semiconducting polymer as the photosensitive medium show promising photovoltaic characteristics with carrier collection efficiency of 5% electrons/photon and energy conversion efficiency of 0.9%, ∼20 times larger than in diodes made with pure MEH-PPV and ∼100 times larger than in diodes made with CN-PPV. The photosensitivity and the quantum yield increase with reverse bias voltage, to 0.3 A/W and 80% electrons/photon respectively at −10 V, comparable to results obtained from photodiodes made with inorganic semiconductors.