SEMICONDUCTING POLYMERS (AS DONORS) AND BUCKMINSTERFULLERENE (AS ACCEPTOR) - PHOTOINDUCED ELECTRON-TRANSFER AND HETEROJUNCTION DEVICES

Experimental results on the metastable, reversible, photoinduced electron transfer between semiconducting polymers and buckminsterfullerene are reviewed. Photoinduced absorption (photoexcitation spectroscopy), steady state and picosecond time-resolved photoluminescence and light-induced electron spin resonance measurements are summarized as experimental evidence for photoinduced electron transfer. Comparative studies with different semiconducting polymers as donors demonstrate that in the degenerate ground state the polymer's soliton excitations form before the electron transfer can occur, thereby inhibiting charge separation. In non-degenerate ground state systems, photoinduced electron transfer occurs in less than 10(-12) s, quenching the photoluminescence as well as the intersystem crossing. The importance of electron-phonon coupling in these low-dimensional semiconductor polymers, resulting in structural relaxation upon photoexcitation, is proposed to contribute to the stabilization of the charge-separated state. Utilizing thin films of the semiconducting polymer (donor) and buckminsterfullerene (acceptor) to form a heterojunction interface, we fabricated diode bilayers which functioned as photodiodes and as photovoltaic cells. The results are discussed in terms of opportunities for solar energy conversion, for photodiode detector devices and for a variety of other applications which use photoinduced intermolecular charge separation.