Geminate recombination of long-lived electron-hole pairs in doped carbazole-containing amorphous molecular semiconductors

Abstract

This paper reports an investigation into the features of geminate recombination of long-lived electron-hole pairs in films of poly(N-epoxypropylcarbazole) (PEPC) containing intramolecular charge transfer compounds as centers of photogeneration of charge carriers carried out by measuring the attenuation kinetics of isothermal recombination luminescence over a wide range of temperatures (4.2–300 K) for times t>1 s, along with the kinetics of photoinduced EPR signals. A study is made of how the presence of a potential barrier to the reverse transition of carriers to the recombination center and the initial triplet state of the charged pairs affects the geminate recombination. It is established that the kinetics of isothermal recombintation luminescence attenuation follow the law I(t)∝t −m for the times under study, where m takes values from 0.65 to 1.05. The first observations of a nonmonotonic change in m with temperature are reported (m passes through a minimum at a certain temperature), and a mechanism is proposed for recombination of charged pairs in PEPC containing intramolecular charge-transfer compounds as an explanation for this phenomenon.