Spectroscopic Studies On Conjugated Polymers

Conjugated polymer semiconductor is an important material of producing organic solar cell and organic light emission diode (OLED), with high PL quantum efficiency and good film quality. Nowadays the study of conjugated polymer has acquired great progress, but it needs more work to study the interchain photoexcitations and conjugated polymer photoexcitations of different chain length to deepen the understanding on its photophysics. In this work, in the film and solution of the model material of 2-methoxy-5-(2-ethylhexyloxy) poly(para-phenylenevinylene) (MEH-PPV) with various chain lengths, we have measured photoluminescence and photoinduced absorption spectroscopy to study their optical properties with which we will analyze the properties and regulatory mechanism of interchain excited states and the regulatory mechanism.In this thesis, we have built up a set of measurement systems for photoluminescence (PL) and photoinduced absorption (PIA) spectroscopies. We have written the control and date collection programs using Labview for automatic measurements. We measured the temperature dependence PL and PIA spectra of MEH-PPV film with different chain lengths at various annealing temperatures. After analyzing the optical processes from the spectra, we got the main conclusions as follows:①The annealing can increase the interchain interactions in film, by enhancing the delocalization of π-electrons then facilitating the formation of interchain excited states; the PL emission around 680 nm at low temperature is due to interchain excimers instead of intrachain excitons for 450 K annealed film; Furthermore, the interchain photoexcitations play crucial roles in the photophysics of MEH-PPV films. The further measurements on PIA spectrum of MEH-PPV films suggest that the interchain photoexciations are also important for the generation of triplet excitons. ②The increasing of conjugated polymers chain length results in aggregation of polymer chain. ③By detecting the polarization effect of photoluminescence and photoinduced absorption spectra, we find that the PL from singlet excitons and excimers as well as the PIA from triplet excitons of MEH-PPV have polarization memory effect, which may originate the nature of quasi one dimensional characteristics of photophysics in conjugated polymers.