Photoconduction in polyimide

Photocurrent has been measured in polyimide under exciting radiation in the wavelength range of 7000-2000 A using a sandwich electrode configuration. There are two photocurrent peaks occurring at 4650 A and 3550 A if both the illuminated and nonilluminated electrodes are solid electrodes. The photocurrent in polyimide is insensitive to the polarity and the material of the illuminated electrode, indicating that the photoconduction involves both electrons and holes. When the illuminated electrode is replaced with a finger electrode through which lights can directly illuminate the polyimide surface, then a large photocurrent is observed in the near-UV region (3500-2000 A) which is dependent on both the polarity and the material of the illuminated electrode. The 4650 A and the 3550 A peaks are associated with photogeneration in the polyimide-electrode interfaces, and the photocurrent in the near-UV region using an illuminated finger electrode is due to photoemission from electrodes. By considering the molecular structure of polyimide as a polymeric chain with alternating diamines and dianhydrides acting as donors and acceptors, respectively, it is shown that the photoconduction is probably associated with carrier transport through charge transfer complexes in the polyimide.<
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