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Indexed by:Journal Papers

Date of Publication:2021-01-10

Journal:ACTA POLYMERICA SINICA

Volume:51

Issue:4

Page Number:338-345

Key Words:Poly(3-hexylthiophene); Annealing; Film thickness; Film morphology; Photodetector

Abstract:Poly(3-hexylthiophene) (P3HT) with good electronic transmission capacity is one of promising material for organic photodetector. Compared with organic solar cells, the research of photodetector based on P3HT is deficient, especially in how to improve the light absorption efficiency and electronic transmission ability of active layer. Here, bulk heterojunction photodetectors with a structure of ITO/PEDOT:PSS/P3HT:PC61BM/C-60/Al were prepared by using P3HT as a donor and fullerene derivative (PC61BM) as an acceptor. The change of active layer thickness plays an important role in the effective transfer of photogenerated charge to the electrode. Although increasing the thickness of active layer can increase the light absorption efficiency, it may also lead to the recombination of electrons and holes in the process of long distance transmission. In addition, annealing condition is the key to the film forming process. Adjusting the annealing temperature can control the self-assembly of active layer, thus obtaining the ideal nano-size phase separation structure and reducing the recombination probability of photoexcitons. Therefore, the active layer thickness in P3HT devices varied at 120, 160, 180 and 200 nm and the devices were annealed at 100, 120, 130, 140 and 150 degrees C in order to probe the effect of these variables on photodetector performance. It was found that the device with a 180-nm thick active layer, after being annealed at 150 degrees C, exhibited the maximal responsivity of 268 mA/V at 550 nm and more than 200 mA/W in the wavelengths of 470 - 610 nm under the bias of -2 V. Furthermore, the same device showed a linear dynamic range of 95 dB after annealing at 120 degrees C. Our study demonstrates that the thickness of active layer is of great importance to the light absorption efficiency and the device performance, while the annealing treatment can significantly affect the morphology of active layer, as evidenced by AFM study, which reduces the recombination probability of holes and the electrons and thus improves the photodetector performance.