For organic solar cells: exciton generation, exciton diffusion, charge transfer, and charge transport of a photoactive layer are the important factors in photocurrent generation. In this thesis, we blend small molecular material tris(8-hydroxyquinoline)aluminum (Alq3) into poly [ 2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene ]:short-length carbon nanotubes (MEH-PPV:SLCNTs) films to increase the light absorption, in the range of 300 to 450 nm, and hence increase the exciton generation. The comparison of the photoluminescence (PL) of a donor with that of the Donor-Acceptor composite provides an important and simple method to detect the charge transfer phenomenon. Furthermore, the degree of photoluminescence quenching may be representative of the efficiency of charge transfer. [1-6] Using this concept and method, we obtain that at the mix ratio of 1:0.5 (MEH-PPV:SLCNTs) by weight, 33 wt.% SLCNTs, probably have the maximum of charge transfer efficiency. To further check that at this concentration might have the maximum efficiency of the charge transfer, we also used time-resolved fluorescence spectrometer to measure the fluorescence lifetime of MEH-PPV. The shortest MEH-PPV fluorescence lifetime of 0.15 ns at 33 wt.% SLCNTs corresponds with our conjecture. For simplicity to discuss next experiment results, we make two assumptions at this mix ratio: (1) The efficiency of the charge transfer process is very high, so the competing processes can be neglected. Because of the forward electron transfer process occurs in the sub-picosecond time domain; (2) The exciton diffusion efficiency is approximately unity in the bulk heterojunction photoactive layer. Based on this assumption, the higher degree of photoluminescence quenching of MEH-PPV:Alq3 and MEH-PPV:Alq3:SLCNTs system demonstrates blending alq3 into MEH-PPV:SLCNTs films maybe can increase the charge photogeneration. The PL and UV/VIS absorption spectra are employed to examine the energy transfer process between Alq3 and MEH-PPV. When MEH-PPV:Alq3 films are excited at the wavelength of 380 nm which is in the main absorption region of Alq3, the increase in PL intensity of MEH-PPV at 577nm and the absent emission spectra of Alq3 illustrates Alq3 transfer its energy to MEH-PPV. By scanning electron microscopy, we observed that the surface pinholes became less than that of MEH-PPV films. This result suggests the devices utilizing the MEH-PPV:Alq3 composites as electron donor materials may have smaller electrode contact resistance. From all above the experiment data, we believe using MEH-PPV:Alq3:SLCNT as a photoactive layer perhaps can enhance the device performance.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0719106-233414 |
| Date | 19 July 2006 |
| Creators | Chen, Sheng-wei |
| Contributors | Wen-yao Huang, Chao-kuei Lee, Yu-kai Han, Mei-ying Chang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0719106-233414 |
| Rights | not_available, Copyright information available at source archive |
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