The Bulk Hetero-junction Polymer/Carbon Nanotubes Organic Photodetectors

During the fast development of nanotechnology, carbon nanotubes have been successfully applied into the polymer as the electron acceptor. However, the main obstacles using carbon nanotubes in the composite films are as follows.1) The wettability of carbon nanotubes.2) The dispersion in the blend films. Nowadays, these problems cannot be solved by polar or nonpolar solvent, but the functionalization of carbon nanotube can relies it. Once the carbon nanotubes can be evenly dispersed in the solution, the nanotubes network will be completed, which is benefit for the transfusion of charge. On the otherwise, the functionalization of carbon nanotubes also has disadvantage. The advert effect makes the nanotubes lose π conjunction. If the carbon nanotubes are dispersed in the polar solvent such as water, the final blend films will be easy to wet. The advantage of functionalization of carbon nanotubes is that there is no obstacle for the π conjunction in the polymer films. Apart from that, the amount for addition of group is very small, which is easy to eradicate. Under this condition, Carbon nanotubes can be soluble due to the non-conjuncted group.In this paper, we study the structure and optical properties incorporating small amount of carboxylic multi-walled carbon nanotubes. The conclusion has been obtained using the AFM, TEM, UV-Vis and FTIR, which is useful for the organic photovoltaic.1) the effect of crystallity for P3HTWe choose the carboxylic multi-walled carbon nanotubes as the acceptor in order to study the change of structure. The crystallity of P3HT is enhanced after adding the carbon nanotubes with the content of multi-walled carbon nanotubes. This phenomena is proved by the XRD, UV-Vis and AFM. It is clearly shown that the chains of P3HT make curls around carbon nanotubes.2) the effect of optical properties for P3HTVia the steady Photoluminescence and time-resolved Photoluminescence, we can clearly observed the decrease of life-time after adding carbon nanotubes resulting from the charge transfer between the P3HT and carbon nanotubes. It is demonstrated by the quenching of steady Photoluminescence and the life-time decrease of time-resolved Photoluminescence. We found the intensity of 0-0 peak increase with the content of carbon nanotubes due to the formation H-type to J-type of P3HT.3) the performance of organic photodetectors using carbon nanotubesThe photocurrent of P3HT/carbon nanotubes is enhanced compared to the pure P3HT organic photodetectors, which is resulted by the increase of exciton fission incorporating the carbon nanotubes. It is illustrated by the enhancement of photo response under the light. On the other aspect, the dark current of device increase because of the good conductivity of carbon nanotubes, which is not benefit for the application.In order to further study the optical properties of P3HT adding carbon nanotubes, we choose the different diameter carbon nanotubes to mix with the P3HT and study the films.1) the structure of carbon nanotubes/polymer filmsThe single-and multi-walled carbon nanotubes are chosen to intermix with P3HT. It is shown the single-walled carbon nanotubes/P3HT films generate more obvious red shift indicating better crystallity compared to the multi-walled carbon naotubes/P3HT films. Besides, the dispersion of single-walled carbon nanotubes is found to be better than that of multi-walled carbon nanotubes through TEM. We can clearly observed the chains of P3HT parcel around the carbon nanotubes resulting in the red shift of absorption peak.Furthermore, it is observed that the intensity of PL 0-0 peak in the composite films increases after adding the carbon nanotubes resulted by the formation of H-type to J-type compared to the previous work. Apart from that, the intensity of single-walled carbon nanotubes/P3HT is stronger than that of multi-walled carbon nanotubes/P3HT films indicating the single-walled carbon nanotubes can easily affect the crystallity of P3HT. This phenomena is consistent with the former experiments. Through the TCSPC, the lifetime decreased after adding the carbon nanotubes due to the better charge transfer between the carbon nanotubes. Furthermore, the decrease for lifetime of single-walled carbon nanotubes is faster than corresponding lifetime of multi-walled carbon nanotubes.