Abstract
We report the preparation of films of poly(3-hexylthiophene) nanofibers suitable for fabrication of efficient multilayer solar cells by successive deposition of donor and acceptor layers from the same solvent. The nanofibers are obtained by addition of di-tert-butyl peroxide (DTBP) to a solution of P3HT in chlorobenzene. Interestingly, by varying the concentration of DTBP we are able to control both crystallinity and film retention of the spin-cast films. We also investigate the influence of the DTBP-induced crystallization on charge transport by thin-film transistor measurements, and find a more than five-fold increase in the hole mobility of nanofiber films compared to pure P3HT. We attribute this effect to the synergistic effects of increased crystallinity of the fibers and the formation of micrometer-sized fiber networks. We further demonstrate how it is possible to make use of the high film retention to fabricate photovoltaic devices by subsequent deposition of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) from a chlorobenzene solution on top of the nanofiber film. The presence of a relatively large crystalline phase strongly affects the diffusion behavior of PCBM into the P3HT film, resulting in a morphology which is different from that of common bulk heterojunction solar cells and resembles a bilayer structure, as can be inferred from comparison of the external quantum efficiency spectra. However, a high power conversion efficiency of 2.3% suggests that there is still a significant intermixing of the two materials taking place.
Highlights
Organic semiconductors have attracted great interest for photovoltaic applications due to their potential to be manufactured at low cost and on a large variety of substrates.[1,2,3,4] To achieve large-scale production, it is crucial to develop a highly reproducible fabrication procedure that can be incorporated in a roll-to-roll process, and that avoids high temperature treatments to ensure compatibility with exible substrates
Gearba and coworkers reported on thermally cross-linked P3HT by the use of di-tert-butyl peroxide (DTBP), in analogy to a process commonly used in rubber industry to cross-link polyethylene.[30,31,32]
Using UV-vis absorption measurements and grazing-incidence X-ray diffraction (GIXD), we prove an increase in crystallinity upon addition of DTBP to a solution of P3HT in chlorobenzene
Summary
It has been found that thin- lms of regioregular P3HT deposited from solution consist of a semi-crystalline fraction of highly ordered p–p stacks with a typical stacking distance of 3.8 A, and a less ordered, amorphous fraction.[7,8] Several factors are known to in uence this aggregation behavior, including the choice of solvent and the lm preparation method, as well as macromolecular properties of P3HT, such as molecular weight, regioregularity, and polydispersity.[9,10,11,12,13,14]. Gearba and coworkers reported on thermally cross-linked P3HT by the use of di-tert-butyl peroxide (DTBP), in analogy to a process commonly used in rubber industry to cross-link polyethylene.[30,31,32] By adding DTBP directly to a solution of P3HT in chlorobenzene, and by annealing the lms spin-cast from this solution, they observed the lms to become insoluble with increasing peroxide concentration. We are able to control the retention of the lms by adjusting the amount of DTBP added to the solution and make use of this to fabricate efficient solar cells by successively depositing the donor and acceptor layer from the same solvent, using PCBM as an electron acceptor Such cells feature a power conversion efficiency of 2.3%. Since these cells have not been optimized in terms of layer thickness and other processing parameters, we consider there are good prospects for improvement
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
