Pyrene Based Donor-Acceptor Conjugated Polymers for Photovoltaic Applications

Photovoltaic devices have emerged as a promising and efficient technology to address rising global energy demands as the current energy source, which depends on fossil fuels is running out. This technology has the ability to directly convert sunlight to electricity. Inorganic photovoltaic devices exhibit relatively high power conversion efficiencies from 8 to 29%. However, the high cost of these devices has impeded their widespread usage. Intensive research has been done in order to find different approaches to explore less expensive materials to maintain a technology path for photovoltaic devices. Organic photovoltaic devices based on conjugated polymers have gained a large amount of attention from researchers and academicians owing to their potential characteristics when compared with inorganic solar cells. The potential characteristics of organic photovoltaic devices are as follows: they are economical, light weight, and their roll to-roll production is fast and inexpensive. Several types of π-conjugated polymers have been synthesized and applied as electron donor materials in organic photovoltaic devices, either as homopolymers or alternating donor-acceptor copolymers.
In this project, different type of donor-acceptor conjugated polymers, consisting of pyrene as the electron donor and benzothiadiazole or thieno[3,4-c]pyrrole-4,6-dione as the electron acceptor, have been prepared via palladium catalysed cross-coupling reactions such as Stille or direct arylation. The purity and identity of all monomers were confirmed by 1H and 13C NMR spectroscopy, GC-MS and elemental analysis. The structures of all synthesised polymers have been confirmed by 1H NMR spectroscopy and elemental analysis. The thermal, optical and electrochemical properties of all polymers have been investigated using TGA, UV-vis, CV and XRD in order to evaluate their suitability for application in organic photovoltaic devices. The optical band gap of all polymers ranged between 1.76 and 2.06 eV. Bulk heterojunction devices were fabricated from all polymers using PC70BM as the electron acceptor. Preliminary studies indicated that the power conversion efficiencies of the polymers ranged from 0.33 and 2.06 %.