Funnel shaped molecules containing benzo/pyrido[1,2,5]thiadiazole functionalities as peripheral acceptors for organic photovoltaic applications?

RSC Advances Pub Date: 2016-07-06 DOI: 10.1039/C6RA06616J

Abstract

A series of four novel funnel shaped triphenylamine core derivatized materials with various combinations of 3,6-di-tert-butyl-9H-carbazole as donors and benzo/pyrido[1,2,5]thiadiazole as peripheral acceptors were designed, synthesized and characterized. Optical and electrochemical studies revealed that increasing acceptor strength in the structure leads to a bathochromic shift in their absorption profile and stabilizes the lowest unoccupied molecular orbital (LUMO) energy level. Enhancement in the intensity of an intramolecular charge transfer transition with synergistic downshift of the highest occupied molecular orbital (HOMO) and LUMO levels was observed by increasing the number of acceptor units. Thermogravimetric analyses (TGA) indicated that the materials containing pyrido[1,2,5]thiadiazole (PTD) acceptor functionality have excellent thermal stability compared to the materials containing benzo[1,2,5]thiadiazole (BTD) functionality. The measurement of glass transition temperature (Tg) corroborated TGA results and the values were found to be in the range of 148–198 °C. X-ray analyses indicated that more twist in the structure leads to absorption in the high energy region and varying the number of electron donor and acceptor groups has an impact on the modulation of frontier energy levels. A power conversion efficiency of 2.21% for the molecule with PTD as an acceptor and bis-carbazole as donor was achieved for the preliminary photovoltaic devices under simulated AM 1.5 illumination (100 mW cm?2).

Graphical abstract: Funnel shaped molecules containing benzo/pyrido[1,2,5]thiadiazole functionalities as peripheral acceptors for organic photovoltaic applications
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