title: A dithieno[3,2-b:2',3'-d]pyrrole based, NIR absorbing, solution processable, small molecule donor for efficient bulk heterojunction solar cells.
abstract: A novel, NIR absorbing organic small molecular donor material denoted as ICT3 with an A-D-D-D-A architecture having dithieno[3,2-b:2',3'-d]pyrrole (DTP) and butylrhodanine as donor and acceptor moieties, respectively, is synthesized and its thermal, photophysical, electrochemical and photovoltaic properties are explored. ICT3 has excellent stability over a broad range of temperatures with a decomposition temperature (Tdcorresponds to 5% weight loss) of 372 °C, soluble in most common organic solvents (solubility up to 30 mg mL-1) and suitable for solution processing during device fabrication. ICT3 has broad (520-820 nm) and intense visible region absorption (molar excitation coefficient is 1.69 × 105mol-1cm-1) and has suitable HOMO and LUMO energy levels with the [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) acceptor for efficient exciton dissociation and charge transfer. Bulk heterojunction solar cells (BHJSCs) with an indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/ICT3:PC71BM/poly(9,9-bis(3'-(N,N-dimethylamino)propyl)fluorene-2,7-diyl)-alt-(9,9-dioctylfluorene-2,7-diyl) (PFN)/aluminium (Al) structure are fabricated and the BHJSCs with the active layer as cast from chloroform solution displayed a power conversion efficiency (PCE) of 3.04% (JSC= 8.22 mA cm-2, VOC= 0.86 V and FF = 0.43). Annealing the active layer significantly improved the PCE of these BHJSCs. While thermal annealing of the active layer improved the PCE of the BHJSCs to 4.94%, thermal followed by solvent vapour annealing enhanced the PCE to 6.53%. X-ray diffraction and atomic force microscopy analyses are carried out on the active layer and these results revealed that annealing treatment improves the crystallinity and nanoscale morphology of the active layer, enriches the device exciton generation and dissociation efficiency, charge transport and collection efficiency and reduces carrier recombination. The observed higher PCE (6.53%) of the BHJSCs having ICT3 with a DTP donor moiety broadens the scope to develop new, efficient DTP based small molecular donor materials for BHJSCs.
authors.affiliation: Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India. chereddynarendra@gmail.com jrao@iict.res.in.
authors.forename: Manohar Reddy
authors.initials: MR
authors.lastname: Busireddy
authors.affiliation: Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India. chereddynarendra@gmail.com jrao@iict.res.in.
authors.forename: Venkata Niladri
authors.initials: VN
authors.lastname: Raju Mantena
authors.affiliation: Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India. chereddynarendra@gmail.com jrao@iict.res.in.
authors.forename: Narendra Reddy
authors.initials: NR
authors.lastname: Chereddy
authors.affiliation: Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India.
authors.forename: Balaiah
authors.initials: B
authors.lastname: Shanigaram
authors.affiliation: Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India.
authors.forename: Bhanuprakash
authors.initials: B
authors.lastname: Kotamarthi
authors.affiliation: Department of Physics, The LNM Institute of Information Technology, Jamdoli, Jaipur, India. gdsharma273@gmail.com.
authors.forename: Subhayan
authors.initials: S
authors.lastname: Biswas
authors.affiliation: Department of Physics, The LNM Institute of Information Technology, Jamdoli, Jaipur, India. gdsharma273@gmail.com.
authors.forename: Ganesh Datt
authors.initials: GD
authors.lastname: Sharma
authors.affiliation: Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India. chereddynarendra@gmail.com jrao@iict.res.in and AcSIR, CSIR-Indian Institute of Chemical Technology, Hyderabad-500007, India.
authors.forename: Jayathirtha Rao
authors.initials: JR
authors.lastname: Vaidya