D-A-D-π-D-A-D type diketopyrrolopyrrole based small molecule electron donors for bulk heterojunction organic solar cells.
Two organic small molecules based on diketopyrrolopyrrole (DPP) units having a D-A-D-π-D-A-D structure denoted as and were synthesized. Their optical and electrochemical properties relevant to organic solar cells were investigated. The wider optical absorption coverage from 450-800 nm, the highest occupied molecular orbital (HOMO) (-5.23 eV and -5.34 eV for and , respectively) and the lowest unoccupied molecular orbital (LUMO) (-3.47 and -3.45 eV for and , respectively) make these small molecules suitable as donors for bulk heterojunction organic solar cells. The bulk heterojunction (BHJ) organic solar cells based on an active layer consists of a blend of these small molecules as donors and PC71BM as an acceptor with an optimized weight ratio of 1 : 2 cast from chloroform (CF) showed overall power conversion efficiencies (PCEs) of 1.98% (with Jsc = 5.38 mA cm(-2), Voc = 0.84 V and FF = 0.42) and 1.85% (with Jsc = 4.56 mA cm(-2), Voc = 0.96 V and FF = 0.42) for and respectively. The relatively high Voc value based on the based device has been attributed to the deeper HOMO of compared to . The optimized  : PC71BM (1 : 2) and  : PC71BM (1 : 2) active layers were subjected to two step annealing (TSA), i.e. thermal annealing and subsequent solvent vapor annealing and the corresponding BHJ organic solar cells showed a PCE of 5.28% (Jsc = 11.53 mA cm(-2), Voc = 0.79 V and FF = 0.58) and 5.52% (Jsc = 10.84 mA cm(-2), Voc = 0.91 V and FF = 0.56), respectively. The enhancement in PCE is mainly due to the improvement in Jsc and FF, related to light absorption in an active layer, a better nanoscale morphology, and an increase in the crystalline nature of the active layer and balanced charge transport, induced by the TSA treatment.
Department of Chemistry, Indian Institute of Technology, Indore (MP) 452020, India.
Yuvraj
Y
Patil
Department of Chemistry, Indian Institute of Technology, Indore (MP) 452020, India.
Rajneesh
R
Misra
Department of Electronics and Communication Engineering, The LNM Institute of Information Technology (Deemed University), Jamdoli, Jaipur (Raj.), 302031, India.
Abhishek
A
Sharma
Department of Physics, The LNM Institute of Information Technology (Deemed University), Jamdoli, Jaipur (Raj.), 302031, India.
Ganesh D
GD
Sharma