Browsing by Author "Misra, Rajneesh"

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Small molecule based N-phenyl carbazole substituted diketopyrrolopyrroles as donors for solution-processed bulk heterojunction organic solar cells
(2016-09-07)
Patil, Yuvraj
;
Misra, Rajneesh
;
Chen, F. C.
;
Sharma, Ganesh D.
;
光電工程學系
We report two acetylene-bridged small molecules DPP5 and DPP6 with low HOMO-LUMO gaps as donors along with PC71BM as an acceptor for the fabrication of solution-processed bulk heterojunction solar cells. After the optimization, i.e. weight ratio of donor to acceptor and surface treatment of the active layer, we achieved overall power conversion efficiencies up to 4.65% (J(SC) = 8.19mA cm(-2), V-OC = 0.98 V and FF = 0.58) and 5.73% (J(SC) = 9.58 mA cm(-2), V-OC = 0.98 V and FF = 0.61), for DPP5:PC71BM and DPP6:PC71BM respectively, which are superior to those for the devices based on as-cast active layers. The significant change in the power conversion efficiency is attributed to the improvement in nanoscale morphology, balanced charge transport and charge collection efficiency, induced through the surface treatment.
Symmetrical and unsymmetrical triphenylamine based diketopyrrolopyrroles and their use as donors for solution processed bulk heterojunction organic solar cells
(2016-01-01)
Patil, Yuvraj
;
Misra, Rajneesh
;
Chen, F. C.
;
Keshtov, M. L.
;
Sharma, Ganesh D.
Two small molecules DPP3 (D-pi-A) and DPP4 (D-pi-A-pi-D) with triphenylamine (TPA) donors and diketopyrrolopyrrole (DPP) acceptors linked with ethyne linkers were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photonic, electronic, thermal and computational properties were investigated. The red shift in the electronic absorption spectra of DPP4 as compared to DPP3 is related to extended conjugation and increased donor-acceptor interaction. We have used DPP3 and DPP4 as electron donors along with PC71BM as an electron acceptor for solution processed bulk heterojunction organic solar cells. The solar cells prepared from DPP3: PC71BM and DPP4: PC71BM (1 : 2) processed from chloroform (CF) exhibit a power conversion efficiency (PCE) of 2.23% (J(sc) = 6.74 mA cm(-2), V-oc = 0.92 V and FF = 0.36) and 3.05% (J(sc) = 8.26 mA cm(-2), V-oc = 0.88 V and FF = 0.42), respectively. The higher PCE of the device with DPP4 compared to DPP3 was demonstrated as to the higher hole mobility and broader IPCE spectra. The devices based on DPP3: PC71BM and DPP4: PC71BM processed with solvent additive (1 v% DIO, 1,8-diiodooctane) showed PCE values of 4.06% and 5.31%, respectively. The device optimization results from the improvement of the balanced charge transport and better nanoscale morphology induced by the solvent additive.