Mohamed R. Elmorsy

Enhancing photovoltaic performance of DSSCs sensitized with Ru-II complexes by D–π–A configured carbazole based co-sensitizers

Herein, we report the photovoltaic performance studies of four D–π–A configured carbazole based co-sensitizers, P1–4, in DSSCs sensitized with Ru-II complexes, i.e.NCSU-10/N3. The organic co-sensitizers (P1–4) comprise carbazole as a donor scaffold, a phenylene ring as a π-spacer and electron withdrawing functional groups, viz. cyanoacetic acid (P1), rhodanine-3-acetic acid (P1–2), barbituric acid (P3), and thiobarbituric acid (P4) as acceptor/anchoring units. From the results, it is evident that the device fabricated using co-sensitizer P1 carrying cyanoacetic acid, at the concentration of 0.2 mM NCSU-10, exhibited an enhanced photon conversion efficiency (PCE) of 9.19% with a JSC of 21.20 mA cm−2, VOC of 0.658 V and FF of 65.85%, while P3 containing barbituric acid displayed a PCE of 8.75% with a JSC of 22.23 mA cm−2, VOC of 0.671 V and FF of 58.64%, whereas NCSU-10 (0.2 mM) alone displayed a PCE of 8.28% with a JSC of 20.38 mA cm−2, VOC of 0.665 V and FF of 61.09%, but the dyes P2 carrying rhodanine-3-acetic acid and P4 containing thiobarbituric acid showed considerably lower performance. The co-sensitized devices of N3 with P1–4 displayed inferior photovoltaic performance compared to N3 itself, probably due to inefficient suppression of back current. The observed results have thrown new light upon the selection of appropriate and matchable co-sensitizers for improving photovoltaic performance of Ru-II based sensitizers.

Co-sensitization of Ru(II) complex with terthiophene-based D–π–π–A metal-free organic dyes for highly efficient dye-sensitized solar cells: influence of anchoring group on molecular geometry and photovoltaic performance

In this work, we studied the photovoltaic performance of two novel metal-free organic dyes (MR-3 and MR-4) with the molecular motif D–π–π–A carrying the same donor (trimethoxy benzene) and terthiophene (π) units but with different anchoring moieties. MR-3 and MR-4 displayed PCE of 4.54% and 2.38%, respectively. Furthermore, MR-3 co-sensitized with NCSU-10 exhibited improved efficiency of 9.09% than NCSU alone (8.74%). One of the merits in the studied structure motif D–π–π–A was modulating the molecular geometry of the sensitizers and eliminating the steric effect between the donor and π-spacer (terthiophene) to furnish a coplanar molecular structure and to maximize electronic conjugation. In addition, coupling-steric effect precludes effective conjugation and reduces light harvesting as it increases the band gap. To eliminate the steric effect of the aryl moiety at ortho position of 2,4,6-trimethoxyphenyl donor, another conjugated spacer, alkene (CHCH), was inserted between the donor and the π-spacer (terthiophene), which maximized the electron conjugation throughout the coplanar system; the optimized molecular geometry of the dyes was calculated using DFT. Another molecular geometry feature that was studied was the influence of different anchoring groups on coplanarity of the dye structure and consequently the photovoltaic performance. In the case of MR-3, where the anchoring group is based on the cyanoacrylic group, the optimized geometry was found coplanar. However, when rhodanine moiety was used as an anchoring group, the calculated optimized geometry of the dye (MR-4) was not coplanar, which resulted in weak electronic coupling and inferior electronic injection into TiO2 conduction band edge. The inter-relationship between the optimized geometry of the dyes and their photovoltaic performance is discussed.