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--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 -spacer and electron withdrawing functional groups, viz. cyanoacetic acid (P-1), rhodanine-3-acetic acid (P1-2), barbituric acid (P-3), and thiobarbituric acid (P-4) as acceptor/anchoring units. From the results, it is evident that the device fabricated using co-sensitizer P-1 carrying cyanoacetic acid, at the concentration of 0.2 mM NCSU-10, exhibited an enhanced photon conversion efficiency (PCE) of 9.19% with a J(SC) of 21.20 mA cm(-2), V-OC of 0.658 V and FF of 65.85%, while P-3 containing barbituric acid displayed a PCE of 8.75% with a J(SC) of 22.23 mA cm(-2), V-OC of 0.671 V and FF of 58.64%, whereas NCSU-10 (0.2 mM) alone displayed a PCE of 8.28% with a J(SC) of 20.38 mA cm(-2), V-OC of 0.665 V and FF of 61.09%, but the dyes P-2 carrying rhodanine-3-acetic acid and P-4 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.