Highly Efficient One-Dimensional ZnO Nanowire-Based Dye-Sensitized Solar Cell Using a Metal-Free, D-π-A-Type, Carbazole Derivative with More than 5% Power Conversion

Hydrothermally grown one-dimensional ZnO nanowire (1D ZnO NW) and a newly synthesized metal-free, D-pi-A type, carbazole dye (SKI) sensitizer-based photovoltaic device with a power efficiency (PCE) of more than 5% have been demonstrated by employing the cobalt tris(2,2'-bipyridyl) redox shuttle. A short-circuit current density (J(sc)) of similar to 12.0 mA/cm(2), an open-circuit voltage (V-oc) of 719 mV, and a fill factor (FF) of similar to 65% have been afforded by the ID ZnO NW-based dye-sensitized solar cell (DSSC) incorporating [Co-(bpy)(3)](3+/2+) complex as the one-electron redox mediator. In contrast, the identical DSSC with traditional 13-A- electrolyte has shown a Jsc 12.2 mA/cm(2), a V-oc approximate to 629 mV, and a FF approximate to 62%, yielding a PCE of similar to 4.7%. The persuasive role of the inherent superior electron transport property of ID ZnO NWs in enhancing the device efficiency is evidenced from the impoverished performance of the DSSCs with photoanodes fabricated using ZnO nanoparticles (NPs). The DSSCs having ZnO NP-based photoanodes have achieved the PCEs of similar to 3.6% and similar to 3.2 using cobalt- and iodine-based redox electrolytes, respectively. The electronic interactions between the SKI sensitizer and ZnO (NVVs and NPs) to induce the photogenerated charge transfer from SKI to the conduction band (CB) of ZnO are evidenced from the significant quenching of photoluminescence and exciton lifetime decay of SKI, when it is anchored onto the ZnO architectures. The energetics of the SKi dye molecule are estimated by combining the spectroscopic and electrochemical techniques. The electronic distributions of SKI dye molecule in its HOMO and LUMO energy levels are interpreted using density functional theory (DFT)-based calculations. The electron donor-pi linker-acceptor (D-pi-A) configuration of SKI dye provides an intramolecular charge transfer within the molecule, prompting the electron migration from the carbazole donor to cyanoacrylic acceptor moiety via the oligo-phenylenevinylene linker group. The D-pi-A-mediated electron movement witnesses the favorable photoexcited electron transfer from the LUMO of SKi dye to the CB of ZnO through the carboxyl anchoring group.