Mimicking the Heteroleptic Dyes for an Efficient 1D-ZnO Based Dye-Sensitized Solar Cell Using the Homoleptic Ruthenium(II) Dipyridophenazine Complex as a Photosensitizer

Abstract

Mimicking the properties of heteroleptic ruthenium dyes, a dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylic acid (dppz-COOH) ligand based homoleptic complex, Ru(dppz-COOH)2(NCS)2, with a molar extinction coefficient of 14.3 × 103 M–1 cm–1 has been demonstrated as an efficient photosensitizer for the one-dimensional (1D) ZnO nanowire (NW) and ZnO nanoparticle (NP) based dye-sensitized solar cells (DSSCs) employing cobalt complexes as the redox mediators. The as-synthesized homoleptic dye achieves an intense metal-to-ligand charge transfer (MLCT) absorption band throughout the visible region due to the optimal π-conjugated dipyridophenazine ring extension and concomitantly retains an efficient dye loading tendency as confirmed by the chemisorption results. Electron density distributions of the frontier molecular orbitals obtained from density functional theory (DFT) indicated a characteristic MLCT transitions of the dye molecule as well as a favorable charge transfer feasibility from the lowest unoccupied molecular orbital of the dye to the conduction band of ZnO through the anchoring carboxylic groups. All the fabricated DSSCs were characterized by measuring the current density–voltage, incident photon-to-current conversion efficiency, and the electrochemical impedance spectroscopy (EIS). The results establish an efficient light harvesting property of the dye and explain the significance of faster charge transport through 1D ZnO NWs in enhancing the device efficiency in contrast to its ZnO NP counterpart. In consort with the interfacial charge transfer and recombination processes occurring in the DSSCs, EIS analysis likewise provides an insight into the prolonged photoinduced electron lifetime for the cells composed of ZnO NWs as compared to ZnO NPs.

Noble metal-free counter electrodes utilizing Cu2ZnSnS4loaded with MoS2for efficient solar cells based on ZnO nanowires co-sensitized with CuInS2–CdSe quantum dots

“…Notably, FESEM images of CZTS-MoS 2 show a relatively more agglomerated feature of the microspheres in contrast to CZTS counterparts. In earlier reports, [24][25][26][27] we have already established the significant role of similar ZnO NWs to improve the efficiency of QDSCs and DSCs. 59 To further elucidate the elemental composition of CE materials, energy dispersive X-ray spectroscopy (EDS) maps of bare CZTS and CZTS-MoS 2 are recorded.…”

“…However, in this work, unlike previously used SILAR method, 26 we have adapted an EPD route to deposit QDs onto ZnO NWs. 24,25 Crystalline nature of CuInS 2 QDs is also evidenced from their well-defined lattice planes observed in the HRTEM image as shown in Figure S6d To confirm the loading of CuInS 2 and CdSe QDs onto ZnO NWs, TEM analysis of a co-sensitized photoanode is carried out. It is confirmed by FESEM images of the photoanodes (Figures 6b-d), which clearly show the retention of 1D geometry of ZnO NWs even after the loading of QDs are performed under the external bias of ~150 mV cm −1 for CuInS 2 and ~0.60 mA cm −1 for CdSe.…”

“…20 The use of such 1D structures are advantageous as they possess a single or quasi-single crystalline geometry, which facilitates a unidirectional pathway for facile charge transport, an increased electron diffusion length, and reduced grain-boundary scattering. [24][25][26][27] Especially, epitaxially grown 1D ZnO NW based pathways promoting the transport and a rapid collection of charge carriers injected from the sensitizers. 21,22 In essence, a superior electron mobility (ZnO ≈ 200-1000 cm 2 .V.s −1 , TiO 2 ≈ 0.1-4 cm 2 .V.s −1 ), band offsets similar to that of TiO 2 , higher crystallinity, lesser grain boundary, and readily tunable morphologies with benchtop synthetic routes make ZnO a prime alternate to traditional TiO 2 .…”

Transition metal complex redox shuttles for dye-sensitized solar cells

“…67 The results showed that there is a constructive relationship between V oc and the number of n-hexylthiophene units, bulkiness of the appendage group in the donor segment, and shorter alkyl chains in the thiophene linker moiety. 83 The ZnO NW based DSSCs afforded a higher ߟ value of ∼ 5.9% and ∼ 5.6% employing [Co(bpy) 3 ] 2+/3+ and [Co(phen) 3 ] 2+/3+ complexes, respectively. Also, a series of efficient carbazole based sensitizers, JM1-JM3 76 and JK-318-JK320 77 were tested for DSSCs in the presence of Co-based redox mediators.…”

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

“…Complexes of dppz have been studied with respect to use in solar cell devices [21][22][23] and have been used in organic light emitting diodes. [24][25][26][27][28][29] However, most prominently, it is known to undergo the light-switch effect, whereby the complexes are non-emissive in aqueous solutions and become emissive in organic solvents or in the presence of DNA.…”