Resurgence of DSCs with copper electrolyte: a detailed investigation of interfacial charge dynamics with cobalt and iodine based electrolytes

Deploying earth abundant copper as a redox mediator in dye-sensitized solar cells (DSCs) has been found to be a very promising strategy to achieve higher photovoltage and power conversion efficiencies in full sun (100 mW cm(-2)) and in low/diffuse light conditions. Achieving higher photovoltage without compromising photocurrent helped copper electrolyte attract considerable attention among alternate electrolytes currently employed in DSCs. The very small reorganization energy between Cu(I) and Cu(II) and small molecular size helped copper achieve unit regeneration efficiency, with a driving force as low as 100 mV and a high diffusion coefficient (D-n), leading to better diffusion length (L-n) and charge collection efficiency (eta(cc)). Mass transport issues were also found to be improved for copper electrolytes in comparison with cobalt electrolytes. As it is inert to silver and other electrical contacts used in DSCs and possesses higher mobility even in solid state, copper-based electrolyte is a promising candidate to spearhead the commercialization of dye solar technology. In this regard, a detailed evaluation of internal electron transfer dynamics is highly essential to understand the limiting processes in these devices. In the present study, we performed a comparison between copper, cobalt and iodine electrolytes using the same dye (LEG4), semiconductor (TiO2) and additive concentrations to understand in detail the charge transfer processes leading to higher photoconversion efficiencies and also probe the various deleterious processes taking place in copper devices that provide opportunities to further improve its performance in future

Investigating mass transport and recombination as a function of structural variation in dye-sensitized solar cells employing indole fused heterocyclic organic sensitizers and cobalt electrolytes

Alternate cobalt redox mediator based dye-sensitized solar cells (DSCs) are getting widespread attention taking advantage of their one-electron transfer mechanism compared to the conventional iodide/triiodide electrolyte. In the present study, we used indole fused heterocyclic organic sensitizers having indolo[3,2-b]indole as donor with three different π-spacers [(benzene (IID-1), thiophene (IID-2) and furan (IID-3)] along with cobalt bipyridine derivatives as redox mediators having different peripheral substituents {[Co(bpy)3]3+/2+, [Co(Me2bpy)3]3+/2+, and [Co(t-Bu2bpy)3]3+/2+}. A detailed investigation was carried out to understand the fundamental charge transfer processes and loss mechanism happening at the various interfaces as a function of structural variations in the present dye-electrolyte combinations. Among the investigated systems, higher performance was obtained for the association of furan substituted dye (IID-3) with [Co(t-Bu2bpy)3]3+/2+ electrolyte. The importance of choosing the right combination of sensitizer and electrolyte is critical to realize higher performance in dye-sensitized solar cells particularly while employing organic dyes and alternate metal complex redox electrolytes which was systematically investigated in the present manuscript

Ambient processed perovskite sensitized porous TiO2 nanorods for highly efficient and stable perovskite solar cells

One dimensional (1-D) TiO2 nanorod (NR) scaffold layers are considered to be a superior electron transporting layer (ETL) for perovskite solar cells (PSC) as compared to TiO2 nanoparticles (NP) in relation of morphological and electronic properties. Rutile phase porous TiO2-NR has been grown with different lengths and porosity via the hydrothermal method. Porosity and length of the rods are controlled by varying the reaction time and concentration of the precursor solution. Change in the morphology and their effect on the photovoltaic and charge transport properties are investigated deeply through scanning electron microscopy, current density voltage (J-V) curves and electrochemical impedance spectroscopy (EIS). The synthesized TiO2-NR and NP-TiO2 electrodes are used to fabricate ambient processed PSCs. Compared to the conventional NP-TiO2 based PSC device, the device is prepared with the 350 nm porous TiO2-NR has shown improved power conversion efficiency (14.0%). Such enhancement in photovoltaic performance arises from uniform infiltration of perovskite into the scaffold layer, which enhances the light collection efficiency and increases electron-transport property. Furthermore, the NR based PSC devices have retained 80% of its initial performance even after 50 days of being stored in ambient conditions (relative humidity (RH) - 60%). These results further emphasize the use of 1-D NR as ETL for ambient processed PSC with improved stability

Indolo[3,2-b]indole donor-based D--A dyes for DSCs: investigating the role of -spacers towards recombination

status: publishe

Probing Recombination Mechanism and Realization of Marcus Normal Region Behavior in DSSCs Employing Cobalt Electrolytes and Triphenylamine Dyes

Cobalt based, outer-sphere, one-electron redox shuttles represents an exciting class of alternative electrolyte to be used in dye-sensitized solar cells. The flexibility of redox potential tuning by varying the substituents on peripheral organic ligands renders them the advantage of achieving higher photovoltage. However, higher recombination experienced in these systems by employing diffusion-limited cobalt species serves as a bottleneck which significantly limits attaining higher performance. The focus of the present contribution is to systematically investigate in detail the effect of structural variations and steric hindrance of organic triphenylamine dyes (TPAA4 and TPAA5) which differs in the number and nature of binding groups and peripheral hole accepting units on the recombination reactions and mass transport variations employing two different cobalt electrolytes, [Co₃]^3+/2+ and [Co­(phen)₃]^3+/2+, having variable driving force for recombination. The detailed photovoltaic analysis provides us the information that modification of the architecture of organic dyes plays a decisive role in determining the performance, in particular, employing alternate one-electron outer-sphere redox systems. From our analysis, for both the dyes the charge recombination with the oxidized cobalt species was found to happen in the Marcus normal region which is attributed to the shift in conduction band (CB) that influenced the driving force for recombination. The current observation was quite exciting since the redox systems employed in the present study were previously documented to exhibit Marcus inverted recombination behavior. The impact of structural variations of dyes, change in conduction band, effect of nature of electrolyte species, and its interaction with the semiconductor on the recombination reactions was explored in detail using a range of small and large perturbation techniques

Aggregation induced light harvesting of molecularly engineered D-A-pi-A carbazole dyes for dye-sensitized solar cells

Novel class of metal free organic dyes (CCTh and CCBz) with D-A-pi-A configuration, having carbazole as donor and 3-cyanopyridine as auxiliary acceptor replacing conventional benzannulated heterocycles along with variable pi-linkers were synthesized and used in dye-sensitized solar cells (DSSCs). Both the dyes are having cyanoacrylic acid as the anchoring group with thiophene (CCTh) and phenylene (CCBz) as pi-linkers. The photophysical, electrochemical, theoretical and photovoltaic properties of the dyes were investigated in detail. The absorption spectra of dyes on TiO2 showed broader absorption band for CCTh in comparison to the solution spectra indicating aggregation in solid state. The aggregation studies in varied THF/water fraction indicates J-aggregation for both the dyes. CCTh with thiophene linker showed broader absorption compared to CCBz, and the photovoltaic performance recorded for CCTh directly indicates better light harvesting ability corresponding to the red shifted J-aggregated states. Hence, solar cells fabricated with CCTh gave a power conversion efficiency of 3.39% and CCBz delivered an efficiency of 2.03% under full sun condition. A detailed investigation of device dynamics have been carried out employing charge extraction (CE), intensity-modulated photovoltage spectroscopy (IMVS) and open-circuit voltage decay (OCVD) measurements