Influence of 4-tert-butylpyridine/guanidinium thiocyanate co-additives on band edge shift and recombination of dye-sensitized solar cells: experimental and theoretical aspects

Effect of Iodide-Based Organic Salts and Ionic Liquid Additives in Dye-Sensitized Solar Cell Performance

The use of ionic liquid and organic salts as additives for electrolyte systems in dye-sensitized solar cells have been widely described in recent years. The tunability of their physical-chemical properties according to the cation-anion selection contributes toward their high efficiencies. For this purpose, several iodide-based organic salts including imidazolium, picolinium, guanidinium and alkylammonium cations were tested using acetonitrile/valeronitrile electrolytes and their photovoltaic parameters were compared. A best efficiency of 4.48% (4.15% for the reference) was found for 1-ethyl-2,3-dimethylimidazolium iodide ([C2DMIM]I) containing electrolyte, reaffirming the effectiveness of these additives. 4-tertbutylpyridine was included into the formulation to further improve the performance while determining which iodide salts demonstrate the highest synergy with this additive. [C2DMIM]I once again proved to be the superior additive, achieving an efficiency of 6.48% (6% for the reference). Electrochemical impedance spectroscopy was employed to elucidate the effects of the various additives, demonstrating the relevance of the counter electrode resistance on device performance. Finally, several computational descriptors for the cationic structures were calculated and correlated with the photovoltaic and resistance parameters, showing that properties related to polarity, namely relative positive charge, molecular polarizability and partition coefficient are in good agreement with the counter-electrode resistance.

Poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) and polyvinylidene fluoride blend doped with oxydianiline-based thiourea derivatives as a novel and modest gel electrolyte system for dye-sensitized solar cell applications

Unique symmetrical thiourea derivatives with an oxydianiline core were synthesized using cost-effective and simple methods. A new gel electrolyte system was prepared using these thiourea additives along with a highly conductive PEG–PPG–PEG block copolymer, PVDF, and an iodide/triiodide redox couple. The PEG units present in the electrolyte are well-known for their intense segmental motion of ions, which can degrade the recombination rate and favour the charge transfer. The thiourea additives interacted well with the redox couple to limit iodine sublimation and their adsorption induced a negative potential shift for TiO₂. The highest efficiency attained by utilizing such gel polymer electrolytes was 5.75%, especially with 1,1′-(oxybis(4,1-phenylene))bis(3-(6-methylpyridin-2-yl) thiourea) (OPPT), under an irradiation of 100 mW cm⁻². The electrochemical impedance spectroscopy, UV-vis absorption spectroscopy, differential scanning calorimetry, and FTIR spectroscopy data of such gel polymer electrolytes favoured the PCE order of the additives used in DSSCs. The improvement in the DSSC performance with symmetrical thioureas having electron-rich atoms was practically attributed to the reduction of back electron transfer, dye regeneration, and hole transport.

A unique gel polymer electrolyte was prepared using PVDF and PEG–PPG–PEG block copolymer with I⁻/I₃⁻ for DSSC application. This is a cost-effective method used for the synthesis of thiourea additives. The GPE with OPPT thiourea additive achieved a good efficiency of 5.7%.

Organic dye-sensitized solar cells containing alkaline iodide-based gel polymer electrolytes: influence of cation size

The electrolyte used in dye-sensitized solar cells (DSSCs) plays a key role in the process of current generation, and hence the analysis of charge-transfer mechanisms both in its bulk and at its interfaces with other materials is of fundamental importance. Because of solvent confinement, gel polymer electrolytes are more practical and convenient to use with respect to liquid electrolytes, but in-depth studies are still necessary to optimize their performances. In this work, gel polymer electrolytes of general formulation polyacrylonitrile (PAN)/ethylene carbonate (EC)/propylene carbonate (PC)/MI, where M⁺ is a cation in the alkaline series Li-Cs, were prepared and used in DSSCs. Their ionic conductivities were determined by impedance analysis, and their temperature dependence showed Arrhenius behavior within the experimental window. FT-IR studies of the electrolytes confirmed the prevalence of EC coordination around the cations. Photo-anodes were prepared by adsorbing organic sensitizer D35 on nanocrystalline TiO₂ thin films, and employed to build DSSCs with the gel electrolytes. Nanosecond transient spectroscopy results indicated a slightly faster dye regeneration process in the presence of large cations (Cs⁺, Rb⁺). Moreover, a negative shift of TiO₂ flat-band potential with the decreasing charge density of the cations (increasing size) was observed through Mott-Schottky analysis. In general, results indicate that cell efficiencies are mostly governed by photocurrent values, in turn depending on the conductivity increase with cation size. Accordingly, the best result was obtained with the Cs⁺-containing cell, although in this case a slight reduction of photovoltage compared to Rb⁺ was observed.

New D–π–A dyes incorporating dithieno[3,2-b:2′,3′-d]pyrrole (DTP)-based π-spacers for efficient dye-sensitized solar cells

Bulky substituents on the N-position of the DTP spacer optimize the photovoltaic performances of DSSCs.