Synthesis of POSS-Based Ionic Conductors with Low Glass Transition Temperatures for Efficient Solid-State Dye-Sensitized Solar Cells

Replacing liquid-state electrolytes with solid-state electrolytes has been proven to be an effective way to improve the durability of dye-sensitized solar cells (DSSCs). We report herein the synthesis of amorphous ionic conductors based on polyhedral oligomeric silsesquioxane (POSS) with low glass transition temperatures for solid-state DSSCs. As the ionic conductor is amorphous and in the elastomeric state at the operating temperature of DSSCs, good pore filling in the TiO₂ film and good interfacial contact between the solid-state electrolyte and the TiO₂ film can be guaranteed. When the POSS-based ionic conductor containing an allyl group is doped with only iodine as the solid-state electrolyte without any other additives, power conversion efficiency of 6.29% has been achieved with good long-term stability under one-sun soaking for 1000 h

MOF-Assisted Annealing-Free Crystallization Technology of Perovskites toward Efficient and Stable Perovskite Solar Cells

Although annealing is a commonly used crystallization method for perovskite films in perovskite solar cells (PSCs), the high thermal energy consumption and limitations on flexible devices hinder their further industrial application. We herein propose an annealing-free crystallization technology for perovskite films, assisted by the Zr–metal–organic framework (MOF) interface between SnO2 and the perovskite. It is found that the Zr–MOF interface can accelerate the formation of perovskite intermediates and promote their conversion into perovskite crystals even without annealing. The trap density thus decreases by about one fold, accompanied by significant increases in electron and hole mobilities, resulting in enhanced carrier extraction and suppressed charge recombination. Therefore, the Zr–MOF-based PSC attains a power convention efficiency (PCE) of 20.24%, 2.2 times that (9.26%) of the pristine PSC. Furthermore, the Zr–MOF interface layer can significantly improve the air and thermal stabilities of PSCs. The Zr–MOF-based PSC exhibits 93% of its initial PCE versus 52% for the pristine PSC after 1018 h of storage in air. Additionally, after 360 h of continuous heating at 65 °C, the Zr–MOF-based PSC retains 91% of its initial PCE against 44% for the pristine PSC

POSS-Based Electrolyte for Efficient Solid-State Dye-Sensitized Solar Cells at Sub-Zero Temperatures

To expand the application of solid-state dye-sensitized solar cells (ssDSSCs) to low temperatures, it is necessary to develop new solid electrolytes with low glass transition temperature (<i>T</i>_g). The <i>T</i>_g is regulated by varying the length of alkyl chain that is connected with the nitrogen atom in the imidazolium ring linked to the polyhedral oligomeric silsesquioxane (POSS). The <i>T</i>_g as low as −8.8 °C is achieved with the POSS grafted with methyl-substituted imidazolium. The effect of alkyl group on the conductivity, <i>T</i>_g, and photovoltaic performance has also been investigated. The conductivity and power conversion efficiency increase with the alkyl length, while the <i>T</i>_g first increases and then decreases with the alkyl length. Among the synthesized POSS-based ionic conductors, the POSS grafted with the methyl-substituted imidazolium yields the highest power conversion efficiency of 6.98% at RT due to its highest conductivity, and the efficiency (6.52%) is still good at −4 °C, as its <i>T</i>_g (−8.8 °C) is lower than the working temperature (−4 °C). This finding suggests that the POSS-based solid electrolyte is promising for subzero-temperature applications of ssDSSCs

Electronic-Insulating Coating of CaCO₃ on TiO₂ Electrode in Dye-Sensitized Solar Cells: Improvement of Electron Lifetime and Efficiency

Electronic-insulating coating of CaCO3 on nanocrystalline TiO2 electrode for dye-sensitized solar cells was found to increase both short-circuit photocurrent (Jsc) and open-circuit photovoltage (Voc) remarkably. The significant increase in Jsc is mainly attributed to the remarkably increased dye adsorption resulting from the more basic surface of CaCO3 than TiO2, while the increase in Voc originates from suppression of charge recombination owing to the surface covering of TiO2 with an insulating coating of CaCO3, revealed by intensity-modulated photovoltage spectroscopy. A 15 μm TiO2 (23 nm) nanocrystalline electrode coated with 1 wt % CaCO3, sensitized with N719, produced power conversion efficiency of 10.2%, where N719 is cis-di(thiocyanato)-bis(2,2‘-bipyridyl-4,4‘-dicarboxylate) ruthenium(II), using an antireflective film on the cell surface

Significant Efficiency Improvement of the Black Dye-Sensitized Solar Cell through Protonation of TiO₂ Films

This paper describes the influence of acid pretreatment of TiO2 mesoporous films prior to dye sensitization on the performance of dye-sensitized solar cells based on [(C4H9)4N]3[Ru(Htcterpy)(NCS)3] (tcterpy = 4,4‘,4‘ ‘-tricarboxy- 2,2‘,2‘ ‘-terpyridine), the so-called black dye. The HCl pretreatment caused an increase in overall efficiency by 8%, with a major contribution from photocurrent improvement. It is speculated, from the analysis of incident photon-to-electron conversion efficiency, UV−vis absorption spectra, redox properties of the dye and TiO2, and the impedance spectra of the dye-sensitized solar cells, that photocurrent enhancement is attributed to the increases in electron injection and/or charge collection efficiency besides the improvement of light harvesting efficiency upon HCl pretreatment. Open-circuit photovoltage (Voc) remained almost unchanged in the case of significant positive shift of flat band potential for TiO2 upon HCl pretreatment. The suppression of electron transfer from conduction band electrons to the I3- ions in the electrolyte upon HCl pretreatment, reflected by the increased resistance at the TiO2/dye/electrolyte interface and reduced dark current, resulted in a Voc gain, which compensated the Voc loss due to the positive shift of the flat band. Using the HCl pretreatment approach, 10.5% of overall efficiency with the black dye was obtained under illumination of simulated AM 1.5 solar light (100 mW cm-2) using an antireflection film on the cell surface

In Situ Growth of Co_0.85Se and Ni_0.85Se on Conductive Substrates as High-Performance Counter Electrodes for Dye-Sensitized Solar Cells

We present herein a facile one-step low-temperature hydrothermal approach for in situ growth of metal selenides (Co_0.85Se and Ni_0.85Se) on conductive glass substrates. The as-prepared metal selenides on conductive substrates can be used directly as transparent counter electrodes for dye-sensitized solar cells (DSSCs) without any post-treatments. It is found that graphene-like Co_0.85Se exhibits higher electrocatalytic activity than Pt for the reduction of triiodide. As a consequence, the DSSC with Co_0.85Se generates higher short-circuit photocurrent and power conversion efficiency (9.40%) than that with Pt

Ionic Conductor with High Conductivity as Single-Component Electrolyte for Efficient Solid-State Dye-Sensitized Solar Cells

Imidazolium iodide is an often used component in iodine-based dye-sensitized solar cells (DSSCs), but it cannot operate an efficient DSSC in the absence of iodine due to its low conductivity. For this study, lamellar solid iodide salts of imidazolium or piperidinium with an N-substituted propargyl group have been prepared and applied in solid-state DSSCs. Owing to the high conductivity arising from the lamellar structure, these solid-state ionic conductors can be used as single-component solid electrolytes to operate solid-state DSSCs efficiently without any additives in the electrolyte and post-treatments on the dye-loaded TiO₂ films. With a propargyl group attached to the imidazolium ring, the conductivity is enhanced by about 4 × 10⁴-fold as compared to the alkyl-substituted imidazolium iodide. Solid-state DSSC with the 1-propargyl-3-methylimidazolium iodide as the single-component solid-state electrolyte has achieved a light-to-electricity power conversion efficiency of 6.3% under illumination of simulated AM1.5G solar light (100 mW cm^–2), which also exhibits good long-term stability under continuous 1 sun soaking for 1500 h. This finding paves the way for development of high-conductivity single-component solid electrolytes for use in efficient solid-state DSSCs

Thiophene-Bridged Double D‑π‑A Dye for Efficient Dye-Sensitized Solar Cell

An organic dye containing two D-π-A branches linked with a thiophene unit has been designed and synthesized for efficient dye-sensitized solar cells (DSSCs). As compared to the rod-shape of the single D-π-A analogue dye, the cross shape of the double D-π-A branched dye is favorable for reducing intermolecular interaction and retarding charge recombination. Controlled intensity modulated photovoltage spectroscopy reveals that electron lifetime for the double D-π-A dye-based DSSC is 14-fold longer than that for the corresponding single D-π-A dye-based DSSC. Linking two D-π-A branches with a thiophene unit increases open-circuit photovoltage by 100 mV and short-circuit photocurrent by 4.10 mA cm–2. As a consequence, power conversion efficiency is enhanced by about 2-fold. This work presents a new route to designing sensitizers with high suppression ability of charge recombination toward high-performance DSSCs

NiS₂/Reduced Graphene Oxide Nanocomposites for Efficient Dye-Sensitized Solar Cells

NiS₂ nanoparticles and nanocomposites of NiS₂ with reduced graphene oxide (NiS₂@RGO) have been successfully prepared via a facile hydrothermal reaction of nickel ions and sulfur source in the absence or presence of graphene oxide. NiS₂@RGO nanocomposites exhibit excellent electrocatalytic performance for reduction of triiodide, owing to the improved conductivity and positive synergetic effect between NiS₂ and RGO. As a consequence, the dye-sensitized solar cell with the NiS₂@RGO counter electrode (CE) produces a power conversion efficiency of 8.55%, which is higher than that (7.02%) for the DSSC with the NiS₂ CE, higher than that (3.14%) for the DSSC with the RGO CE, and also higher than that (8.15%) for the DSSC with the reference Pt CE under the same conditions