Highly Efficient Bifacial Dye-Sensitized Solar Cells Employing Polymeric Counter Electrodes

Advances in materials and devices for smartlife photovoltaic innovations

The rapid development of photovoltaic (PV) technologies is expanding their applications beyond conventional outdoor energy harvesting into innovative smart-life energy solutions. This review examines the most recent progress in materials and device designs for various emerging PV systems, particularly in indoor and low-light environments, semitransparent devices, and flexible, wearable applications. These advancements have great potential to support autonomous smart life, enhance the energy efficiency of building-integrated solutions, and improve wearable technologies. Despite these gains, challenges such as improving efficiency, durability, scalability, and affordability remain, requiring interdisciplinary collaboration and further research to fully unlock PV technologies' role in sustainable, energy-efficient smart life.

Hydroxycinnamic acid derivatives for UV-selective and visibly transparent dye-sensitized solar cells

Naturally abundant dyes are very attractive for the development of dye-sensitized solar cells (DSSCs). Hydroxycinnamic acid derivatives, such as caffeic acid (CA), ferulic acid (FA), and p-coumaric acid (PA), were considered for the selective harvesting of ultraviolet A (UVA) (315-400 nm) photons. Their spectroscopic and electrochemical properties were investigated both theoretically and experimentally. They were further successfully adopted as photosensitizers in UV-selective and visibly transparent DSSCs, which exhibited a power conversion efficiency of 0.22-0.38% under AM (air mass) 1.5G (global) illumination (100 mW/cm²) and 3.40-3.62% under UVA irradiation (365 nm, 115.22 mW/cm²), with a corresponding visible light transmittance (VLT) of 49.07-43.72% and a general color rendering index (R_a) of 93-90.

Stable Cobalt-Mediated Monolithic Dye-Sensitized Solar Cells by Full Glass Encapsulation

Dye-sensitized solar cells (DSSCs) emerged in the market as one of the most promising indoor photovoltaic technologies to address the need for wireless powering of low-consuming electronics and sensor nodes of the internet of things (IoT). The monolithic design structure of the cell (M-DSSCs) makes the devices simpler and cheaper, and it is straightforward for constructing in-series modules. The most efficient DSSCs reported so far are Co(III/II)-mediated liquid junction cells with acetonitrile electrolytes; however, they are mostly unstable. This study reports on highly stable cobalt-mediated M-DSSCs, passing thermal cycling tests up to 85 °C according to ISOS standard protocols. Under 1000 h of aging in the dark and under simulated solar and artificial light soaking, all tested cells improved or retained their initial power conversion efficiency. Advanced long-term stability was achieved by eliminating the extrinsic factors of degradation, such as the interaction of the cell components with the environment and electrolyte leakage. This was obtained by encapsulation of the devices using a glass-frit sealant, including the holes for filling up the liquid components of the cells. The hermeticity of the encapsulation complies with the MIL-STD-883 standard fine helium gas leakage test, and its hermeticity remained unchanged after humidity-freeze cycles according to IEC 61646. The elimination of extrinsic degradation factors allowed reliable assessment of inner factors accountable for aging. The impact of the ISOS-protocol test conditions on the intrinsic device stability and long-term photovoltaic history of the M-DSSCs is discussed.

α-Fe2O3/Reduced Graphene Oxide Composites as Cost-Effective Counter Electrode for Dye-Sensitized Solar Cells

The counter electrode (CE) is an important and vital part of dye-sensitized solar cells (DSSCs). Pt CEs show high-performance in DSSCs using iodide-based electrolytes. However, the high cost of Pt CEs restricts their large-scale application in DSSCs and the development of Pt-free CE is expected. Here, α-Fe2O3/reduced graphene oxide (α-Fe2O3/RGO) composites are prepared as the Pt-free CE materials for DSSCs. A simple hydrothermal technique was used to disseminate the α-Fe2O3 solid nanoparticles uniformly throughout the RGO surface. The presence of the α-Fe2O3 nanoparticles increases the specific surface area of RGO and allows the composites to be porous, which improves the diffusion of liquid electrolyte into the CE material. Then, the electrocatalytic properties of CEs with α-Fe2O3/RGO, α-Fe2O3, RGO, and Pt materials are compared. The α-Fe2O3/RGO CE has a similar electrocatalytic performance to Pt CE, which is superior to those of the pure α-Fe2O3 and RGO CEs. After being fabricated as DSSCs, the current–voltage measurements reveal that the DSSC based on α-Fe2O3/RGO CE has a power conversion efficiency (PCE) of 6.12%, which is 88% that of Pt CE and much higher than that of pure α-Fe2O3 and pure RGO CEs. All the results show that this work describes a promising material for cost-effective, Pt-free CEs for DSSCs.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Strong metal-support interactions enable highly transparent Pt-Mo2C counter electrodes of bifacial dye-sensitized solar cells

Highly transparent and active Pt-Mo₂C counter electrodes were successfully fabricated by the strong metal-support interaction, with high dispersity of Pt nanoclusters on Mo₂C support, which endowed bifacial dye-sensitized solar cells with a rear-to-front efficiency ratio as high as 0.75.

Transparent MoS2/PEDOT Composite Counter Electrodes for Bifacial Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are solar energy conversion devices with high efficiency and simple fabrication procedures. Developing transparent counter electrode (CE) materials for bifacial DSSCs can address the needs of window-type building-integrated photovoltaics (BIPVs). Herein, transparent organic-inorganic hybrid composite films of molybdenum disulfide and poly(3,4-ethylenedioxythiophene) (MoS₂/PEDOT) are prepared to take full advantage of the conductivity and electrocatalytic ability of the two components. MoS₂ is synthesized by hydrothermal method and spin-coated to form the MoS₂ layer, and then PEDOT films are electrochemically polymerized on top of the MoS₂ film to form the composite CEs. The DSSC with the optimized MoS₂/PEDOT composite CE shows power conversion efficiency (PCE) of 7% under front illumination and 4.82% under back illumination. Compared with the DSSC made by the PEDOT CE and the Pt CE, the DSSC fabricated by the MoS₂/PEDOT composite CE improves the PCE by 10.6% and 6.4% for front illumination, respectively. It proves that the transparent MoS₂/PEDOT CE owes superior conductivity and catalytic properties, and it is an excellent candidate for bifacial DSSC in the application of BIPVs.

Transparent Platinum Counter Electrode Prepared by Polyol Reduction for Bifacial, Dye-Sensitized Solar Cells

Pt catalytic nanoparticles on F-doped SnO₂/glass substrates were prepared by polyol reduction below 200 °C. The polyol reduction resulted in better transparency of the counter electrode and high power-conversion efficiency (PCE) of the resultant dye-sensitized solar cells (DSSCs) compared to conventional thermal reduction. The PCEs of the DSSCs with 5 μm-thick TiO₂ photoanodes were 6.55% and 5.01% under front and back illumination conditions, respectively. The back/front efficiency ratio is very promising for efficient bifacial DSSCs.

In situ preparation of Ru-N-doped template-free mesoporous carbons as a transparent counter electrode for bifacial dye-sensitized solar cells

The development of a highly active, long-lasting, and cost-effective electrocatalyst as an alternative to platinum (Pt) is a vital issue for the commercialization of dye-sensitized solar cells. In this study, Ru-N-doped template-free mesoporous carbon (Ru-N-TMC) was prepared by the direct stabilization and carbonization of the poly(butyl acrylate)-b-polyacrylonitrile (PBA-b-PAN) block copolymer and ruthenium(iii) acetylacetonate [Ru(acac)3]. During the stabilization process, microphase separation occurred in the PBA-b-PAN block copolymer due to the incompatibility between the two blocks, and the PAN block transformed to N-doped semi-graphitic carbon. In the carbonization step, the PBA block was eliminated as a porous template, creating hierarchal mesopores/micropores. Meanwhile, Ru(acac)3 was decomposed to Ru, which was homogeneously distributed over the carbon substrate and anchored through N and O heteroatoms. The resulting Ru-N-TMC showed ultra-low charge transfer resistance (Rct = 0.034 Ω cm2) in the Co(bipyridine)33+/2+ reduction reaction, indicating very high electrocatalytic ability. Even though it is a transparent counter electrode (CE, average visible transmittance of 42.25%), covering a small fraction of the fluorine doped tin oxide (FTO)/glass substrate with Ru-N-TMC, it led to lower charge transfer resistance (Rct = 0.55 Ω cm2) compared to Pt (Rct = 1.00 Ω cm2). The Ru-N-TMC counter electrode exhibited a superior power conversion efficiency (PCE) of 11.42% compared to Pt (11.16%) when employed in SGT-021/Co(bpy)33+/2+ based dye-sensitized solar cells (DSSCs). Furthermore, a remarkable PCE of 10.13% and 8.64% from front and rear illumination, respectively, was obtained when the Ru-N-TMC counter electrode was employed in a bifacial DSSC. The outstanding catalytic activity and PCE of Ru-N-TMC were due to the high surface area of Ru-N-TMC, which contained numerous active species (Ru and N), easily facilitated to redox ions through the hierarchical microporous/mesoporous structure.

Tellurium-Doped, Mesoporous Carbon Nanomaterials as Transparent Metal-Free Counter Electrodes for High-Performance Bifacial Dye-Sensitized Solar Cells

Tellurium-doped, mesoporous carbon nanomaterials with a relatively high doping level were prepared by a simple stabilization and carbonization method in the presence of a tellurium metalloid. A transparent counter electrode (CE) was prepared using tellurium-doped, mesoporous carbon (TeMC) materials, and was directly applied to bifacial, dye-sensitized solar cells (DSSCs). To improve the performance of the bifacial DSSC device, CEs should have outstanding electrocatalytic activity, electrical conductivity, and electrochemical stability, as well as high transparency. In this study, to make transparent electrodes with outstanding electrocatalytic activity and electrical conductivity, various TeMC materials with different carbonization temperatures were prepared by simple pyrolysis of the polyacrylonitrile-block-poly (n-butyl acrylate) (PAN-b-PBA) block copolymer in the presence of the tellurium metalloid. The electrocatalytic activity of the prepared TeMC materials were evaluated through a dummy cell test, and the material with the best catalytic ability was selected and optimized for application in bifacial DSSC devices by controlling the film thickness of the CE. As a result, the bifacial DSSC devices with the TeMC CE exhibited high power conversion efficiencies (PCE), i.e., 9.43% and 8.06% under front and rear side irradiation, respectively, which are the highest values reported for bifacial DSSCs to date. Based on these results, newly-developed transparent, carbon-based electrodes may lead to more stable and effective bifacial DSSC development without sacrificing the photovoltaic performance of the DSSC device.

High-Efficiency Bifacial Dye-Sensitized Solar Cells for Application under Indoor Light Conditions

High-efficiency, stable bifacial dye-sensitized solar cells (DSSCs) are prepared for application under indoor light conditions. A 3-methoxypropionitrile solvent and cobalt redox couples are utilized to prepare the electrolytes. To obtain the best cell performance, the components of the DSSCs, including electrolytes, photoanodes, and counter electrodes (CEs), are regulated. The experimental results indicate that an electrolyte comprising a Co (II/III) ratio of 0.11/0.025 M, 1.2 M 4-tert-butylpyridine, Y123 dye, a CE with the platinum (Pt) layer thickness of 0.16 nm, and a photoanode with titanium dioxide (TiO₂) layer thickness of 10 μm (6 μm main layer and 4 μm scattering layer) are the best conditions under which to achieve a high power conversion efficiency. It is also found that the best cells have high recombination resistance at the photoelectrode/electrolyte interface and low charge transfer resistance at the counter electrode/electrolyte interface, which contributes to, respectively, the high current density and open-circuit voltage of the corresponding cells. This DSSC can achieve efficiencies of 22.66%, 23.48%, and 24.52%, respectively, under T5 light illumination of 201.8, 607.8, and 999.6 lx. For fabrication of bifacial DSSCs with a semitransparent property, photoanodes without the TiO₂ scattering layer, as well as an ultrathin Pt film, are utilized. The thicknesses of the TiO₂ main layer and Pt film are reregulated. This shows that a Pt film with 0.55 nm thickness has both high transmittance (76.01%) and catalytic activity. By using an 8 μm TiO₂ main layer, optimal cell efficiencies of 20.65% and 17.31% can be achieved, respectively, for the front-side and back-side illuminations of 200 lx T5 light. The cells are highly stable during a long-term performance test at both 35 and 50 °C.

Recent Progress in the Design and Synthesis of Nitrides for Mesoscopic and Perovskite Solar Cells

With growing concerns about global warming and the energy crisis, a variety of photovoltaic devices have attracted worldwide attention as alternative energy sources. Among them, organic-inorganic hybrid photovoltaics, typically mesoscopic and perovskite solar cells, are promising, owing to their potential for low-cost energy production, which mainly comes from unlimited combinations of materials optimized for each step of solar energy conversion. However, the commercialization of organic-inorganic hybrid solar cells is hampered by costly electrocatalysts or hole-transport materials. Currently, state-of-the-art dye- or quantum-dot-sensitized solar cells and perovskite solar cells necessitate noble metals and high-price polymeric materials. In an attempt to resolve this issue, various kinds of metal compounds have been investigated, and nitrides have been actively reported to possess a number of favorable properties for the aforementioned purpose, such as excellent electrical conductivity and superb electrocatalytic performance. Herein, the use of nitrides as cost-effective electrocatalysts or hole-transport materials in organic-inorganic hybrid solar cells is reviewed. Nitrides with a variety of morphologies and scales are discussed, together with the synergistic effect in the case of diverse composites. In addition, prospects and challenges for applying nitride materials are briefly suggested.

Bifunctional Photo-Supercapacitor with a New Architecture Converts and Stores Solar Energy as Charge

Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO₂ is used as the solar cell. Poly(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO₂) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO₂ coatings, which serve as the CEs for the TiO₂/hb/CdS photoanode and yet another PEDOP@MnO₂ electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm^-2) illumination, the TiO₂/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO₂ electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g^-1, an energy density of 13.2 Wh kg^-1, and a power density of 360 W kg^-1 at a discharge current density of 1 A g^-1. During the self-discharge process, PEDOP@MnO₂-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO₂/hb/CdS photoanode with the PEDOP@MnO₂ CE in an aqueous polysulfide-silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.