Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO2 Photoelectrodes and Pyrazine-Based Photosensitizers.

In this study, to obtain high performances of the dye-sensitized solar cells using the optimal TiO2 photoelectrode for the synthesized pyrazine-based organic photosensitizers, three types of TiO2 photoelectrodes were fabricated and evaluated for comparison. The double-layered nanoporous TiO2 photoelectrode (SPD type) consisted of a dispersed TiO2 layer and a transparent TiO2 layer. The single-layered nanoporous TiO2 photoelectrodes (D type and SP type) consisted of a dispersed TiO2 layer and a transparent TiO2 layer, respectively. The surface area, pore volume, and crystalline structures of the three types of TiO2 photoelectrodes were analyzed by Brunauer-Emmett-Teller method, field-emission scanning electron microscopy, and X-ray diffractometry to confirm their crystallinity and surface morphology. The structures of the three types of TiO2 photoelectrode-adsorbed organic sensitizers were investigated using X-ray photoelectron spectroscopy. The photovoltaic performances of DSSC devices using three organic photosensitizers adsorbed onto the three types of TiO2 photoelectrodes were investigated under a light intensity of 100 mW/cm2 at AM 1.5. The DSSC device using double-layered SPD type TiO2 photoelectrodes displayed 1.31∼2.64% efficiency, compared to single-layered SP type TiO2 photoelectrodes (1.31∼2.50%) and D type TiO2 photoelectrodes (0.90∼1.54%), using organic photosensitizers. The DSSC device using the SPD type TiO2 photoelectrode and trifluoromethylbenzopyrazine (TPPF) as a photosensitizer showed the highest performances: J sc of 5.69 mA/cm2, V oc of 0.69 V, FF of 0.67, and efficiency of 2.64%. The relationship between photovoltaic effects and interfacial resistance characteristics of DSSCs using the three organic photosensitizers adsorbed onto the three types of TiO2 photoelectrodes could be interpreted from interfacial resistances according to frequency through impedance analysis.

Tailoring the Interface with a Multifunctional Ligand for Highly Efficient and Stable FAPbI3 Perovskite Solar Cells and Modules.

Perovskite solar cells (PeSCs) using FAPbI3 perovskite films often exhibit unfavorable phase transitions and defect-induced nonradiative interfacial recombination, resulting in considerable energy loss and impairing the performance of PeSCs in terms of efficiency, stability, and hysteresis. In this work, a facile interface engineering strategy to control the surface structure and energy-level alignment of perovskite films by tailoring the interface between the FAPbI3 film and hole-transporting layer using 4-hydroxypicolinic acid (4HPA) is reported. According to density functional theory studies, 4HPA has prominent electron delocalization distribution properties that enable it to anchor to the perovskite film surface and facilitate charge transfer at the interface. By enabling multiple bonding interactions with the perovskite layer, including hydrogen bonds, PbO, and PbN dative bonds, 4HPA passivation significantly reduces the trap density and efficiently suppresses nonradiative recombination. The obtained perovskite films exhibit superior optoelectronic properties with improved crystallinity, pure α-phase FAPbI3 , and favorable energy band bending. Following this strategy, 4HPA post-treatment PeSCs achieve a champion power conversion efficiency of 23.28% in 0.12 cm2 cells and 19.26% in 36 cm2 modules with excellent environmental and thermal stabilities.

Photovoltaic Performances of Dye-Sensitized Solar Cells Based on Modified Polybutadiene Matrix Electrolytes by Sol-Gel Process.

A new type of polymer matrix electrolyte based on modified polybutadiene (modified PB) was developed for dye-sensitized solar cells (DSSCs) to improve their stability. The modified PB was fabricated by cross-linking the reaction of polybutadiene with siloxane groups as a substitute sol-gel process. A DSSC device using the modified PB matrix electrolyte showed an open-circuit voltage of 0.64 V, a short-circuit current density of 15.00 mA/cm2, and a fill factor of 0.58 under photointensity of 100 mW/cm2 at AM 1.5, consequently leading to an overall solar energy conversion efficiency of 5.49%. The DSSC device using the modified PB matrix electrolyte improved the conductivity, and the charge transfer ability showed the outstanding stability of the device.

Water-Repellent Perovskites Induced by a Blend of Organic Halide Salts for Efficient and Stable Solar Cells.

Despite tremendous progress in the power conversion efficiency (PCE) of perovskite solar cells (PeSCs), the long-term stability issue remains a significant challenge for commercialization. In this study, by blending organic halide salts, phenylethylammonium halide (PEAX, X = I, Br), with CH3NH3PbI3 (MAPbI3), we achieved remarkable enhancements in the water-repellency of perovskite films and long-term stability of PeSCs, together with enhanced PCE. The hydrophobic aromatic PEA+ group in PEAX protects the perovskite film from destruction by water. In addition, the smaller halide Br- in PEABr restructures MAPbI3 to form MAPbI3-xBrx during post-annealing, leading to lattice contraction with beneficial crystallization quality. The perovskite films modified by PEAX exhibited excellent water resistance. When the perovskite films were directly immersed in water, no obvious decompositions were observed, even after 60 s. The PEAX-decorated PeSCs exhibited considerable long-term stability. Under high-humidity conditions (60 ± 5%), the PEAX-decorated PeSCs held 80.5% for PEAI and 85.2% for PEABr of their original PCE after exposure for 100 h, whereas the pristine PeSC device lost more than 99% of its initial PCE after exposure for 60 h under the same conditions. Moreover, compared to the pristine device with a PCE of 13.28%, the PEAX-decorated PeSCs exhibited enhanced PCEs of 17.33% for the PEAI device and 17.18% for the PEABr device.

Kerf-Less Exfoliated Thin Silicon Wafer Prepared by Nickel Electrodeposition for Solar Cells.

Ultra-thin and large-area silicon wafers with a thickness in the range of 20-70 µm, were produced by spalling using a nickel stressor layer. A new equation for predicting the thickness of the spalled silicon was derived from the Suo-Hutchinson mechanical model and the kinking mechanism. To confirm the reliability of the new equation, the proportional factor of stress induced by the nickel on the silicon wafer, was calculated. The calculated proportional factor of λ = 0.99 indicates that the thickness of the spalled silicon wafer is proportional to that of the nickel layer. A similar relationship was observed in the experimental data obtained in this study. In addition, the thickness of the stressor layer was converted to a value of stress as a guide when using other deposition conditions and materials. A silicon wafer with a predicted thickness of 50 µm was exfoliated for further analysis. In order to spall a large-area (150 × 150 mm2 or 6 × 6 in2) silicon wafer without kerf loss, initial cracks were formed by a laser pretreatment at a proper depth (50 µm) inside the exfoliated silicon wafer, which reduced the area of edge slope (kerf loss) from 33 to 3 mm2. The variations in thickness of the spalled wafer remained under 4%. Moreover, we checked the probability of degradation of the spalled wafers by using them to fabricate solar cells; the efficiency and ideality factor of the spalled silicon wafers were found to be 14.23%and 1.35, respectively.