Stability of MAPbI3 perovskite grown on planar and mesoporous electron-selective contact by inverse temperature crystallization.

Single crystalline perovskite solar cells (PSC) are promising for their inherent stability due to the absence of grain boundaries. While the development of single crystals of perovskite with enhanced optoelectronic properties is known, studies on the growth, device performance and understanding of the intrinsic stability of single crystalline perovskite thin film solar cell devices fabricated on electron selective contacts are scarcely explored. In this work, we examine the impact of mesoporous TiO2 (m-TiO2) and planar TiO2 (p-TiO2) on the growth of single crystalline-methyl ammonium lead iodide (SC-MAPbI3) film, PSC device performance and film stability under harsh weather conditions (T ∼ 85 °C and RH ∼ 85%). Self-grown SC-MAPbI3 films are developed on m-TiO2 and p-TiO2 by inverse temperature crystallization under ambient conditions without the need for sophisticated glove-box processing. The best device with m-TiO2 as an electron transport layer showed a promising power conversion efficiency of 3.2% on an active area of 0.3 cm2 in hole transport material free configuration, whereas, only 0.7% was achieved for the films developed on p-TiO2. Complete conversion of precursor to perovskite phase and better surface coverage of the film leading to enhanced absorption and reduced defects of single crystalline perovskite on m-TiO2 compared to its p-TiO2 leads to this large difference in efficiency. Mesoporous device retained more than 70% of its initial performance when stored at 30 °C under dark for more than 5000 h at 50% RH; while the planar device degraded after 1500 h. Thermal and moisture endurance of SC-MAPbI3 films are investigated by subjecting them to temperatures ranging from 35 °C to 85 °C at a constant relative humidity (RH) of 85%. X-ray diffraction studies show that the SC-MAPbI3 films are stable even at 85 °C and 85% RH, with only slight detection (30-35%) of PbI2 at these conditions. This study highlights the superior stability of SC-MAPbI3 films which paves way for further studies on improving the stability and performance of the ambient processed PSCs.

Prickly pear fruit extract as photosensitizer for dye-sensitized solar cell.

In this study, we have explored prickly pear fruit extract as a photosensitizer in dye-sensitized solar cells (DSSC). The photosensitizer was isolated from prickly pear fruits by extraction method using ethanol as solvent. Structural, morphological and optical properties of prickly pear extract characterized by XRD, SEM, UV-VIS-DRS, FTIR spectra, respectively. UV-VIS absorption and FTIR spectra of prickly pear fruit extract confirm the presence of betacyanin and hydroxyl groups anchoring onto the TiO2 surface. The absorption maxima at 534 nm in the visible region is prominent. The presence of betacyanin in the extract is indicative that the dye will be useful as a sensitizer in DSSC. Reflectance edge of TiO2 is red-shifted upon the adsorption of natural dye. The XPS analysis showed the charge state of hydroxyl (O-H) groups that are attached with the natural dye adsorbed onto the surface of TiO2. The fabricated DSSC had a conversion efficiency (ɳ) of 0.56% with highest fill factor (FF) of 0.85, open-circuit voltage (Voc) of 0.56 V and short circuit-current density (Jsc) with 1.17 mA/cm2. The value obtained for the fill factor is promising to further explore the prickly pear extract for applicability in DSSC by improving the efficiency.

Preparation of gold nanoparticles using Salicornia brachiata plant extract and evaluation of catalytic and antibacterial activity.

The current study deals with the synthesis of gold nanoparticles (AuNPs) using Salicornia brachiata (Sb) and evaluation of their antibacterial and catalytic activity. The SbAuNPs showed purple color with a characteristic surface plasmon resonance peak at 532 nm. Scanning electron microscopy and transmission electron microscopy revealed polydispersed AuNPs with the size range from 22 to 35 nm. Energy dispersive X-ray and thin layer X-ray diffraction analysis clearly shows that SbAuNPs was pure and crystalline in nature. As prepared gold nanoparticles was used as a catalyst for the sodium borohydride reduction of 4-nitro phenol to 4-amino phenol and methylene blue to leucomethylene blue. The green synthesized nanoparticles exhibited potent antibacterial activity against the pathogenic bacteria, as evidenced by their zone of inhibition. In addition, we showed that the SbAuNPs in combination with the regular antibiotic, ofloxacin, exhibit superior antibacterial activity than the individual.

Multi-functionality of macroporous TiO2 spheres in dye-sensitized and hybrid heterojunction solar cells.

Micron-sized macroporous TiO2 spheres (MAC-TiO2) were synthesized using a colloidal templating process inside emulsions, which were then coated on a nanocrystalline TiO2 light absorption film to prepare a bilayered photoanode for liquid-based dye-sensitized solar cells (DSSC) and hybrid heterojunction solid-state solar cells. MAC-TiO2 layers can enhance light scattering as well as absorption, because their pore size and periodicity are comparable to light wavelength for unique multiple scattering and a porous surface can load dye more. Moreover, due to the bicontinuous nature of macropores and TiO2 walls, electrolyte could be transported much faster in between the TiO2 spheres rather than within the small TiO2 nonporous architectures. Electron transport was also facilitated along the interconnected TiO2 walls. In DSSCs with these MAC-TiO2 scattering layers, efficiency was higher than conventional DSSCs incorporating a commercial scattering layer. The unique geometry of MAC-TiO2 results in strong improvements in light scattering and infiltration of hole-transporting materials, thereby the MAC-TiO2-based solid-state device showed comparatively higher efficiency than the device with conventional nanocrystalline TiO2.

Sub-micrometer-sized graphite as a conducting and catalytic counter electrode for dye-sensitized solar cells.

Sub-micrometer-sized colloidal graphite (CG) was tested as a conducting electrode to replace transparent conducting oxide (TCO) electrodes and as a catalytic material to replace platinum (Pt) for I(3)(-) reduction in dye-sensitized solar cell (DSSC). CG paste was used to make a film via the doctor-blade process. The 9 µm thick CG film showed a lower resistivity (7 Ω/◻) than the widely used fluorine-doped tin oxide TCO (8-15 Ω/◻). The catalytic activity of this graphite film was measured and compared with the corresponding properties of Pt. Cyclic voltammetry and electrochemical impedance spectroscopy studies clearly showed a decrease in the charge transfer resistance with the increase in the thickness of the graphite layer from 3 to 9 µm. Under 1 sun illumination (100 mW cm(-2), AM 1.5), DSSCs with submicrometer-sized graphite as a catalyst on fluorine-doped tin oxide TCO showed an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt. DSSCs with a graphite counter electrode (CE) on TCO-free bare glass showed an energy conversion efficiency greater than 5.0%, which demonstrated that the graphite layer could be used both as a conducting layer and as a catalytic layer.