Research of CH3NH3PbI3 perovskite solar cells had significant attention as the candidate of new future energy. Due to the toxicity, however, lead (Pb) free photon harvesting layer should be discovered to replace the present CH3NH3PbI3 perovskite. In place of lead, we have tried antimony (Sb) and bismuth (Bi) with organic and metal monovalent cations (CH3NH3 +, Ag+ and Cu+). Therefore, in this work, lead-free photo-absorber layers of (CH3NH3)3Bi2I9, (CH3NH3)3Sb2I9, (CH3NH3)3SbBiI9, Ag3BiI6, Ag3BiI3(SCN)3 and Cu3BiI6 were processed by solution deposition way to be solar cells. About the structure of solar cells, we have compared the normal (n-i-p: TiO2-perovskite-spiro OMeTAD) and inverted (p-i-n: NiO-perovskite-PCBM) structures. The normal (n-i-p)-structured solar cells performed better conversion efficiencies, basically. But, these environmental friendly photon absorber layers showed the uneven surface morphology with a particular grow pattern depend on the substrate (TiO2 or NiO). We have considered that the unevenness of surface morphology can deteriorate the photovoltaic performance and can hinder future prospect of these lead-free photon harvesting layers. However, we found new interesting finding about the progress of devices by the interface of NiO/Sb3+ and TiO2/Cu3BiI6, which should be addressed in the future study.

Inexpensive and sensitive graphite electrodes were fabricated by applying flame annealing to pencil-graphite rods (PGRs) as electrodes for water electrolysis cells. The resin (polymer, binder) on the surface of PGR was removed by flame annealing to make it porous, and the graphite electrodes with high activity and low cost were obtained. By flame annealing the PGR, although the PGR electrode became active upon water electrolysis, the PGR electrode became instable for long-time operation. The effects of flame annealing on PGR for water electrolysis were analyzed by SEM, FT-IR spectroscopy, Raman spectroscopy, NEXAFS, and electrochemical impedance spectroscopy (EIS).

Organic‐inorganic CH3NH3PbI3‐based perovskite solar cells have received significant research interest; however, thermal stability issue still remains. Carbon‐based triple‐porous‐layer perovskite solar cells without any hole transporting material were selected in order to investigate the internal degradation process by thermal stresses. The sealed perovskite solar cells at 100 °C showed stable performance in the power conversion efficiency up to 4500 h, but the degradation was accelerated after that. By analyzing the perovskite solar cells aged for 7000 h at 100 °C, the results of energy dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy suggest that, although Pb, I, and N were sealed inside of the devices, a plenty amount of CH3NH3+ deactivated in the sealant UV‐curable adhesive at 100 °C, which is the reason of the thermal degradation for the sealed perovskite solar cells.

An inexpensive, simple, and high-activity catalyst preparation method has been introduced in this work. Pt and RuO x catalysts were fabricated by soaking inexpensive graphite electrodes (pencil-lead graphite rod: PGR) in catalyst precursor solutions and using a simple flame-annealing method, which results in lower amount of Pt and RuO x catalyst layers. From X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure analysis, it has been found that platinum and ruthenium were deposited as zero-valence metal (Pt) and oxide (RuO x ), respectively. Catalytic activities of Pt/PGR and RuO x /PGR for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were evaluated using neutral 1 M Na 2 SO 4 aqueous electrolyte, respectively. Although HER and OER currents using PGR without catalysts were −16 mA cm −2 (at −1.5 V vs Ag/AgCl) and +20 mA cm −2 (at +2.0 V vs Ag/AgCl), they were improved to −110 and +80 mA cm −2 with catalysts (Pt and RuO x ), respectively. Such an inexpensive and rapid catalyst electrode preparation method on PGR using flame-annealing is a very significant method in the initial catalyst activity evaluation requiring a large amount of trial and error.

Society is demanding clean energy to substitute the greatly pollutant carbon-based fuels. As an alternative, the green hydrogen produced by electrocatalysis constitutes a nice strategy as its products and reactants...