CoO is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoO/CHNHPbI/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.5 G 1 sun irradiation, which is significantly superior to those of materials fabricated with a traditional HEL such as PEDOT:PSS (12.2%), NiO (10.2%), and CuO (9.4%) under the same experimental conditions. We characterized the chemical compositions with XPS, crystal structures with XRD, and film morphology with SEM/AFM techniques. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite deposited on varied HEL films were recorded to obtain the hole-extracting characteristics, for which the hole-extracting times show the order CoO (2.8 ns) < PEDOT:PSS (17.5 ns) < NiO (22.8 ns) < CuO (208.5 ns), consistent with the trend of their photovoltaic performances. The reproducibility and enduring stability of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoO device retained PCE ≈ 12% for over 1000 h.

Optimization of a compact layer of TiO 2 via atomic-layer deposition for high-performance perovskite solar cells A uniform and pinhole-free compact layer of TiO 2 was produced via atomic-layer deposition for mesoporous perovskite solar cells with a n-i-p confi guration. The best power conversion effi ciency of the cell attained 15.0% with a minor hysteresis eff ect. The devices showed great stability and reproducibility, providing an alternative for high-performance perovskite solar cells. As featured in:See We report the effect of thickness of a film consisting of a compact layer of TiO 2 produced via atomic-layer deposition (ALD) for mesoporous perovskite solar cells (PSCs) with a n-i-p configuration. Uniform and pinhole-free TiO 2 films of thickness from 10 to 400 nm were deposited on fluorine-doped tin-oxide substrates using ALD. The device performance of the PSC showed a trend systematic with the thickness of the ALD-TiO 2 compact layer and attained the best efficiency, 15.0%, of power conversion at thickness 200 nm. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite (PSK) deposited on varied ALD-TiO 2 films were recorded; the effective PL quenching is due to electron transfer from PSK into the ALD-TiO 2 compact layer. The most efficient interfacial electron transfer occurred at film thickness 200 nm, for which the ALD-TiO 2 film has the greatest surface roughness and conductivity. We found a systematic correlation between the device performance in relation to the conductivity and the rate of interfacial electron transfer as a function of thickness of the ALD-TiO 2 film; the best performance occurred at thickness 200 nm. The devices showed great stability and reproducibility, providing an alternative for high-performance PSCs with a well-controlled TiO 2 compact layer.

Schiff bases represent an essential class in organic chemistry with antitumor, antiviral, antifungal, and antibacterial activities. The synthesis of Schiff bases requires the presence of an organic base as a catalyst such as piperidine. Base-free synthesis of organic compounds using a heterogeneous catalyst has recently attracted more interest due to the facile procedure, high yield, and reusability of the used catalyst. Herein, we present a comparative study to synthesize new Schiff bases containing indole moieties using piperidine as an organic base catalyst and Au@TiO 2 as a heterogeneous catalyst. In both methods, the products were isolated in high yields and fully characterized using different spectral analysis techniques. The catalyst was reusable four times, and the activity was slightly decreased. The presence of Au increases the number of acidic sites of TiO 2 , resulting in C=O polarization. Yields of the prepared Schiff bases in the presence of Au@TiO 2 and piperidine were comparable. However, Au@TiO 2 is an easily separable and recyclable catalyst, which would facilitate the synthesis of organic compounds without applying any hazardous materials. Furthermore, the luminescence behavior of the synthesized Schiff bases exhibited spectral shape dependence on the substituent group. Interestingly, the compounds also displayed deep-blue fluorescence with Commission Internationale de l’Éclairage (CIE) coordinates of y < 0.1. Thus, these materials may contribute to decreasing the energy consumption of the emitting devices.

Lead halide based perovskite semiconductors self-assemble with distinct organic cations in natural multi-quantum-well structures. The emerging electronic properties of these two-dimensional (2D) materials can be controlled by the combination of...

Mixed-cation perovskites exhibit outstanding performance as next-generation solar cells and for optoelectronic applications. One pathway to increase the quality and stability of these materials is adding Cs to the Asite of mixed-cation formamidinium/methylammonium in the perovskite APbX 3 . Here, we use femtosecond transient absorption spectroscopy to study the effect of Cs on the dynamics of a mixed-cation wide band gap bromidebased perovskite. Negligible changes in the optical spectra are observed between the two films, indicating a similar localization of the charge carriers at the band edge. However, adding Cs reduces the non-radiative recombination sites and increases the lifetime of the photogenerated charge carriers in the perovskite film (from 291 to 355 ns). Furthermore, the Cs cation slows down the cooling of hot carriers through an efficient hot-phonon bottleneck, which is observed by increasing the excitation power from 9.7 to 648 μJ/cm 2 [the lifetime of the fast component (τ 1 ) increases from 0.21 to 0.91 ps]. Understanding the mechanism of charge dynamics in perovskite thin films is critical for the fabrication of high-performance devices.