Solid Electrolyte Interphase Formation in Tellurium Iodide Perovskites during Electrochemistry and Photoelectrochemistry

Halide perovskites are promising photoelectrocatalytic materials. Their further development requires understanding of surface processes during electrochemistry. Thin films of tellurium-based vacancy-ordered perovskites with formula A₂TeI₆, A = Cs, methylammonium (MA), were deposited onto transparent conducting substrates using aerosol-assisted chemical vapor deposition. Thin film stability as electrodes and photoelectrodes was tested in dichloromethane containing tetrabutylammonium PF₆ (TBAPF₆). Using photoemission spectroscopy, we show that the formation of a solid electrolyte interphase on the surface of the Cs₂TeI₆, consisting of CsPF₆, enhances the stability of the electrode and allows extended chopped-light chronoamperometry measurements at up to 1.1 V with a photocurrent density of 16 μA/cm². In contrast, (CH₃NH₃)₂TeI₆ does not form a passivating layer and rapidly degrades upon identical electrochemical treatment. This demonstrates the importance of surface chemistry in halide perovskite electrochemistry and photoelectrocatalysis.

Scalable Production of Ambient Stable Hybrid Bismuth-Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films*

Large homogeneous and adherent coatings of phenethylammonium bismuth iodide were produced using the cost-effective and scalable aerosol-assisted chemical vapor deposition (AACVD) methodology. The film morphology was found to depend on the deposition conditions and substrates, resulting in different optical properties to those reported from their spin-coated counterparts. Optoelectronic characterization revealed band bending effects occurring between the hybrid material and semiconducting substrates (TiO2 and FTO) due to heterojunction formation, and the optical bandgap of the hybrid material was calculated from UV-visible and PL spectrometry to be 2.05 eV. Maximum values for hydrophobicity and crystallographic preferential orientation were observed for films deposited on FTO/glass substrates, closely followed by values from films deposited on TiO2 /glass substrates.

Thin films of formamidinium lead iodide (FAPI) deposited using aerosol assisted chemical vapour deposition (AACVD)

Formamidinium lead iodide (CH(NH₂)₂PbI₃, FAPI) thin films have been deposited on glass substrates at 150 °C using ambient pressure aerosol assisted chemical vapour deposition (AACVD). The films have been analysed by a range of techniques including powder X-ray diffraction (pXRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and UV–Vis–NIR absorption spectroscopy. Sharp reflections in the pXRD pattern can be indexed to the α-phase of FAPI which confirms the crystallinity of the as-deposited film and reveals a preferred growth orientation along the (002) plane with respect to the substrate. High magnification SEM images show that the thin film is comprised of a network of intimately connected FAPI crystallites which form a mesoporous architecture. EDX mapping of lead and iodine emission peaks show that the Pb and I within these films are spatially co-localised. Optical measurements show as-deposited FAPI films have absorption onsets in the near infra-red with a direct bandgap value of 1.46 eV, suitable for single junction solar cells. Four-point probe measurement of as deposited films show that the electrical conductivity (σ) of the FAPI thin film is 5.2 × 10^–7 S/cm, which is similar to FAPI thin films deposited by spin coating technique.

Unusual Thermal Boundary Resistance in Halide Perovskites: A Way To Tune Ultralow Thermal Conductivity for Thermoelectrics

Halide perovskites have emerged as promising candidates as the active material in photovoltaics and light-emitting diodes. They possess unusual bulk thermal transport properties that have been the focus of a number of studies, but there is much less understanding of thermal transport in thin films where a diverse range of structures and morphologies are accessible. Here, we report on the tuning of in-plane thermal conductivity in methylammonium lead iodide thin films by morphological control. Using 3-ω measurements, we find that the room temperature thermal conductivity of thermally evaporated methylammonium lead iodide perovskite films ranges from 0.31 to 0.59 W/(m K). We measure a discontinuity in thermal conductivity at the orthorhombic-tetragonal phase transition and explore this using density functional theory and attributing it to a collapse in the phonon group velocity along the c-axis of the tetragonal crystal. Moreover, we have quantified the thermal boundary resistance (Kapitza resistance) for thermally evaporated films, allowing us to estimate the Kapitza length, which is 36 ± 2 nm at room temperature and 15 ± 2 nm at 100 K. Curiously, the Kapitza resistance has a strong temperature dependence which we also explore using density functional theory, with these results suggesting an important role of methylammonium rotational modes in scattering phonons at the crystallite boundaries.

A Review of Perovskite Photovoltaic Materials' Synthesis and Applications via Chemical Vapor Deposition Method

Perovskite photovoltaic materials (PPMs) have emerged as one of superstar object for applications in photovoltaics due to their excellent properties-such as band-gap tunability, high carrier mobility, high optical gain, astrong nonlinear response-as well as simplicity of their integration with other types of optical and electronic structures. Meanwhile, PPMS and their constructed devices still present many challenges, such as stability, repeatability, and large area fabrication methods and so on. The key issue is: how can PPMs be prepared using an effective way which most of the readers care about. Chemical vapor deposition (CVD) technology with high efficiency, controllability, and repeatability has been regarded as a cost-effective road for fabricating high quality perovskites. This paper provides an overview of the recent progress in the synthesis and application of various PPMs via the CVD method. We mainly summarize the influence of different CVD technologies and important experimental parameters (temperature, pressure, growth environment, etc.) on the stabilization, structural design, and performance optimization of PPMS and devices. Furthermore, current challenges in the synthesis and application of PPMS using the CVD method are highlighted with suggested areas for future research.

Organo-Lead Halide Perovskite Induced Electroactive β-Phase in Porous PVDF Films: An Excellent Material for Photoactive Piezoelectric Energy Harvester and Photodetector

Methylammonium lead iodide (CH₃NH₃PbI₃) (MAPI)-embedded β-phase comprising porous poly(vinylidene fluoride) (PVDF) composite (MPC) films turns to an excellent material for energy harvester and photodetector (PD). MAPI enables to nucleate up to ∼91% of electroactive phase in PVDF to make it suitable for piezoelectric-based mechanical energy harvesters (PEHs), sensors, and actuators. The piezoelectric energy generation from PEH made with MPC film has been demonstrated under a simple human finger touch motion. In addition, the feasibility of photosensitive properties of MPC films are manifested under the illumination of nonmonochromatic light, which also promises the application as organic photodetectors. Furthermore, fast rising time and instant increase in the current under light illumination have been observed in an MPC-based photodetector (PD), which indicates of its potential utility in efficient photoactive device. Owing to the photoresponsive and electroactive nature of MPC films, a new class of stand-alone self-powered flexible photoactive piezoelectric energy harvester (PPEH) has been fabricated. The simultaneous mechanical energy-harvesting and visible light detection capability of the PPEH is promising in piezo-phototronics technology.

Compact Layers of Hybrid Halide Perovskites Fabricated via the Aerosol Deposition Process-Uncoupling Material Synthesis and Layer Formation

We present the successful fabrication of CH₃NH₃PbI₃ perovskite layers by the aerosol deposition method (ADM). The layers show high structural purity and compactness, thus making them suitable for application in perovskite-based optoelectronic devices. By using the aerosol deposition method we are able to decouple material synthesis from layer processing. Our results therefore allow for enhanced and easy control over the fabrication of perovskite-based devices, further paving the way for their commercialization.

Sequential bottom-up and top-down processing for the synthesis of transition metal dichalcogenide nanosheets: the case of rhenium disulfide (ReS2)

Bottom-up (aerosol-assisted chemical vapor deposition, AACVD) and top-down (liquid phase exfoliation, LPE) processing methodologies are used in tandem to produce colloids of few-layer thick rhenium disulfide (ReS₂) in N-methyl pyrrolidone.