Impact of Humidity and Temperature on the Stability of the Optical Properties and Structure of MAPbI3, MA0.7FA0.3PbI3 and (FAPbI3)0.95(MAPbBr3)0.05 Perovskite Thin Films

Implications of Electron Transport Layer and Back Metal Contact Variations in Tin-Lead Perovskite Solar Cells Assessed by Spectroscopic Ellipsometry and External Quantum Efficiency

The structural and optical properties of hybrid organic-inorganic metal halide perovskite solar cells are measured by spectroscopic ellipsometry to reveal an optically distinct interfacial layer among the back contact metal, charge transport, and absorber layers. Understanding how this interfacial layer impacts performance is essential for developing higher performing solar cells. This interfacial layer is modeled by Bruggeman effective medium approximations (EMAs) to contain perovskite, C₆₀, BCP, and metal. External quantum efficiency (EQE) simulations that consider scattering, electronic losses, and the formation of nonparallel interfaces are created with input derived from ellipsometry structural-optical models and compared with experimental EQE to estimate optical losses. This nonplanar interface causes optical losses in short circuit current density (J_SC) of up to 1.2 mA cm^-2. A study of glass/C₆₀/SnO₂/Ag or Cu and glass/C₆₀/BCP/Ag film stacks shows that C₆₀ and BCP mix, but replacing BCP with SnO₂ can prevent mixing between the ETLs to prevent contact between C₆₀ and back contact metal and enable the formation of a planar interface between ETLs and back contact metals.

Influence of Sb3+ Cations on the Structural, Magnetic and Electrical Properties of AlFeO3 Multiferroic Perovskite with Humidity Sensors Applicative Characteristics

The effects of Sb³⁺ cations substitution on the structural, magnetic and electrical properties of Al_1-xSb_xFeO₃ multiferroic perovskite are investigated. The partial or total substitution of Al³⁺ cations with Sb³⁺ cations, in stoichiometric composition Al_1-xSb_xFeO₃ (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were made in order to identify composite materials with sensors applicative properties. Multiferroic perovskite samples were prepared following technology of the ceramic solid-state method, and the thermal treatments were performed in air atmosphere at 1100 °C temperature. The X-ray diffraction studies have confirmed the phase composition of samples and scanning electron microscopy the shape of the crystallites has been evidenced. The perovskite material was subjected to representative magnetic investigations in order to highlight substitutions characteristics. Investigations on electrical properties have evidenced the substitution dependence of relative permittivity and electrical resistivity under humidity influence and the characteristics of humidity sensors based on this material. The results are discussed in term of microstructural changes induced by the substitutions degree and its sensor applicative effects.

A Study to Improve the Performance of Mixed Cation-Halide Perovskite-Based UVC Photodetectors

Photodetectors convert optical signals into electrical signals and demonstrate application potential in various fields, such as optical communication, image detection, environmental monitoring, and optoelectronics. In this study, a mixed cation-halide perovskite-based ultraviolet C photodetector was fabricated using a solution process. The higher the mobility of the perovskite carrier, which is one of the factors affecting the performance of electronic power devices, the better the carrier diffusion. The on/off ratio and responsivity indicate the sensitivity of the response, and together with the detectivity and external quantum efficiency, these parameters demonstrate the performance of the detector. The detector fabricated in this study exhibited a mobility of 202.2 cm2/Vs and a high on/off ratio of 105% at a -2 V bias, under 254 nm light irradiation with an intensity of 0.6 mW/cm2. The responsivity, detectivity, and external quantum efficiency of the as-fabricated detector were 5.07 mA/W, 5.49 × 1011 Jones, and 24.8%, respectively. These findings demonstrate that the solution process employed in this study is suitable for the fabrication of mixed cation-halide perovskites which show immense potential for use as photodetectors.

Quantitative Predictions of Moisture-Driven Photoemission Dynamics in Metal Halide Perovskites via Machine Learning

Metal halide perovskite (MHP) photovoltaics may become a viable alternative to standard Si-based technologies, but the current lack of long-term stability precludes their commercial adoption. Exposure to standard operational stressors (light, temperature, bias, oxygen, and water) often instigate optical and electronic dynamics, calling for a systematic investigation into MHP photophysical processes and the development of quantitative models for their prediction. We resolve the moisture-driven light emission dynamics for both methylammonium lead tribromide and triiodide thin films as a function of relative humidity (rH). With the humidity and photoluminescence time series, we train recurrent neural networks and establish their ability to quantitatively predict the path of future light emission with 18% error over 4 h. Together, our in situ rH-PL measurements and machine learning forecasting models provide a framework for the rational design of future stable perovskite devices and, thus, a faster transition toward commercial applications.

Urbach Energy and Open-Circuit Voltage Deficit for Mixed Anion-Cation Perovskite Solar Cells

The Urbach energy indicating the width of the exponentially decaying sub-bandgap absorption tail is commonly used as the indicator of electronic quality of thin-film materials used as absorbers in solar cells. Urbach energies of hybrid inorganic-organic metal halide perovskites with various anion-cation compositions are measured by photothermal deflection spectroscopy. The variation in anion-cation composition has a substantial effect on the measured Urbach energy and hence the electronic quality of the perovskite. Depending upon the compositions, the Urbach energy varies from 18 to 65 meV for perovskite films with similar bandgap energies. For most of the perovskite compositions studied here including methylammonium (MA) + formamidinium (FA)-based Pb iodides, mixed Sn + Pb narrow-bandgap perovskites with low or intermediate Sn contents, and wide-bandgap FA + Cs- and I + Br-based perovskites, the correlation between the Urbach energy of the perovskite thin film and open-circuit voltage (V_OC) deficit for corresponding solar cells shows a direct relationship with reduction of the Urbach energy occurring with a beneficial decrease in the V_OC deficit. However, due to issues related to material quality, impurity phases and stability in laboratory ambient air, and unoptimized film processing techniques, the solar cells incorporating Cs-based inorganic and mixed Sn + Pb perovskites with a higher than optimum Sn content show a higher V_OC deficit even though the corresponding films show a lower Urbach energy.

Perovskite Solar Cells Go Bifacial-Mutual Benefits for Efficiency and Durability

Bifacial solar cells hold the potential to achieve a higher power output per unit area than conventional monofacial devices without significantly increasing manufacturing costs. However, efficient bifacial designs are challenging to implement in inorganic thin-film solar cells because of their short carrier lifetimes and high rear surface recombination. The emergence of perovskite photovoltaic (PV) technology creates a golden opportunity to realize efficient bifacial thin-film solar cells, owing to their outstanding optoelectronic properties and unique features of device physics. More importantly, transparent conducting oxide electrodes can prevent electrode corrosion by halide ions, mitigating one major instability issue of the perovskite devices. Here, the theory of bifacial PV devices is summarized and the advantages of bifacial perovskite solar cells, such as high power output, enhanced device durability, and low economic and environmental costs, are reviewed. The limitations and challenges for bifacial perovskite solar cells are also discussed. Finally, the awareness of bifacial solar cells as a feasible commercialization pathway of perovskite PV for mainstream solar power generation and building-integrated PV is advocated and future research directions are suggested.