Early progress in advancing the record efficiency of perovskite (PVSK) solar cells was made using the n-i-p structure with spiro-OMeTAD as the hole transport layer (HTL). However, only moderate performance has been achieved with spiro-OMeTAD as the HTL in the p-i-n structure. In this work we investigate the growth of alumina by atomic layer deposition (ALD) on a spiro-OMeTAD HTL and show improved perovskite film growth when the deposition is optimized. The film growth and device performance were examined with current-voltage analysis, scanning electron microscopy, X-ray diffraction, steady-state and time-resolved photoluminescence, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry. When the ALD process was optimized, high-quality perovskite films were produced that led to a doubling in the average device efficiency of the p-i-n device with spiro-OMeTAD as the HTL. The improvements are attributed to better PVSK film growth rather than to significant reductions in nonradiative recombination.

Narrow bandgap organic-inorganic lead halide-based perovskites have attracted tremendous attention in photovoltaics due to their advantages of low cost, easy synthesis and high efficiency. Selection of suitable charge transport layers and evaluation of device stability and optimization is necessary for commercialization. Degradation of encapsulated narrow bandgap tin-lead perovskite solar cells made with poly(3,4ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS), poly[3-(6-carboxyhexyl)thiophene-2,5-diyl] (P3CT), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layers (HTLs) in ambient air is investigated using spectroscopic ellipsometry measurements. Optical and structural properties of the perovskite absorber layer remain relatively stable after 10 days of aging in ambient air. External quantum efficiency (EQE) simulations based on spectroscopic ellipsometry determined models identify carrier collection losses when compared with experimental EQE. A fresh device with P3CT HTL has 90 +/- 1 % collection of photogenerated carriers in the perovskite absorber near the front contact interface. 3-, 5-, and 10-days aged devices with P3CT have 88 +/- 1 % collection probability near the front contact interface. Fresh and 3-days aged devices with PEDOT:PSS HTL have 90 +/- 1 % collection of photogenerated carriers in the perovskite absorber near the front contact interface. 5- and 10-days aged devices have 88 +/- 1 % near the front contact interface. Fresh, 3-, 5-, and 10-days aged devices with PTAA HTL have 82 +/- 1 % collection near the front contact interface. Devices with P3CT and PEDOT:PSS HTLs have 2.6 to 4.8 % higher power conversion efficiency and reduced electronic losses compared to a device with a PTAA HTL. Understanding how carrier collection losses, particularly near the front and back contacts, varies with different HTLs is necessary for optimizing perovskite solar cell performance.

An in-depth analysis of the optical properties of epitaxial (001) oriented LaMnO3films grown on SrTiO3and LaAlO3single crystal substrates is performed by spectroscopic ellipsometry to determine the complex dielectric function (ε = ε1 + iε2) spectra from 0.12 to 5.89 eV. Density Functional Theory and many body perturbation theory within the G0W0 and the Bethe-Salpeter Equation approximations, are also employed to generate theoretical spectra in ε. Critical point energies (CPs) from 0.91 to 1.49 eV are interpreted as energy separation between eg and t2g orbitals. CPs from 3.31 to 3.53 eV and 3.75 to 5.23 are interpreted as Mn d exchange splitting and strong charge transfer transitions, respectively. Direct and indirect bandgaps from Tauc-plots are identified in the range of 0.100–0.594 eV. Anisotropy presents in LaMnO3 on LaAlO3 is attributed to substantial distortion in the out-of-plane epitaxial strain compared to LaMnO3 on SrTiO3. These findings provide a comprehensive understanding of the origins and characteristics of features observed in optical properties of epitaxial LaMnO3, offering insights for development of optical and electronic applications based on these materials.

An in-depth analysis of the optical properties of epitaxial (001) oriented LaMnO3 3 films grown on SrTiO3 3 and LaAlO3 3 single crystal substrates is performed by spectroscopic ellipsometry to determine the complex dielectric function (epsilon = epsilon 1 1 + i epsilon 2) 2 ) spectra from 0.12 to 5.89 eV. Density Functional Theory and many body perturbation theory within the G0W0 0 W 0 and the Bethe-Salpeter Equation approximations, are also employed to generate theoretical spectra in epsilon. Critical point energies (CPs) from 0.91 to 1.49 eV are interpreted as energy separation between eg g and t 2g orbitals. CPs from 3.31 to 3.53 eV and 3.75 to 5.23 are interpreted as Mn d exchange splitting and strong charge transfer transitions, respectively. Direct and indirect bandgaps from Tauc-plots are identified in the range of 0.100-0.594 eV. Anisotropy presents in LaMnO3 3 on LaAlO3 3 is attributed to substantial distortion in the out-of-plane epitaxial strain compared to LaMnO3 3 on SrTiO3. 3 . These findings provide a comprehensive understanding of the origins and characteristics of features observed in optical properties of epitaxial LaMnO3, 3 , offering insights for development of optical and electronic applications based on these materials.

Easy‐to‐form tin vacancies at the buried interface of tin‐lead perovskites hinder the performance of low‐bandgap perovskite solar cells (PSCs). Here, a synergistic strategy by incorporating potassium citrate (PC) into the poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole‐transport layer to passivate the buried interface of Sn‐Pb PSCs is reported. PC neutralizes the acidity of PEDOT:PSS and stabilizes the perovskite front surface, enhancing device stability. Citrate moieties coordinate with Sn 2+ on the buried perovskite surface, preventing Sn 2+ oxidation and suppressing defect formation. Additionally, potassium cations incorporate into Sn‐Pb perovskites, enhancing crystallinity and passivating halide defects. The combined benefits enable efficient low‐bandgap Sn‐Pb PSCs with a power conversion efficiency of 22.7% and a high open‐circuit voltage of 0.894 V. Using this method, 26.1% efficiency for all‐perovskite tandem solar cells is demonstrated. These results emphasize the significance of buried interface passivation in developing efficient and stable Sn‐Pb PSCs and all‐perovskite tandem solar cells.

Mixed Pb+Sn narrow bandgap perovskites absorbers are used in high performance in single junction or the bottom junction in tandem solar cells. However, the instability of these materials with exposure to environmental conditions is still a major challenge, and it is necessary to monitor and understand the degradation mechanisms of these perovskites in devices. Spectroscopic ellipsometry measurements and analysis of complete narrow bandgap perovskite-based solar cells are used in combination with external quantum efficiency (EQE) measurements and simulations are used to track changes occurring from initial fabrication to 5 days aging in ambient air. The complex optical property spectra and thicknesses of all component layers of the solar cell are used as input for EQE simulations. No changes are observed in the ellipsometric spectra with aging, indicating that large structural or optical property variations are not occurring. Comparison of initial measured EQE to simulated EQE identifies reduced collection probability of photogenerated carriers in the ~10 nm and ~650 nm of perovskite material near the HTL and ETL interfaces, respectively. The carrier collection probability decreases with the aging of the device. SCAPS simulations indicate that the reduced collection probability and EQE can be attributed to the increase in trap state density with time.

Achromatic quarter waveplates (A-QWPs), traditionally constructed from multiple birefringent crystals, can modulate light polarization and retardation across a broad range of wavelengths. This mechanism is inherently related to phase retardation controlled by the fast and slow axis of stacked multi-birefringent crystals. However, the conventional design of A-QWPs requires the incorporation of multiple birefringent crystals, which complicates the manufacturing process and raises costs. Here, we report the discovery of a broadband (540-1060 nm) A-QWP based on a two-dimensional (2D) layered hybrid copper halide (HCH) perovskite single crystal. The 2D copper chloride (CuCl6) layers of the HCH crystal undergo Jahn-Teller distortion and subsequently trigger the in-plane optical birefringence. Its broad range of the wavelength response as an A-QWP is a consequence of the out-of-plane mosaicity formed among the stacked inorganic layers during the single-crystal self-assembly process in the solution phase. Given the versatility of 2D hybridhalide perovskites, the 2D HCH crystal offers a promising approach for designing cost-effective A-QWPs and the ability to integrate other optical devices.

In situ real-time spectroscopic ellipsometry (RTSE) measurements have been conducted on MAPbI3, MA0.7FA0.3PbI3, and (FAPbI3)0.95(MAPbBr3)0.05 perovskite thin films when exposed to different levels of relative humidity at given temperatures over time. Analysis of RTSE measurements track changes in the complex dielectric function spectra and structure, which indicate variations in stability influenced by the underlying material, preparation method, and perovskite composition. MAPbI3 and MA0.7FA0.3PbI3 films deposited on commercial fluorine-doped tin oxide coated glass are more stable than corresponding films deposited on soda lime glass directly. (FAPbI3)0.95(MAPbBr3)0.05 films on soda lime glass showed improved stability over the other compositions regardless of the substrate, and this is attributed to the preparation method as well as the final composition.