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The effect of thermal annealing on the energy levels of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) films was investigated using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and low-energy inverse photoemission spectroscopy. We observed that thermal annealing at 150 °C induces reductions of both the ionization potential (IP) and the electron affinity (EA) with a narrowing of the band gap by 0.1 eV. These changes are associated with crystallization and a 2.54% reduction in the film thickness. Precise measurements of both the IP and EA enabled an evaluation of the effects of the electronic polarization energy in a model based on the charge localized in a single PCBM molecule.

The charge generation and recombination dynamics in fullerene-attached poly(3-hexythiophene) (P3HT)-based diblock copolymer were studied in comparison with those in blend films of P3HT and a fullerene derivative (PCBM) in order to understand the potential advantage of diblock copolymer-based polymer solar cells. Upon photoexcitation, P3HT singlet excitons are promptly converted to P3HT polarons with a time constant of ∼30 ps in both P3HT-PCBM diblock copolymer and P3HT/PCBM blend films. This similar charge generation dynamics is indicative of analogous phase-separated morphology both in these films on a scale of nanometers. After the charge generation, a part of polarons in disorder phases geminately recombine to the ground state in diblock copolymer films, while no geminate recombination is observed in blend films. This geminate recombination loss is probably due to defects of phase-separated structures in diblock copolymer films. On the other hand, charge carrier lifetime is as long as 15 μs in diblock copolymer films. Such a long carrier lifetime may result in a relatively high fill factor in P3HT-PCBM copolymer films. Finally, we discuss the overall device performance in terms of phase-separated structures.

We have developed a new method to fabricate an array of TiO2nanorod assemblies on a flat TiO2surface. The TiO2nanostructures with a height of approximately 40 nm were synthesized via a low temperature sol−gel reaction in a reversed micelle system. Cross-sectional transmission electron microscopy observation revealed that each nanostructure is an assembly of nanorods with a diameter and length of approximately 4 nm and approximately 40 nm, respectively. The fabricated array of TiO2nanorods was applied to construct photovoltaic devices combined with a semiconducting polymer. When the nanostructured TiO2substrate is used, photovoltaic performance reaches a power conversion efficiency of 0.39% and a fill factor of 0.47 under AM 1.5 illumination. Dependence of external quantum efficiency on polymer thickness showed the maximum efficiency in a thicker polymer film condition in the presence of the TiO2nanorod assembly, indicating the nanostructure functions as an efficient exciton collector.

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Perovskite interfaces critically influence the final performance of the photovoltaic devices. Optimizing them by reducing the defect densities or improving the contact with the charge transporting material is key to further enhance the efficiency and stability of perovskite solar cells. Inverted (p–i–n) devices can particularly benefit here, as evident from various successful attempts. However, every reported strategy is adapted to specific cell structures and compositions, affecting their robustness and applicability by other researchers. In this work, we present the universality of perovskite top surface post-treatment with ethylenediammonium diiodide (EDAI2) for p–i–n devices. To prove it, we compare devices bearing perovskite films of different composition, i.e., Sn-, Pb-, and mixed Sn–Pb-based devices, achieving efficiencies of up to 11.4, 22.0, and 22.9%, respectively. A careful optimization of the EDAI2thickness indicates a different tolerance for Pb- and Sn-based devices. The main benefit of this treatment is evident in the open-circuit voltage, with enhancements of up to 200 mV for some compositions. In addition, we prove that this treatment can be successfully applied by both wet (spin-coating) and dry (thermal evaporation) methods, regardless of the composition. The versatility of this treatment makes it highly appealing for industrial application, as it can be easily adapted to specific processing requirements. We present a detailed experimental protocol, aiming to provide the community with an easy, universal perovskite post-treatment method for reliably improving the device efficiency, highlighting the potential of interfaces for the field.

Three isomeric derivatives of 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) bearing ethyl groups on the N-phenyl moieties were synthesized to elucidate the effects of intramolecular interactions on spontaneous orientation polarization (SOP) in thin films. The films of the TPBi derivatives displayed enhanced SOP with a surface potential change of up to 1.8 times that for TPBi, and the p-substituted derivative exhibited the largest potential change reported to date (+141.0 mV/nm). Density functional theory calculations and single-crystal structure analysis suggest that the introduction of the ethyl groups switched the stable molecular conformation from C1to C3symmetry. Through analysis of the structural anisotropy in the films by spectral ellipsometry and two-dimensional (2D) grazing-incidence wide-angle X-ray scattering, we conclude that the conformational change of the molecules was the major factor underlying the SOP enhancement.