Elucidating Charge Generation in Green-Solvent Processed Organic Solar Cells

High-Performance All-Small-Molecule Organic Solar Cells Fabricated via Halogen-Free Preparation Process

Small-molecule organic photovoltaic materials attract more attention attributing to their precisely defined structure, ease of synthesis, and reduced batch-to-batch variations. The majority of all-small-molecule organic solar cells (ASM-OSCs) have traditionally relied on halogenated solvents for dissolving photovoltaic materials as well as used for the additives or solvent vapor annealing. However, these halogen-based processes pose risks to the environment and human health, potentially impeding future commercial production. Herein, we conducted an investigation into the impact of various nonhalogen solvents on the performance of the devices. By selecting the high boiling point solvent toluene, we achieved a desirable phase separation and stable morphology characterized by fibrous crystals within the blend film. Consequently, the power conversion efficiencies of 14.4 and 11.7% were obtained from H31:Y6-based small-area (0.04 cm2) and large-area (1 cm2) devices with steady performance, respectively. This study successfully demonstrated the fabrication of ASM-OSCs without employing halogenated solvent processes, thus offering promising prospects for the commercial production of ASM-OSCs.

Light-Responsive Oligothiophenes Incorporating Photochromic Torsional Switches

We present a quaterthiophene and sexithiophene that can reversibly change their effective π-conjugation length through photoexcitation. The reported compounds make use of light-responsive molecular actuators consisting of an azobenzene attached to a bithiophene unit by both direct and linker-assisted bonding. Upon exposure to 350 nm light, the azobenzene undergoes trans-to-cis isomerization, thus mechanically inducing the oligothiophene to assume a planar conformation (extended π-conjugation). Exposure to 254 nm wavelength promotes azobenzene cis-to-trans isomerization, forcing the thiophenic backbones to twist out of planarity (confined π-conjugation). Twisted conformations are also reached by cis-to-trans thermal relaxation at a rate that increases proportionally with the conjugation length of the oligothiophene moiety. The molecular conformations of quaterthiophene and sexithiophene were characterized by using steady-state UV-vis spectroscopy, X-ray crystallography and quantum-chemical modeling. Finally, we tested the proposed light-responsive oligothiophenes in field-effect transistors to probe the photo-induced tuning of their electronic properties.

Studies on the Structure, Optical, and Electrical Properties of Doped Manganese (III) Phthalocyanine Chloride Films for Optoelectronic Device Applications

In the last few years, significant advances have been achieved in the development of organic semiconductors for use in optoelectronic devices. This work reports the doping and deposition of semiconducting organic thin films based on manganese (III) phthalocyanine chloride (MnPcCl). In order to enhance the semiconducting properties of the MnPcCl films, different types of pyridine-based chalcones were used as dopants, and their influence on the optical and electric properties of the films was analyzed. The morphology and structure of the films were studied using IR spectroscopy and scanning electron microscopy (SEM). Optical properties of MnPcCl–chalcone films were investigated via UV–Vis spectroscopy, and the absorption spectra showed the Q band located between 630 and 800 nm, as well as a band related to charge transfer (CT) in the region between 465 and 570 nm and the B band in the region between 280 and 460 nm. Additionally, the absorption coefficient measurements indicated that the films had an indirect transition with two energy gaps: the optical bandgap of around 1.40 eV and the fundamental gap of around 2.35 eV. The electrical behavior is strongly affected by the type of chalcone employed; for this reason, electrical conductivity at room temperature may vary from 1.55 × 10−5 to 3.02 × 101 S·cm−1 at different voltages (0.1, 0.5, and 1.0 V). Additionally, the effect of temperature on conductivity was also measured; electrical conductivity increases by two orders of magnitude with increasing temperature from 25 to 100 °C. The doping effect of chalcone favors electronic transport, most likely due to its substituents and structure with delocalized π-electrons, the formation of conduction channels caused by anisotropy, and the bulk heterojunction induced by the dopant. In terms of optical and electrical properties, the results suggest that the best properties are obtained with chalcones that have the methoxy group as a substituent. However, all MnPcCl–chalcone films are candidates for use in optoelectronic devices.