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Two-dimensional (2D) tin halide perovskites are promising semiconductors for field-effect transistors (FETs) owing to their fascinating electronic properties. However, the correlation between the chemical nature of organic cations and charge carrier transport is still far from understanding. In this study, the influence of chain length of linear alkyl ammonium cations on film morphology, crystallinity, and charge transport in 2D tin halide perovskites is investigated. The carbon chain lengths of the organic spacers vary from propylammonium to heptanammonium. The increase of alkyl chain length leads to enhanced local charge carrier transport in the perovskite film with mobilities of up to 8 cm2V−1s−1, as confirmed by optical-pump terahertz spectroscopy. A similar improved macroscopic charge transport is also observed in FETs, only to the chain length of HA, due to the synergistic enhancement of film morphology and molecular organization. While the mobility increases with the temperature rise from 100 K to 200 K due to the thermally activated transport mechanism, the device performance decreases in the temperature range of 200 K to 295 K because of ion migration. These results provide guidelines on rational design principles of organic spacer cations for 2D tin halide perovskites and contribute to other optoelectronic applications.

Understanding interface-related phenomena is important for improving the performance of thin-film solar cells. In ACS Appl. Mater. Interfaces2021, 13, 12603–12609, Pranav et al. report that incorporating a thin C60interlayer at the MoO3anode results in reduced surface recombination of electrons, which is ascribed to a decreased electron accumulation near the anode on account of an increased built-in voltage. Here, we offer an alternative explanation: the introduction of a C60interlayer renders the MoO3contact Ohmic. The reduced anode barrier simultaneously increases the built-in voltage, minimizes nonradiative voltage losses upon the extraction of majority carriers (holes), and suppresses minority-carrier (electron) surface recombination, the latter being the result of hole accumulation and associated band bending near the Ohmic hole contact. We therefore argue that Ohmic contact formation suppresses both majority- and minority-carrier surface recombination losses, whereas the built-in voltage per se does not play a major role in this respect.

Controlling crystal growth and reducing the number of grain boundaries are crucial to maximize the charge carrier transport in organic–inorganic perovskite field-effect transistors (FETs). Herein, the crystallization and growth kinetics of a Sn(ii)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, were effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm2V−1s−1to 16 cm2V−1s−1, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing, improve substantially with larger grain size. The optimized 2D (TEA)2SnI4transistor exhibits hole mobility of up to 0.34 cm2V−1s−1at 295 K and a higher value of 1.8 cm2V−1s−1at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.

In amorphous organic semiconductor devices, electrons and holes are transported through layers of small organic molecules or polymers. The overall performance of the device depends both on the material and the device configuration. Measuring a single device configuration requires a large effort of synthesizing the molecules and fabricating the device, rendering the search for promising materials in the vast molecular space both nontrivial and time-consuming. This effort could be greatly reduced by computing the device characteristics from the first principles. Here, we compute transport characteristics of unipolar single-layer devices of prototypical hole- and electron-transporting materials, N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) using a first-principles multiscale approach that requires only the molecular constituents and the device geometry. This approach of generating a digital twin of the entire device can be extended to multilayer stacks and enables the computer design of materials and devices to facilitate systematic improvement of organic light-emitting diode (OLED) devices.

Solution processable organic semiconductors (OSCs) hold advantages for the fabrication of flexible and large-area electronic devices. Meniscus-guided coating (MGC) is one promising technique to tune the crystallization and thin film morphology of OSCs. In this work, we demonstrate the crucial role of the meniscus shape in the fluid flow and crystallization of OSCs during MGC. We demonstrate that angle-dependent dip-coating (ADDC) allows precise control of the meniscus shape. The use of a small meniscus angle during ADDC of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) enhances the crystallization and mass deposition of the OSC due to an increased upward fluid flow. The resulting aligned crystalline film with high surface coverage favors the charge carrier transport in C8-BTBT based field-effect transistors. This work provides comprehensive insight into the fundamental mechanism of OSC crystallization during MGC, which is important for the large-area deposition of OSCs for practical electronic applications.

Macromolecular organic photocatalysts consisting of a completely conjugated network have broad and promising applications in visible light-promoted photoredox catalysis. Precise reproduction and control of exact conjugation length remains an important challenge for fully conjugated and macromolecular photocatalysts. Here, we introduce a new photocatalytic material based on classical PMMA copolymerised with defined electron donor and acceptor units with precisely controllable redox potential and conjugation length, creating a promising class of metal-free, stable and low-cost heterogeneous photocatalysts. Furthermore, swelling of the PMMA copolymer matrix in organic solvents led to enhanced substrate diffusion and thereby increased catalytic efficiency. High efficiency and selectivity was achieved for photocatalytic [4 + 2] cycloaddition reactions in air with low effective photocatalyst loading. The photocatalytic efficiency of the PMMA photocatalyst was comparable with the state-of-the-art metal or non-metal catalysts while facilitating easy recyclability.