Polymer‐based photovoltaic cells, with periodic sub‐micrometer structures as an efficient light‐trapping scheme, are investigated to improve the performance of organic solar cells based on poly(3‐hexylthiophene) and 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl‐(6,6)C61. A soft lithographic approach that uses photoresponsive azo polymer films as masters and poly(dimethylsiloxane) as stamps is used to form surface relief gratings (SRGs) on the active layers. The effect of periodic gratings on solar cell performance is precisely investigated according to various grating conditions such as period, depth, and dimension. The solar cells with 1D and 2D SRGs present improved incident‐photon‐to‐current conversion efficiencies and an overall increase in power conversion efficiencies, primarily resulting from the enhancement of short‐circuit current density, indicating that periodic structures induce further photon absorption in the active film.

In this report, we investigate a formation mechanism for polymer chains aligned with various semiconductor polymers, and a microstructure for directionally aligned film through systematic analysis that includes polarized UV-visible-Near Infrared (UV-vis-NIR) absorption spectroscopy, atomic force microscope, polarized charge modulation microscopy (p-CMM), and incident X-ray diffraction (GIXD) measurements. Through this study, we make two important observations: first, the highly aligned organic polymer semiconductor films are achieved by off-center spin coating of the pre-aggregated conjugated polymer solution. Second, the directionally aligned conjugated polymer films exhibit a larger anisotropy on the top surface compared with bulk film, which allows effective mobility improvement in top-gate/bottomcontact field-effect transistors with high performance uniformity. Finally, we demonstrate highmobility organic field-effect transistors (OFETs) (7.25 cm 2 /Vs) with a mobility large anisotropy (37-fold) using poly[(E)-1,2-(3,3′-dioctadecyl-2,2′-dithienyl)ethylene-alt-dithieno-(3,2-b:2′,3′-d)thiophene] (P18) as the semiconductor layer.

The preparation of a reduced graphene oxide (pr‐Go) is with a novel p‐TosNHNH2 reductant is demonstrated for use as an efficient anode interfacial layer for high‐performance and highstability organic solar cells (OSCs). The efficiency of the cells with pr‐GO is highly comparable to those of the PEDOT:PSSbased devices. Furthermore, the pr‐GO based OSCs show a much longer cell life time in air stability tests in comparison with PEDOT:PSS‐based cells.

Large-area polymer FET arrays and integrated circuits (ICs) are successfully demonstrated via a simple wire-bar-coating process. Both a highly crystalline conjugated polymer layer and very smooth insulating polymer layer are formed by a consecutive wire-bar-coating process on a 4-inch plastic substrate with a short processing time for application as the active and dielectric layers of OFET arrays and ICs.

High‐performance top‐gated organic field‐effect transistor (OFET) memory devices using electrets and their applications to flexible printed organic NAND flash are reported. The OFETs based on an inkjet‐printed p‐type polymer semiconductor with efficiently chargeable dielectric poly(2‐vinylnaphthalene) (PVN) and high‐k blocking gate dielectric poly(vinylidenefluoride‐trifluoroethylene) (P(VDF‐TrFE)) shows excellent non‐volatile memory characteristics. The superior memory characteristics originate mainly from reversible charge trapping and detrapping in the PVN electret layer efficiently in low‐k/high‐k bilayered dielectrics. A strategy is devised for the successful development of monolithically inkjet‐printed flexible organic NAND flash memory through the proper selection of the polymer electrets (PVN or PS), where PVN/‐ and PS/P(VDF‐TrFE) devices are used as non‐volatile memory cells and ground‐ and bit‐line select transistors, respectively. Electrical simulations reveal that the flexible printed organic NAND flash can be possible to program, read, and erase all memory cells in the memory array repeatedly without affecting the non‐selected memory cells.

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (∼4.1 eV) compared to that of a pristine Au electrode (∼4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ∼0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ∼0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ∼12 kHz) based on a solution-processed ambipolar polymer are demonstrated.

The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air.

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