© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1504 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Pichaya Pattanasattayavong, Nir Yaacobi-Gross, Kui Zhao, Guy Olivier Ngongang Ndjawa, Jinhua Li, Feng Yan, Brian C. O’Regan, Aram Amassian,* and Thomas D. Anthopoulos* Hole-Transporting Transistors and Circuits Based on the Transparent Inorganic Semiconductor Copper(I) Thiocyanate (CuSCN) Processed from Solution at Room Temperature P. Pattanasattayavong, Dr. N. Yaacobi-Gross, Prof. T. D. Anthopoulos Centre for Plastic Electronics and Department of Physics Blackett Laboratory Imperial College London, London SW7 2AZ, UK E-mail: t.anthopoulos@ic.ac.uk Dr. K. Zhao, G. O. Ngongang Ndjawa, Prof. A. Amassian Materials Science and Engineering Division of Physical Sciences and Engineering King Abdullah University of Science and Technology Thuwal 23955-6900, Saudi Arabia E-mail: aram.amassian@kaust.edu.sa J. Li, Prof. F. Yan Department of Applied Physics and Materials Research Centre The Hong Kong Polytechnic University Hong Kong, China Dr. B. C. O’Regan Centre for Plastic Electronics and Department of Chemistry Imperial College London London SW7 2AZ, UK DOI: 10.1002/adma.201202758 Wide-bandgap semiconductors that are easy to process over large-area substrates hold great potential for numerous opto/ electronic applications where optical transparency and charge transport are concurrently required. For example, they can be used as transparent charge-transporting layers in applications such as photovoltaics [1] and light-emitting diodes. [2] A well- known family of wide-bandgap semiconductors is metal oxides, with TiO 2 and ZnO being amongst the most studied mate- rials. [3–5] An important attribute of many metal oxides is their processing versatility. For instance, they can be deposited at low temperatures using solution-based techniques such as ink-jet printing, [6] spin-casting [7] and spray-coating, [8] onto different types of substrates (e.g., glass or plastic), hence offering some capabilities similar to those encountered in other emerging technologies such as organic semiconductors. [9] A further appli- cation area of enormous interest is thin-film transistors (TFTs) for large-area microelectronics such as driving backplanes for organic light-emitting diode (OLED) displays, [10–13] where in a short period of time oxide semiconductors have man- aged to outperform, in terms of discrete device performance, incumbent technologies such as hydrogenated amorphous silicon (a-Si:H), [14] and they are now fast approaching the per- formance level achieved by more advanced technologies such as polycrystalline silicon (poly-Si) TFTs. [15–17] Despite the tre- mendous progress, however, further development in trans- parent microelectronics, based either on oxides or alternative materials, is hindered by the generic lack of hole-transporting (p-type) semiconductors with charge transport characteristics comparable to those found in their n-type counterparts. [13,18–21] At present, most of the reported p-type oxide TFTs are based on either Cu 2 O [18,19] or SnO x . [20,21] Cu 2 O has a bandgap of only ≈2.1 eV, appearing as yellow or red and yielding TFTs with poor performance. SnO x on the other hand has emerged as a more promising candidate with TFTs showing good characteristics, and its optical bandgap is generally reported as 2.5–3.0 eV; however, a closer look at the absorption spectrum suggests that it has an indirect gap at a much lower energy, ≈0.7 eV. [22] The delafossite family CuMO 2 (M = Al, Ga, or In) is another group of materials which have attained significant interest as trans- parent p-type semiconductors. [23] Despite a surge of research effort, no electronic devices based on such materials have been reported so far. Thus, discovery and/or development of new p-type wide-bandgap transparent semiconductors with appreci- able transport characteristics and processing versatility would be required for the development of next generation, inexpen- sive large-area opto/electronics. One interesting inorganic molecular compound that has so far found limited use as a transparent hole transporter in photovoltaic devices is the pseudohalide copper(I) thiocyanate (CuSCN). [24–26] CuSCN is one of the very few known com- pounds that exhibits both high optical transparency – a direct consequence of its wide bandgap (3.7–3.9 eV) [27–30] – and sig- nificant p-type conductivity. [24,25,31,32] Most importantly, CuSCN is inexpensive and can be processed from solution using suit- able solvents at room temperature, [33] thus making it an ideal candidate for application in transparent electronics fabricated using high throughput manufacturing processes onto inexpen- sive flexible plastic substrates. In spite of its attractive charac- teristics, however, the use of CuSCN has yet to be explored for thin-film transistor applications. Here, we report the development of transparent p-type TFTs and unipolar logic circuits based on solution-processed films of Adv. Mater. 2013, 25, 1504–1509