The delafossite structured CuCrO 2 system is well known as one of the best performing p-type transparent conducting oxides. In this paper the details of a low temperature facile growth method for CuCrO 2 is described. The dependence of the growth on the precursors, the temperature and oxygen partial pressure are examined. The decomposition routes are critical to obtain the best performing films. The thermopower and electrical measurements indicate p-type films with conductivity ranging from 1-12 Scm −1 depending on the growth conditions. This p-type conductivity is retained despite the nanocrystallinity of the films. The figure of merit of these films can be as high as 350 µS, which is the best performing p-type TCO by solution methods to date. The optical properties are also investigated using ellipsometry and UV-Vis spectroscopy.

Epitaxial p-type transparent conducting oxide (TCO) Cr 2 O 3 :Mg was grown by electron-beam evaporation in a molecular beam epitaxy system on c-plane sapphire. The influence of Mg dopants and the oxygen partial pressure were investigated by thermoelectric and electrical measurements. The conduction mechanism is analyzed using the small-polaron hopping model, and hopping activation energies have been determined, which vary with doping concentration in the range of 210-300 ± 5 meV. Films with better conductivity were obtained by postannealing. The effect of postannealing is discussed in terms of a crystallographic reordering of the Mg dopant. The highest Seebeck mobilities obtained from thermoelectric measurements are of the order of 10 −4 cm 2 V −1 s −1 . We investigate the fundamental properties of a Mg dopant in a high crystalline quality epitaxial film of a binary oxide, helping us understand the role of short range crystallographic order in a p-type TCO in detail.

In this letter we demonstrate a low temperature (≈ 345 • C) growth method for Cu deficient CuCrO 2 performed by spray pyrolysis using metal-organic precursors and a simple air blast nozzle. Smooth films were grown on glass substrates with a highest conductivity of 12 S/cm. The most conductive samples retain transparencies above 55% resulting in a figure of merit as high as 350 µS, which is the best performing p-type transparent conducting material grown by solution methods to date. Remarkably despite the nano-crystallinity of the films, properties comparable with crystalline CuCrO 2 are observed. No postannealing of the films is required in contrast to previous reports on crystalline material. The low processing temperature of this method means the material can be deposited on flexible substrates. As this is a solution based technique it is more attractive to industry as physical vapour deposition methods are slow and costly in comparison.p-type transparent conducting materials (TCMs) are sought after for optoelectronic devices. Currently commercially available n-type TCMs, such as indium tin oxide (ITO), possess conductivities as high as 1000 S/cm with transparencies greater than 80%. 1 Potential applications that require p-type materials with similar properties include transparent p-n junctions, which would allow for fully-transparent displays. 2 Alternatively, they can be used to minimize shunting as hole injection/extraction layers in light-emitting diodes/solar cells. 3,4 The main interest in this field originated from the potential of the delafossites with the A 1+ B 3+ O 2 lattice structure first highlighted in 1997 when CuAlO 2 was reported to exhibit ptype conductivity while maintaining high transparency. 5 Since then the field has extended to other materials such as oxychalcogenides, spinels and α-Cr 2 O 3 . 6-9 One of the delafossites, CuCrO 2 , has shown promise as a p-type TCM due to reports of high conductivity when doped with Mg. 10 However this is typically only achieved by physical vapour deposition (PVD) which is a relatively slow and costly technique in comparison to other depostion methods. CuCrO 2 has also been grown by chemical vapour deposition (CVD) using the metal-organic Acetylacetonate (acac) precursors Cr(acac) 3 and Cu(acac) 2 at 550 • C, resulting in polycrystalline films with conductivity of 0.86 S/cm (figure of merit (FOM) ≈ 45 µS). 11 Spray pyrolysis (SP) is an inexpensive technique that is suited to depositing films over a large area. Mg-doped films of CuCrO 2 have been synthesized by SP using the same acac precursors with the Mg(acac) 2 precursor for doping. Only after postannealing at 700 • C did they achieve conductivities of 0.6-1 S/cm. 12,13 CuCrO 2 :Zn grown by solgel processing show conductivities of around 0.47 S/cm after two postannealing steps. 14 The high temperature required by these methods is a major drawback for using a) Electronic mail: lefarrel@tcd.ie the material in practical devices. In this letter SP was used to grow thin (50-100 nm) Cu deficient CuCrO 2 film...