At present there is no ‘ideal’ thin-film transistor technology for demanding display applications, such as organic light-emitting diode displays, that allows combining the low-temperature, solution-processability offered by organic semiconductors with the high level of performance achievable with microcrystalline silicon1. N-type amorphous mixed metal oxide semiconductors, such as ternary oxides Mx1My2Oz, where M1 and M2 are metals such as In, Ga, Sn, or Zn, have recently gained momentum because of their high carrier mobility and stability2, 3 and good optical transparency, but they are mostly deposited by sputtering. So far no route is available for forming high-performance mixed oxide materials from solution at low process temperatures <250 °C. Ionic mixed metal oxides should in principle be ideal candidates for solution-processable materials because the conduction band states derived from metal s-orbitals are relatively insensitive to the presence of structural disorder and high charge carrier mobilities are achievable in amorphous structures2. Here we report the formation of amorphous metal oxide semiconducting thin-films using a ‘sol–gel on chip’ hydrolysis approach from soluble metal alkoxide precursors, which affords unprecedented high field-effect mobilities of 10 cm2 V−1 s−1, reproducible and stable turn-on voltages Von≈0 V and high operational stability at maximum process temperatures as low as 230 °C.

Nanometer-sized particles of the chalcopyrite compounds CuInS 2 and CuInSe 2 were synthesized by thermal decomposition of molecular single-source precursors (PPh 3 ) 2 CuIn-(SEt) 4 and (PPh 3 ) 2 CuIn(SePh) 4 , respectively, in the noncoordinating solvent dioctyl phthalate at temperatures between 200 and 300 °C. The nanoparticles range in size from 3 to 30 nm and are aggregated to form roughly spherical clusters of about 500 nm in diameter. X-ray diffraction of the nanoparticle powders shows greatly broadened lines, indicative of very small particle sizes, which is confirmed by TEM. Peaks present in the XRD can be indexed to reference patterns for the respective chalcopyrite compounds. Optical spectroscopy and elemental analysis by energy dispersive spectroscopy support the identification of the nanoparticles as chalcopyrites.

The electronic structure of low temperature, solution-processed indium–zinc oxide thin-film transistors is complex and remains insufficiently understood. As commonly observed, high device performance with mobility >1 cm2 V−1 s−1 is achievable after annealing in air above typically 250 °C but performance decreases rapidly when annealing temperatures ≤200 °C are used. Here, the electronic structure of low temperature, solution-processed oxide thin films as a function of annealing temperature and environment using a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and photothermal deflection spectroscopy is investigated. The drop-off in performance at temperatures ≤200 °C to incomplete conversion of metal hydroxide species into the fully coordinated oxide is attributed. The effect of an additional vacuum annealing step, which is beneficial if performed for short times at low temperatures, but leads to catastrophic device failure if performed at too high temperatures or for too long is also investigated. Evidence is found that during vacuum annealing, the workfunction increases and a large concentration of sub-bandgap defect states (re)appears. These results demonstrate that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.

deposition processes. Despite impressive progress over the last decade, OPVs are still some way behind other thin-fi lm technologies harvesting solar energy because of low effi ciencies and short lifetimes. [ 5 ] Materials for OPVs such as the semiconducting polymers, transparent electrodes, substrates, and encapsulant materials are not cheap enough to be competitive for large-area power generation. Nevertheless, there are small-scale, energy harvesting applications where OPVs are required to be locally printed to provide electric power to the system. For example, system-in-foil devices could include sensor components, OPVs for energy harvesting, a thin fi lm battery for energy storage, and an organic light-emitting diode (OLED) array as a display and electronic circuitry on a single substrate. [ 6 ] To date, no route is available for monolithically integrating solar cells into a system in which other components such as transistors, sensors, or displays are already fabricated.Here, we report for the fi rst time the fabrication and measurement of all-inkjet-printed, all-air-processed organic solar cells with the structure poly(3,4-ethylenedioxythi ophene):polystyrene sulfonate (PEDOT:PSS)/poly[N-9′heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC 70 BM)/ZnO/Ag. A schematic diagram of the printed solar cell structure and the energy level diagram of its components is presented in Figure 1 . Among the various printing methods, inkjet-printing technology has been selected here for the fabrication of all-printed bulk-heterojunction solar cells because of its capability to locally deposit small volumes of functional inks without a mask and with high positional accuracy and low cost. Inkjet printing has proven effective in fabrication of OLEDs, [ 7 ] thin-fi lm transistors, [ 8 ] and photodetectors, [ 9,10 ] and was recently applied to fabricate either an active layer or an anode of OPVs. [11][12][13][14] We demonstrate a high-effi ciency solar cell with a homogeneous inkjet-printed donor-acceptor thin fi lm which was achieved by engineering the semiconducting blend ink with a tailored ternary solvent. Atomic force microscopy (AFM), grazing incidence wide-angle X-ray scattering (GIWAXS), and transient absorption spectroscopy are used to explore surface morphology, fi lm microstructure, and polaron dynamics in both inkjet-printed and spin-coated PCDTBT:PCBM fi lms. The results have shown that our inkjet-printed blend layer exhibits similar nanoscale structure and excited state dynamics to its spin-coated counterparts.The prospective of using direct-write printing techniques for the manufacture of organic photovoltaics (OPVs) has made these techniques highly attractive. OPVs have the potential to revolutionize small-scale portable electronic applications by directly providing electric power to the systems. However, no route is available for monolithically integrating the energy-harvesting units into a system in which other components, suc...

Cu 1.8 S quantum dots were prepared by using a single-source-precursor type method and investigated in the light of opto-electronic applications. With femtosecond time-resolved transient absorption measurements, the electron relaxation as well as their trapping dynamics could be evaluated. The measurements reveal that the largest and the smallest QD samples prepared exhibit the longest mobility lifetimes, and that the electron-hole relaxation dynamics is strongly dependent on the occurrence of trapping sites. Based on the argument of optical response, it appears that the largest prepared Cu 1.8 S QDs with band gap energy of 2.35 eV are preferred candidates for opto-electronic device fabrication.y Dedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays.

Electron injection from the source–drain electrodes limits the performance of many n‐type organic field‐effect transistors (OFETs), particularly those based on organic semiconductors with electron affinities less than 3.5 eV. Here, it is shown that modification of gold source–drain electrodes with an overlying solution‐deposited, patterned layer of an n‐type metal oxide such as zinc oxide (ZnO) provides an efficient electron‐injecting contact, which avoids the use of unstable low‐work‐function metals and is compatible with high‐resolution patterning techniques such as photolithography. Ambipolar light‐emitting field‐effect transistors (LEFETs) based on green‐light‐emitting poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) and blue‐light‐emitting poly(9,9‐dioctylfluorene) (F8) with electron‐injecting gold/ZnO and hole‐injecting gold electrodes show significantly lower electron threshold voltages and several orders of magnitude higher ambipolar currents, and hence light emission intensities, than devices with bare gold electrodes. Moreover, different solution‐deposited metal oxide injection layers are compared. By spin‐coating ZnO from a low‐temperature precursor, processing temperatures could be reduced to 150 °C. Ultraviolet photoemission spectroscopy (UPS) shows that the improvement in transistor performance is due to reduction of the electron injection barrier at the interface between the organic semiconductor and ZnO/Au compared to bare gold electrodes.

We report a new simplified synthetic procedure for commercial manufacture of ternary single-source precursors (SSPs). This new synthetic process has been successfully implemented to fabricate known SSPs on bulk scale and the first liquid SSPs to the semiconductors CuInSe(2) and AgIn(x)S(y). Single crystal X-ray determination reveals the first unsolvated ternary AgInS SSP. SSPs prepared via this new route have successfully been used in a spray assisted chemical vapor deposition (CVD) process to deposit polycrystalline thin films, and for preparing ternary nanocrystallites.

Stability of organic photovoltaic devices (OPVs) is a limiting factor for their commercialization and still remains a major challenge whilst power conversion efficiencies are now approaching minimum requirements. The inverted organic solar cell (iOSC) architecture shows promising potential for improving significantly the cell's working lifetime. However, when solution processed ZnO is used as electron extraction layer, an undesirable light‐soaking step is commonly required before the device reaches a non‐permanent maximum performance. This work investigates the use of Sr and Ba doped ZnO films, ZnSrO and ZnBaO, formed by sol‐gel deposition using molecular alkoxide precursor solutions, as electron extraction layers in a model iOSCs with poly [3‐hexylthiophene] (P3HT): [6, 6]‐phenyl C60 butyl acid methyl ester (PCBM) as the active layer. We show that using these ternary oxides the light‐soaking step can be circumvented by preventing a dipole forming between the oxide and the active organic layer as supported by electroabsorption spectroscopy measurements of the device built‐in field. It is suggested that Sr or Ba doping results in suppression/reduction of the oxygen adsorption at mobile oxygen vacancy sites on the metal oxide surface. Like in thin film transistor (TFT) applications, where materials like InGaZnO are rapidly becoming an important technology, the use of amorphous, mixed metal oxides allows improving the performance and stability of interfacial charge extraction layers for organic solar cells.