We report the characteristics of Al-doped zinc oxide (AZO) films prepared by a highly efficient cylindrical rotating magnetron sputtering (CRMS) system for use as a transparent conducting electrode in cost-efficient bulk hetero-junction organic solar cells (OSCs). Using a rotating cylindrical type cathode with an AZO target, whose usage was above 80%, we were able to obtain a low cost and indium free AZO electrode with a low sheet resistance of ∼4.59 Ω/sq, a high transparency of 85% in the visible wavelength region and a work function of 4.9 eV at a substrate temperature of 230 °C. Moreover, the neutral poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) based OSC fabricated on the CRMS-grown AZO electrode at 230 °C showed an open circuit voltage of 0.5 V, a short circuit current of 8.94 mA cm−2, a fill factor of 45% and power conversion efficiency of 2.01%, indicating that CRMS is a promising cost-efficient AZO deposition technique for low cost OSCs.

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Composition-dependent changes in the properties of Ga-doped ZnO (GZO) transparent conductive oxide (TCO) films were investigated by preparing a series of GZO films on glass substrates via pulsed dc magnetron sputtering with ZnO ceramic targets having various Ga 2 O 3 concentrations at various temperatures. As the Ga 2 O 3 content in the target increased, crystalline quality was improved as revealed in the intense ZnO (0 0 2) diffraction peaks, which accompanied increased carrier concentrations. When the Ga 2 O 3 content was low, it was deduced from the crystallinity and carrier concentration that Ga or its oxide species functioned primarily as a crystal growth promoter, which was more distinctive at lower deposition temperatures. Meanwhile, formation of the secondary oxide phases, detrimental to the carrier mobility, was rather enhanced up to intermediate temperature and then suppressed by further increasing the deposition temperature. Consequently, improved crystallinity and enhanced doping efficiency and therefore the lowest electrical resistivity could be achieved with the combination of higher Ga 2 O 3 content in the target and higher deposition temperature. Electrical resistivity and optical transmittance of the GZO films prepared by the pulsed dc magnetron sputtering in this study fulfilled requirements for TCO films.

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