Aluminum-doped ZnO thin films deposited on flat and nanostructured glass substrates: Quality and performance for applications in organic solar cells

Pontsho Mbule, Dong Wang, Rolf Grieseler, Peter Schaaf, Burhan Muhsin, Herald Hoppe, Bakang Mothudi, Mokhotjwa Dhlamini

Index: 10.1016/j.solener.2018.03.007

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Abstract

Transparent conductive aluminum-doped zinc oxide (AZO) thin films were deposited on a flat and nanostructured borosilicate glass substrates by using DC-magnetron sputtering. The aluminum doping concentration was kept at 3.3 wt% and the film thickness (100–400 nm) was varied. The thin films were then annealed at 250 °C for 1 h in nitrogen and/or argon atmosphere, respectively. AZO thin films exhibited hexagonal wurtzite structure of ZnO with an intense (0 0 2) diffraction peak, indicating that they have c-axis preferred orientation. Optical transmittance was observed to be greater than 80% in the visible range for films deposited on both flat and nanostructured glass substrates. The lowest resistivity of 9.7 × 10−4 Ω cm was observed for AZO film of 400 nm thickness on flat glass substrate, annealed in Nitrogen atmosphere. The power conversion efficiency (PCE) of 0.27% and 2.24% were recorded for organic solar cell devices based on AZO deposited on nanostructured and flat borosilicate glass, respectively. In comparison with the latter, the PCE of ITO based device was recorded to be 3.17%. Due to their good optical and electrical properties, AZO thin films are promising candidates as transparent electrodes in organic solar cells.