͑Zn,Al͒O thin films have been prepared by a dc reactive magnetron sputtering system with the Al contents in a wide range of 0 -50 at. %. The structural, optical, and electrical properties of ͑Zn,Al͒O films were detailedly and systematically studied. The amount of Al in the film was nearly the same as, but often lower than, that in the sputtering target. The growth rate of films monotonically decreased as the Al content increased. In a low Al content region ͑Ͻ10 at. % ͒, Al-doped ZnO ͑AZO͒ thin films could be obtained at 400°C in an Ar-O 2 ambient with good properties. The optimal results of n-type AZO films were obtained at an Al content of 4 at. %, with low resistivity ϳ10 −4 ⍀ cm, high transmittance ϳ90% in the visible region, and acceptable crystal quality with a high c-axis orientation. The band gap could be widened to 3.52 eV at 4 at. % Al due to the Burstein-Moss shift ͓E. Burstein, Phys. Rev. 93, 632 ͑1954͔͒ modulated by many-body effects. An appropriate Al-doping concentration served effectively to release the residual, compressive stress in film, which may be the reason for the improvement in film stability and the increment in grain size as well. In a medium Al content region ͑10-30 at. % ͒, however, the film quality was degraded, which was presumably due to the formation of clusters or precipitates in the grains and boundaries. Besides the ͑002͒ plane, other diffraction peaks such as ͑100͒ and ͑101͒ planes of ZnO were observed, but the ͑Zn,Al͒O films still exhibited a single-phase wurtzite ZnO structure. An intragrain cluster scattering mechanism was proposed to interpret the reduction of carrier mobility in films with the Al contents in the 7 -20 at. % region. The solubility limit of Al in ZnO film was identified to be in the 20-30 at. % range, much higher than the thermodynamic solubility limit of 2 -3 at. % in ZnO. In a high Al content region ͑ജ30 at. % ͒, there were distinct observations for ͑Zn,Al͒O films. As the Al content was 30 at. %, the film appeared in a two-phase nature with ZnO hexagonal and Al 2 O 3 rhombohedral structures. At the 50 at. % Al content, the matrix of the ͑Zn,Al͒O film was Al 2 O 3 , and no evident trace of wurtzite ZnO was observed. The electrical and optical properties for both cases were also very different from those at the Al contents below 30 at. %.

Inkjet printing (IJP) technology, adapted from home and office printing, has proven to be an essential research tool and industrial manufacturing technique in a wide range of printed electronic technologies, including optoelectronics. Its primary advantage over other deposition methods is the low-cost and maskless on-demand patterning, which offers unmatched freedom-of-design. Additional benefits include the efficient use of materials, contactless high-resolution deposition, and scalability, enabling rapid translation of learning from small-scale, laboratory-based research into large-scale industrial roll-to-roll manufacturing. In the development of organic solar cells (OSCs), IJP has enabled the printing of many of the multiple functional layers which comprise the complete cell as part of an additive printing scheme. Although IJP is only recently employed in perovskite solar cell (PeSC) fabrication, it is already showing great promise and is anticipated to find broader application with this class of materials. As OSCs and PeSCs share many common functional materials and device architectures, this review presents a progress report on the IJP of OSCs and PeSCs in order to facilitate knowledge transfer between the two technologies, with critical analyses of the challenges and opportunities also presented.

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