**2. Materials and Methods**

Al-doped ZnO films were deposited using an ALD Beneq TFS-200 system (Espoo, Finland). Trimethylaluminum (TMA) and diethylzinc (DEZ) were purchased from Strem Chemicals, Inc. (Bischheim, France), and used as received. These precursors and distilled water were held at room temperature in stainless steel containers for all depositions. Purge and line flows used pure N2 (600 sccm for TMA, DEZ, and water). The precursors' pulse durations were the same for DEZ, TMA, and H2O—200 ms, while the purging time after each precursor was 2 s, for all deposition runs. In all depositions, the TMA pulse was introduced after a DEZ pulse/purge cycle, in order to minimize the impact of the TMA pulse on the growth rate [21]. The Al-doping of ZnO was controlled by varying the number of DEZ/H2O and TMA/H2O pulses [22]. In a typical deposition procedure, after each 24 cycles of DEZ/H2O, a cycle of TMA/H2O was applied consisting one so-called supercycle. The desired film thickness was controlled by the number of supercycles. The depositions were performed with the substrate holder temperature of 200 ◦C for AZO/glass and 100 ◦C for AZO/PET. The structural, optical and electrical properties of ALD Al-doped ZnO films were measured by using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), spectrophotometry and a four-point probe method.

Additionally, in the case of AZO deposition on PET substrates, a buffer film of amorphous Al2O3 (ALO) was deposited in situ at the same temperature of 100 ◦C. The buffer film prevents the diffusion of the next precursors in the pores of the PET substrate. For ALO buffer deposition, the same precursors (TMA/H2O) were used with the same pulse durations and purging times and 88 repetitions of the TMA/H2O cycle.

The AZO film thickness was determined by ellipsometric measurements using a Woollam M2000D rotating compensator spectroscopic ellipsometer (Lincoln, MI, USA) with a wavelength range from 193 to 1000 nm in reflection mode. For AZO/glass, the thickness was 206 nm and for AZO/PET the thickness was approximately 100 nm. The Al2O3 buffer film deposited on PET substrates as barrier to prevent diethylzinc diffusion into the polymer substrate [23] was approximately 15-nm thick.

The AZO films' surface morphology was analyzed using Atomic Force Microscopy (AFM), MFP-3D, Asylum Research, Oxford Instruments (Abingdon, UK) and Scanning Electron Microscopy (SEM), JEOL (Tokyo, Japan).

The optical transmittance spectra of AZO films deposited on glass and PET in the wavelength range of 200 to 1600 nm were measured at room temperature using an ultraviolet–visible–near-infrared (UV–VIS–NIR) spectrophotometer Cary 5E (Palo Alto, CA, USA). The same measurements were performed on reference glass, PET and ITO/glass substrates for comparison.

The sheet resistance was measured using a four-point probe technique. A computerized home-built bending setup, with an ESP301 control platform (Newport, Irvine, CA, USA) with the function to stimulate bending at different radii, was used for the bending tests of flexible samples. The sheet resistance was tested in the interval of up to 1000 bending cycles.

Several AZO films deposited on glass and PET were selected for the LC and PDLC device assembly. The LC and PDLC device fabrication procedure is described in detail in Section 3.2: Applications. The electro-optical characteristics of fabricated LC and PDLC devices were measured by positioning the assembled cell in the optical setups, also described in detail in the same section.
