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There were a number of reports on the growth of NR using several kinds of growth techniques. Inorganic nanowires can be synthesized by various methods such as VLS, CVD, thermal oxidation and hydrothermal (Supplementary Table 3). However, VLS, CVD and the thermal oxidation methods required high temperature (greater than 400 °C), which would damage a polymer substrate. The hydrothermal method can grow NRs at low temperatures (about 100 °C), but the growth rate is too slow (less than 1 nm min-1). The high process temperatures and slow rates of the previous methods are serious disadvantages for application to polymer substrates. In this work, we found a way to use a Cl2 plasma source to grow the single-crystalline and vertically well-aligned AgCl NRs. The advantages of this technique are low temperature process (room temperature) and high-growth rate (about 2,000 nm min-1). Such process condition allows the AgCl NRs to implement the R2R process shown in Fig. 1.

To confirm the applicability of the method to R2R process, we designed a virtual roll-to-roll (R2R) system (Supplementary Fig. 10). The plasma exposure time is a critical factor for application to R2R process. The plasma time of 45 s is sufficient to get the NRs (Fig. 2). Because the deposition rate of Ag layer did not have a significant effect on morphology or growth rate of AgCl NRs (Supplementary Fig. 11), the deposition rate was set to be 20 Å s-1.

When the plasma chamber was 90 cm long, and the Ag-deposition chamber was 300 cm long, the feed rate of R2R process was 1.2 m min-1, which could be used in a commercial process. As a result, the plasma-induced AgCl NRs could be rapidly fabricated using an R2R process over a large area on several kinds of polymer film because the method does not require lithography, mask moulds or thermal processes. These size-tunable and plasma-induced AgCl NRs can promote the commercialization of highly efficient, inexpensive flexible optoelectronic devices.

Methods
Fabrication of AgCl NRs
The colourless PI films were ultrasonically cleaned with isopropyl alchol for 5 min, then dried under blowing N2 gas and baked at 110 °C for 10 min. The Ag layer was deposited at 1 Å s-1 on the PI film by using an e-beam evaporator under 1 × 10-6 Torr. Then PI films with Ag layers were treated using Cl2 plasma. The plasma was induced using 350-W RF power in Cl2 ambient. The chamber pressure was maintained at 10 mTorr during treatment.

Characterized instrument
The total and diffused transmittance of the AgCl/PI sample were measured using a ultraviolet–visible–NIR spectrophotometer (Cary 4000, Agilent) with a diffuse reflectance accessory. The surface morphology of the AgCl was measured using a field-emission scanning electron microscope (XL30S FEG, PHILIPS) with an 5 kV acceleration voltage and 6 mm working distance, and an atomic force microscope operated in tapping mode on a Veeco nanoscope III. XPS was measured using a synchrotron radiation photoemission spectroscopy with the incident X-ray source at 650 eV and a base pressure of 5 × 10-10 Torr at the 4D beam line at the Pohang Accelerator Laboratory (PAL). The chemical bonding states were separated using a combination of Gaussian and Lorentzian functions. The XRD patterns were measured using a house X-ray source (D2 phaser, Bruker) at 30 kV and 10 mA. Off-axis phi scans using synchrotron radiation were performed at the 3D beamline at PAL. The HRTEM (JEM 2200FS, JEOL) was conducted at 200 kV with a Cs-corrector. The AgCl NRs were sonicated in ethanol and put in a Cu grid. To prevent e-beam decomposition of the AgCl, 10 nm of carbon was deposited on both sides of the Cu grid.