Optical iris application of electrochromic thin films

Abstract

We have successfully developed an electrochromic device (ECD) as the “optical iris” of a camera lens that could potentially control the transmittance intentionally. To realize this goal, we have applied photolithography and subsequent wet etching to fabricate the patterned complementary electrochromic systems where tungsten oxide and prussian blue were electrodeposited. At this point it is important to note that such a device could be directly attached onto a camera lens without any mechanical equipment. In this way the device will reduce power consumption and will be much smaller and thinner which results would also further the miniaturization of cameras.

Introduction

Electrochromic displays (ECDs) have attracted considerable interests due to their potential applications as information display, smart window, optical lens, variable reflectance mirrors, etc., which will bring revolutionary advances in the display technologies, owing to attributes such as high optical contrast ratio, low-power consumption, memory effect, and high electrical stability [1], [2], [3], [4]. Especially, among various electrochromic (EC) materials, complementary tungsten oxide (WO₃) and prussian blue (PB, iron(III) hexacyanoferrate(II)) ECDs (hear after abbreviated as WO₃–PB ECD) as the cathodically and anodically coloring materials, respectively, in combination with Li⁺, K⁺, H⁺ or Na⁺-based electrolytes, have been by far the most extensively studied due to the high percent transmittance change (Δ%T) between their bleached and colored states as well as the good electrical stability in comparison with others [5], [6], [7]. More recently, many researches, therefore, have been focused on the new applications of WO₃–PB ECDs such as miniaturization, selective coloration, and so on.

In this communication, we have attempted to find a way of applying the WO₃–PB ECD practically as an “optical iris” of a camera lens, which can artificially control the amount of light penetrated. The major advantage of such a device is that an optical iris can directly be attached onto the camera lens without any mechanical equipment. Consequently, it could be smaller and thinner, which results in micro-devices and further miniaturization of camera. To realize such a device, we have applied the systematically thin film techniques such as photolithography with properly designed mask and subsequent wet etching methods to fabricate a finely patterned transparent iris onto the indium tin oxide (ITO) glasses where the well-known complementary WO₃ and PB were deposited as working and counter electrodes by electrodepositions. The reason why the photolithography and wet etching techniques were chosen for patterning the ITO glasses was due to their easy process and low error rate for production [8], [9]. To mention the conclusions in advance, the well-defined WO₃–PB ECD with patterning (hereafter abbreviated as patterned WO₃–PB ECD) resulted in the various Δ%Ts from 22% to 91% at 633 nm upon switching. This is, to the best of our knowledge, the first example of ECD for applying as an optical iris of a camera lens with controllable optical transmittance.