ZnO-Based Schottky and Oxide Multilayer Devices for Visibly Transparent Photovoltaic Applications

Autonomous smart windows may be integrated with a stack of active components, such as electrochromic devices, to modulate the opacity/transparency by an applied voltage. This voltage may be generated with a visibly transparent photovoltaic device. This paper describes the processing and performance of zinc oxide (ZnO) films for integration with electrochromic stacks. Sputtered ZnO (2% Mn) films on indium-tin oxide with transparency in the visible range were used to fabricate metal-semiconductor (MS), metal-insulator-semiconductor, and p-i-n heterojunction devices, and their photovoltaic conversion under ultraviolet (UV) illumination was evaluated with and without oxygen plasma-treated surface electrodes (Au, Ag, Al, and Ti/Ag). The MS Schottky parameters were fit against the generalized Bardeen model to obtain the density of interface states ( {D}_{\textsf {it}} \approx \textsf {8.0}\times \textsf {10}^{\textsf {11}} eV −1 cm −2 ) and neutral level ( {E}_{o} \approx -\textsf {5.2} eV). These devices have exhibited a photoconductive behavior at \lambda = \textsf {365} nm, and low-noise Ag-ZnO detectors have exhibited the responsivity ( {R} ) and photoconductive gain ( {G} ) of \textsf {1.93}\times \textsf {10}^{-\textsf {4}} A/W and \textsf {6.57}\times \textsf {10}^{-\textsf {4}} , respectively. Confirmed via matched-pair analysis, postmetallization oxygen plasma treatment of Ag and Ti/Ag electrodes has resulted in increased Schottky barrier heights, which maximized with a 2-nm SiO 2 electron blocking layer, coupled with the suppression of recombination at the MS interface and blocking of majority carriers. For interdigitated devices under monochromatic UV-C illumination, the open-circuit voltage ( {V}_{\textsf {oc}} ) was 1.2 V and short-circuit current density ( {J}_{\textsf {sc}} ), due to minority carrier tunneling, wa