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
_it
≈ 8.0 × 10
¹¹
eV
^-1
cm
^-2
) and neutral level (E
_o
≈ -5.2 eV). These devices have exhibited a photoconductive behavior at λ = 365 nm, and low-noise Ag-ZnO detectors have exhibited the responsivity (R) and photoconductivegain (G) of 1.93×10
^-4
A/W and 6.57×10
^-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
_oc
) was 1.2 V and short-circuit current density (J
_sc
), due to minority carrier tunneling, was 0.68 mA/cm
²
.