Development of Highly Bendable Transparent Window Electrodes Based on MoOx, SnO2, and Au Dielectric/Metal/Dielectric Stacks: Application to Indium Tin Oxide (ITO)-Free Perovskite Solar Cells

Giulia Lucarelli,Thomas M Brown

doi:10.3389/fmats.2019.00310

Giulia Lucarelli, Thomas M Brown

Open Access

https://doi.org/10.3389/fmats.2019.00310

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Journal: Frontiers in materials	Publication Date: Dec 4, 2019
Citations: 22	License type: CC BY 4.0

Affiliation: University of Rome Tor Vergata

Abstract

Indium-doped tin oxide (ITO) is the transparent conductive material of choice for a wide range of optoelectronic devices such as sensors, light-emitting diodes and solar cells. However, its brittle nature, high cost, scarcity as well as aggressive deposition via sputtering determine the need to find cheap alternatives with high optical transparency, low sheet resistance, and mechanical flexibility. Dielectric/metal/dielectric (D/M/D) electrodes fulfill all these requirements and are deposited via low embodied energy low-temperature processing. We developed D/M/D multilayered electrodes based on thermally evaporated MoOx or solution-processed SnO2 seed layers, a thermally evaporated ultrathin Au film, and a spin-coated SnO2 top layer on rigid glass substrates. We first systematically unraveled the role of each layer on the resistance-transmittance properties of the full D/M/D electrode structure. By optimizing the thickness of the seed, metal and the top layer, we obtained electrodes with transmittance of 72% at 550 nm and a minimum sheet resistance of 9  sq-1. Subsequently, these optimized multilayered stacks were employed as bottom electrodes for perovskite solar cells with glass/D/M/D/mesoporous-TiO2/CH3NH3PbI3/spiro-MeOTAD/Au device architecture, delivering power conversion efficiencies (PCE) of 10.7%. Further, we deposited and characterized D/M/D electrodes on flexible polyethylene terephthalate (PET) films, achieving a maximum PCE of 7.6%. The difference in performance compared to rigid glass devices can be ascribed to the different wetting of the active layer on PET substrates. Flexible D/M/D electrodes displayed excellent mechanical properties compared to commercial PET/ITO, showing completely stable sheet resistance after repeated bending even down to 1.5 mm of curvature radius, whereas PET/ITO showed one order of magnitude increase in sheet resistance in the same mechanical test, due to formation of cracks in the conductive oxide. Our optimized D/M/D stacks on glass and especially on PET or other flexible substrates are therefore excellent alternatives to ITO as transparent window electrodes for low-cost, light-weight and conformal optoelectronics applications.

Highlights

Organic-inorganic perovskite solar cells (PSC) are on the rise as the most promising contenders among new generation photovoltaic technologies, due to the outstanding optoelectronic properties of perovskite absorbers (Correa-Baena et al, 2017) as well as associated low-cost and compatibility with large area fabrication processes (Razza et al, 2016)
We investigated the role of each layer on the optical and electrical characteristics of the composite electrodes on both polyethylene terephthalate (PET) and glass substrates
The Role of Seed, Metal, and Top Oxide Layers and Their Combination on the Optical and Electrical Properties of Electrodes Here, we present the effect of each layer and combination of layers of the D/M/D stack on both the transmittance and sheet resistance of the electrodes in order to determine the best option for fabricating the solar cells presented in section Indium-doped tin oxide (ITO)-Free Perovskite Solar Cells Based on SnO2/Au/SnO2 and MoOx/Au/SnO2 Electrodes

Summary

Introduction

Organic-inorganic perovskite solar cells (PSC) are on the rise as the most promising contenders among new generation photovoltaic technologies, due to the outstanding optoelectronic properties of perovskite absorbers (Correa-Baena et al, 2017) as well as associated low-cost and compatibility with large area fabrication processes (Razza et al, 2016). The efficiency achieved for flexible PSCs still lacks behind their rigid counterparts, with a record of 18.4% (Feng et al, 2018). This is due to the stringent process limitations imposed by plastic substrates, which suffer irreversible degradation at temperatures above 150◦C (Zardetto et al, 2011), to the different wetting/growth of the perovskite active layer on flexible films (Bi C. et al, 2017), and to the generally inferior compromise between transmittance and conductance of transparent electrodes on plastic (Heo et al, 2019)

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