Alternative Electron Transport Layer Based on Al-Doped ZnO and SnO₂ for Perovskite Solar Cells: Impact on Microstructure and Stability

Abstract

The stability of perovskite solar cells (PSCs) is currently a hot topic, but the investigation as well as the understanding of the degradation mechanisms remain incomplete. We present the intrinsic degradation mechanisms of a traditional monocation perovskite in photovoltaic devices performed with various electron transport layers (ETLs). The monocation perovskite material is a Cl-doped CH 3 NH 3 PbI 3 system, known to provide a favorable morphology leading to improved efficiency. With the long-term view of developing low-temperature processes for PSCs, two emerging ETLs compatible with TiO 2 substitution were chosen in order to study both the initial perovskite state and performance, along with their stability after aging. Aluminumdoped zinc oxide (AZO) and tin oxide (SnO 2 ) were thus selected and placed as the ETL in a planar NIP solar cell architecture, leading to different n-type substrates that can imply deviations in the formation and/or degradation of the perovskite layer. As a result, the overall performance and stability for the designed devices were strongly impacted using AZO as compared to SnO 2 . A detailed investigation using complementary characterization techniques helped in the understanding of the initial compositions and morphologies of the perovskite according to the underlying ETL layer used and their unalike evolution during mild aging conditions (inert atmosphere, dark, 35 °C). Infrared spectroscopy, X-ray diffraction, UV−visible absorption, photoluminescence, scanning electron microscopy, and current−voltage characteristics brought a new understanding of the local degradation mechanisms and their consequences on the macroscopic functional properties of PSC devices. Two different degradation mechanisms specific to the ETL have been distinguished. The ETL nature controls the perovskite microstructure and thereby the performance and stability of the complete device.

A Comparison of the Structure and Properties of Opaque and Semi-Transparent NIP/PIN-Type Scalable Perovskite Solar Cells

“…As a result, very similar optical bandgaps at 1.62 eV were obtained by the Tauc plot method (Figure S3 and Table S1). These are a bit larger than the values reported for MAPbI 3 [13] but closer to the ones related to chlorine-doped perovskite [43,45,53]. However, using the same deposition protocol, the perovskite layer deposited on PTAA is found to be thicker than that deposited on np-SnO 2 (280 nm against 225 nm as determined experimentally with a profilometer).…”

“…The sharp absorption onset may be varied with the chemistry and processing conditions to tune the perovskite's bandgap within a wide range from 1.17 to 3.11 eV [11][12][13][14][15]. As a result, perovskite materials have garnered great interest for tandem applications [16,17], especially with silicon cells [18][19][20][21][22], the main Tin oxide nanoparticles (np-SnO2) and poly-triarylamine polymer (PTAA) were selected for their reported compatibilities with the perovskite interface, leading to efficient PSCs [19,20,[40][41][42][43]. These materials are well-suited for low temperature processes and, thereby, for a tandem application with silicon heterojunction cells.…”

“…Tin oxide nanoparticles (np-SnO 2 ) and poly-triarylamine polymer (PTAA) were selected for their reported compatibilities with the perovskite interface, leading to efficient PSCs [19,20,[40][41][42][43]. These materials are well-suited for low temperature processes and, thereby, for a tandem application with silicon heterojunction cells.…”

Influence of Chloride/Iodide Ratio in MAPbI3-xClx Perovskite Solar Devices: Case of Low Temperature Processable AZO Sub-Layer

“…Moreover, TiO 2 based devices are known to suffer from critical deterioration under ultraviolet illumination. Several studies have already been conducted with other metal oxides compatible with low temperature processes, specifically ZnO [9,10] and SnO 2 [11,12]. SnO 2 demonstrated a great transmission rate and an elevated electron mobility, with adapted energy band gap and relatively deep conduction band level.…”

Effect of Source-Substrate Distance on Transparent Electrode Properties of the Spray-Cast Aluminium Doped Zinc Oxide Thin Films

“…have been realized. Especially, AZO films have comparable optoelectronic properties as that of widely used TiO2 layer which suffers from degradation under UV-irradiation and low electron mobilities [10,11].…”