Impact of Conformality and Crystallinity for Ultrathin 4 nm Compact TiO₂ Layers in Perovskite Solar Cells

Abstract

The rapid rise in power conversion efficiencies of lead-based perovskite solar cells (PSCs) has established their promise, motivating scale-up and commercialization. As a thin film solar cell, interfacial properties are key to the performance of PSCs; there is a need to further understand which properties are critical to control. In this work, the impact of the compact TiO 2 (com-TiO 2 ) film properties on the performance of mesoporous PSCs is studied. Com-TiO 2 layers are fabricated by spray pyrolysis as well as by atomic layer deposition (ALD), using ALD as a proof-of-concept method to achieve highly conformal films of precisely controlled thickness. The com-TiO 2 layers' conformality and surface roughness are examined by microscopy techniques; their relative crystallinity is studied by grazing-incidence X-ray diffraction with a synchrotron source and an in situ annealing chamber; and completed devices are analyzed by J-V and impedance spectroscopy techniques. The results show that an ultraconformal com-TiO 2 layer can be thinned to 4 nm and match the performance of a ≈50 nm spray-pyrolysis TiO 2 layer. This work concludes that film conformality is the primary consideration for creating a high-performing com-TiO 2 layer, overriding any effects of film crystallinity-a finding that can guide fabrication choices for the scale-up of PSCs.

Highly Efficient Photoelectrochemical and Photocatalytic Anodic TiO2 Nanotube Layers with Additional TiO2 coating

“…It was already demonstrated on photocurrent, XPS and other investigations in the previous literature that ALD TiO 2 nanolayers are of very high quality compared to other TiO 2 nanostructures [33,40,41].…”

Electrodeposition of SnO2 on FTO and its Application in Planar Heterojunction Perovskite Solar Cells as an Electron Transport Layer

“…The SnO 2 film morphology is expected to significantly affect the PSC performance because planar PSCs have a direct interface between the ETL and the perovskite layer. The improved conformality could result in good contact that affords enhanced electron transport [ 25 ]. The SEM images of perovskite layer fabricated from varied ETLs were provided in supporting information (SI) Additional file 1 : Figure S1.…”

Emerging Organic/Hybrid Photovoltaic Cells for Indoor Applications: Recent Advances and Perspectives

“…Recently, the highly dense TiO 2 layer was observed to have a positive impact on effectively blocking the migration of holes in perovskite under an indoor light environment and preventing direct contact between the perovskite layer and the electrode, which resulted in a higher efficiency. [ 77 ] Different methods were investigated for TiO 2 film preparation, such as low‐temperature atomic layer deposition (LT‐ALD), [ 78 ] application of high‐temperature sol–gel (SG) coatings, [ 79 ] and deposition through high‐temperature spray pyrolysis (SP). [ 80 ] Di Giacomo et al utilized these three methods to explore the influence of film preparation methods on the performance of perovskite‐based indoor photovoltaics [11f] .…”

“…Consequently, higher PCEs were achieved in the ALD-based cells (an average PCE of 20.9%) when compared with the other two types of devices (an average PCE of 0.1% and 4.8% for the SP-and SG-based cells, respectively) under 200 lx. This occurrence was because the compact TiO 2 created by ALD had a smaller pinhole density, [64,78,81] which prevented the recombination between the perovskite layer and the transparent conducting oxide. Moreover, the SEM image showed that the LT-ALD TiO 2 induced a small crystal overlay on top of the perovskite film, thereby preventing direct contact between the TiO 2 and the hole translate materials (Spiro-OMeTAD), thereby reducing the additional recombination pathways.…”