TiO₂ Colloid‐Spray Coated Electron‐Transporting Layers for Efficient Perovskite Solar Cells

Abstract

it provides a larger contact area between the TiO 2 and perovskite. Almost all of the best PSC efficiencies published so far have been obtained by using TiO 2 photoelectrodes. [15-18] Moreover, excellent long-term photo-stability has also been reported in PSCs fabricated using TiO 2 electrodes. [19] mp-TiO 2 layers for PSCs can be formed using spin-coating or screen-printing methods with TiO 2 pastes containing organic binders and surfactants (e.g., ethyl cellulose and terpineol), as well as organic solvents. [20,21] Subsequently, the TiO 2 layers require a follow-up such as high-temperature process to burn out the organic components contained in the TiO 2 paste. The biggest advantage of a hightemperature process would be a lowering of the series resistance of the layer, due to the strong contact between the TiO 2 particles and the TCO substrate. Therefore, in terms of efficiency, high-temperature-processed TiO 2 layers are very desirable; nevertheless, their use may be a large limiting factor in the fabrication of PSCs using a low-temperature continuous coating process or substrates based on an organic material (e.g., polyethylene naphthalate (PEN)). [22] Even PEN-based flexible substrates can be problematic, because they can bend if subjected to a heat treatment at 150 °C. Although recent studies have shown that SnO 2 can be used as an ETLs to fabricate PSCs at relatively low temperature, a heat treatment at temperature ≥150 °C is required to reach the best performances. [23,24] Meanwhile, formamidinium lead triiodide (FAPbI 3)-based perovskites are generally heat-treated at 150 °C to obtain an α-phase. If all the processes for high-efficiency PSCs can be conducted at ≈100 °C, their value will be very high in terms of using flexible substrates and facilitating large-area continuous processes. Currently, most high-efficiency PSCs are fabricated using spin coating, a simple and reliable technique that can produce very uniform thin films. However, since it is problematic to apply spin coating in large-area processes, other methods including blade coating, [25] slot die coating, [26] inkjet printing, [27] and spray coating [28] have been actively studied as scalable deposition techniques. Among these, spray coating has been already widely used in several industry fields and offers great advantages for the continuous production of PSC modules with large areas and a reduced material consumption. [29] So far, several groups reported the deposition of perovskite thin films or of entire ETLs, perovskites, and HTLs (required for the fabrication TiO 2 is one of the most efficient and widely used materials for electrontransporting layer (ETLs) in perovskite solar cells (PSCs). The formation of efficient TiO 2 layers is generally carried out at high temperature by baking at a temperature >400 °C or by vacuum deposition (e.g., atomic layer deposition and E-beam). In this study, the preparation of a TiO 2 ETL for PSCs is reported with excellent properties at low temperatures based on the synthesis of a stable TiO 2 colloidal ...

Recent Developments in Upscalable Printing Techniques for Perovskite Solar Cells

“…They achieved a PCE of 17.8% and 16.6% for the module sizes of 6 × 6 cm 2 and 10 × 10 cm 2 , respectively. [131] In addition, spray-coating of SnO 2 , [160,161] TiO 2 , [162,163] NiO x [164,165] and carbon electrode [166] has been recently reported. Besides the significant development of the spray coating process, a maximum PCE of 19.4% has been obtained by a fully spray-Figure 6.…”

Improvement of Thiourea (Lewis Base)-Modified SnO2 Electron-Transport Layer for Carbon-Based CsPbIBr2 Perovskite Solar Cells

“…In previous studies, the morphology of the electron-transport layer (ETL) had a significant influence on the morphology of the perovskite layer. 15,43,45 The morphology of the SnO 2 films modified with different concentrations of thiourea is shown in Figure 1. It can be seen that the surface of SnO 2 became slightly smooth with the increase in thiourea concentration.…”

“…However, due to the easy decomposition and aging of its organic components, the stability of the PSCs in high-humidity, high-oxygen, and high-temperature environments still needs to be improved. − In addition, the high cost and instability of organic electron–hole-transport materials have also become the stumbling blocks to the commercialization of PSCs . To improve the stability and reduce the cost of PSCs, the preparation of an electron–hole-transport layer of the PSCs using inorganic materials has become a new research hotspot. − …”

A “double-sided tape” modifier bridging the TiO2/perovskite buried interface for efficient and stable all-inorganic perovskite solar cells

“…28 The successful instances described above strongly suggest that the interface engineering with multifunctional modiers at the TiO 2 /perovskite buried interface is viable and efficient for further improving the PCE of PSCs. [29][30][31] Herein, a common and stable inorganic ammonium salt of diammonium hydrogen phosphate (DAP) with the advantages including cost effectiveness, easy preparation and low toxicity, containing positive and negative ions in contrast with Lewis base or acid that endows it with the function of simultaneous reactions with anions and cations is exploited as a "doublesided tape" modier to be deposited at the TiO 2 /perovskite buried interface to effectively improve the PSC performance. The modication of DAP can concurrently passivate the interfacial defects and modulate the interface contact and energy level matching as well as perovskite growth.…”