Ultrafast and Scalable Laser‐Induced Crystallization of Titanium Dioxide Films for Planar Perovskite Solar Cells

Abstract

TiO 2 has been recognized as a promising material for a wide range of emerging applications, including hydrogen generation, [1] CO 2 reduction, [2] degradation of organic pollutants, [3] self-cleaning coating, [4] quantum-dot-sensitized solar cells, [5] dyesensitized solar cells (DSSCs), [6] and more recently perovskite solar cells (PSCs). [7,8] Thermal annealing is a critical process involved in the fabrication of TiO 2 films for PSCs. For instance, a compact TiO 2 film that acts as an electron transport layer (ETL) for PSCs usually requires an annealing temperature of over 400 C to induce the crystallization from its amorphous precursor to anatase. [9,10] The fabrication of the mesoporous TiO 2 film for mesoscopic PSCs also needs high-temperature sintering of around 450-550 C to remove organic binders from TiO 2 paste and promote the interconnection between the TiO 2 nanoparticles. [11,12] A typical conventional annealing method is a time-consuming batch process involving the uses of a hotplate, furnace, or oven, for 1-3 h to fabricate these layers, including a long cooling period. [12-14] Such a process makes it challenging to develop high throughput or in-line production of PSCs. Therefore, there is a need to develop an alternative annealing method, enabling the rapid and scalable production of high-quality metal oxide films for PSCs for future commercialization. In addition, conventional annealing methods are commonly limited to below 550 C to avoid glass substrate bending or breakage due to a glass transition temperature of 564 C for substrate based on soda-lime glass. [15] Previous studies have suggested that an annealing temperature beyond 600 C enhances the crystallinity of the TiO 2 films and interconnection between the nanoparticles, which improves the performance of the PSCs and other devices. [13,16-18] To date, several alternative annealing methods have been developed to fabricate TiO 2 ETL for PSCs and DSSCs. For instance, Watson et al. demonstrated the use of an ultrafast near-IR (NIR) heating process to sinter mesoporous TiO 2 film on metal substrates for DSSCs. [19] Sánchez et al. developed a rapid flash IR method to anneal mesoporous TiO 2 film for PSCs with a peak temperature of %640 C and achieved a production rate of 15 cm 2 min À1 (1 cm 2 in 4 s). [11] Kim et al. demonstrated a flame annealing process to anneal the TiO 2 film for PSCs and DSSCs with a peak temperature up to 1000 C and

Laser-Assisted Ultrafast Fabrication of Crystalline Ta-Doped TiO2 for High-Humidity-Processed Perovskite Solar Cells

“…This is possibly due to a more efficient oxidation of the Ta-TiO 2 in ambient air with the high-temperature laser treatment as well as a more effective removal of the organic residues from the Ta-TiO 2 precursor. 49 , 50 Previous studies suggested that the Ti 3+ defects acting as the defects at the surface of TiO 2 hinder the electron transport and increase the chances of charge recombination, thus leading to a reduced photovoltaic performance of the PSCs. 51 , 52 Therefore, a lower concentration of Ti 3+ defects on the surface of Ta-TiO 2 treated with peak laser processing temperatures of 800–850 and 900–950 °C might contribute to a better device performance in comparison to the furnace-treated Ta-TiO 2 .…”

“…The compact TiO 2 layers were fabricated in the same way as in our previous method. 49 The substrate was then annealed at 500 °C for 30 min in a furnace and finally cooled for 3 h to complete the furnace process. For Ta-doped solar cells, a certain amount of tantalum(V) butoxide was added to the TiO 2 precursor with different molar ratios of Ta/Ti (1.0, 3.0, and 5.0 mol %).…”

Laser Processing Methods for Perovskite Solar Cells and Modules

“…[ 85 ] In a follow‐up work, Chen demonstrated the simultaneous laser annealing of stacked dense plus mesoporous ETL layers. [ 86 ] For the dense TiO 2 layers, surface temperatures of up to 850 °C and annealing times as low as 18.5 s yielded highly crystalline TiO 2 . The underlying ITO TCO was observed to exhibit a significantly lower increase in resistance when compared to the commonly used 500 °C, 30 min hot plate annealing.…”

“…An improved PV performance and significant reduction in processing time indicates a potential path forward for the production of large surface area devices. Figure 13 [ 86 ] illustrates the scalable laser process compared to a conventional furnace annealing for crystallization of TiO 2 ETLs.…”

A Multi-Electron Transporting Layer for Efficient Perovskite Solar Cells

“…Typically, the structure of a perovskite solar cell mainly consists of three parts: an electron transporting layer (ETL), a perovskite layer, and a hole transporting layer (HTL). Recently, metal oxide wide-band-gap semiconductors such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), etc., have gained attraction for PSC applications as the charge transporting layer [9][10][11][12][13][14]. This is because of their high mobility, good energy alignment, and use of low-temperature processes [15][16][17].…”