Low-temperature crystallization of solution-derived metal oxide thin films assisted by chemical processes

The versatility of wet chemical methods allows the easy exploration of novel crystallization pathways for metal oxides thin films and makes them fundamental in the search of low-temperature methods. The benefits obtained from... [ view full abstract ]

The versatility of wet chemical methods allows the easy exploration of novel crystallization pathways for metal oxides thin films and makes them fundamental in the search of low-temperature methods. The benefits obtained from decreasing the processing temperature span from minimizing the environmental impact (carbon footprint) to reducing the overall costs of the production line. More challenging is the preparation of crystalline complex oxide films at temperatures compatible with their direct integration in flexible substrates (≤350 ºC). However, the high crystallization temperatures of these materials, usually over 600 ºC, impede the development of devices that take full advantage of the large variety of oxide functionalities available. This work summarizes a number of strategies based on wet chemical methods for inducing the crystallization of metal oxide thin films at low temperatures.¹ The key mechanisms are explained in relation to the specific step of the fabrication process reached in an earlier stage: the formation of a defect-free, highly densified amorphous metal–oxygen network or the actual crystallization of the metal oxide. The role of photochemistry, where light can be used as a complementary energy source to induce crystallization, is particularly highlighted. This requires the synthesis of photosensitive precursor solutions (modified metal alkoxides, charge-transfer metal complexes or structurally designed molecular compounds) and a precise control over the reactions promoted by UV irradiation (photochemical cleavage, ozonolysis, condensation or photocatalysis). Relevant examples derived from the integration of crystalline metal oxide thin films (photoferroic BiFeO₃, ferroelectric Pb(Zr,Ti)O₃ or photocatalytic β-Bi₂O₃) on flexible substrates (≤350 ºC) will illustrate the most recent achievements in this field by our group.^2,3

[1] Bretos et al., Chem. Soc. Rev., 2018, 47, 291-308.

[2] Bretos et al., Adv. Mater., 2015, 27, 2608-2613.

[3] Bretos et al., Adv. Mater., 2014, 26, 1405-1409.

 Supported by Spanish Project MAT2016-76851-R and Fundación General CSIC (ComFuturo Programme).