Chemical Synthesis of La_0.75Sr_0.25CrO₃ Thin Films for p-Type Transparent Conducting Electrodes

Abstract

The imperative need for highly performant and stable p-type transparent electrodes based on abundant metals is stimulating the research on perovskite oxide thin films. Moreover, exploring the preparation of these materials with the use of cost-efficient and scalable solution-based techniques is a promising approach to extract their full potential. Herein, we present the design of a chemical route, based on metal nitrate precursors, for the preparation of pure phase La0.75Sr0.25CrO3 (LSCO) thin films to be used as a p-type transparent conductive electrode. Different solution chemistries have been evaluated to ultimately obtain dense, epitaxial, and almost relaxed LSCO films. Optical characterization of the optimized LSCO films reveals promising high transparency with ∼67% transmittance while room temperature resistivity values are 1.4 Ω·cm. It is suggested that the presence of structural defects, i.e., antiphase boundaries and misfit dislocations, affects the electrical behavior of LSCO films. Monochromated electron energy loss spectroscopy allowed changes in the electronic structure in LSCO films to be determined, revealing the creation of Cr4+ and unoccupied states at the O 2p upon Sr-doping. This work offers a new venue to prepare and further investigate cost-effective functional perovskite oxides with potential to be used as p-type transparent conducting electrodes and be easily integrated in many oxide heterostructures.

Unfolding the Challenges To Prepare Single Crystalline Complex Oxide Membranes by Solution Processing

“…In addition, from the strain maps in Figure d, it is observed that the BFO film exhibits inhomogeneous lattice deformations likely due to the numerous nucleation of structural defects that locally relax the BFO lattice. In fact, CSD tends to promote the formation of structural defects within the epitaxial thin film, as previously reported in other complex oxides. ,, A more detailed analysis of these local deformations in the BFO layer by means of atomically resolved STEM images is presented in Figure S4.…”

“…Further XRD structural analysis from this heterostructure identifies that the LSMO film is partially strained (+0.3%), whereas the BFO is fully relaxed with a = 3.96 Å, matching the bulk value . This is not surprising considering that CSD films with similar thickness tend to grow fully relaxed through the formation of structural defects. , Cross-section STEM reveals the growth of three discrete layers in which BFO presents few Fe-rich secondary phases, ,, Figure b. Image magnification at the BFO/LSMO interface shows the atomic structure of both phases, corroborating their epitaxial relationship with an atomically sharp interface, Figure c.…”

“…38 This is not surprising considering that CSD films with similar thickness tend to grow fully relaxed through the formation of structural defects. 30,39 Cross-section STEM reveals the growth of three discrete layers in which BFO presents few Fe-rich secondary phases, 30,33,40 phases, corroborating their epitaxial relationship with an atomically sharp interface, Figure 3c. Unlike the previous scenarios, here EELS elemental mapping confirms the absence of both cation interdiffusion and Fe migration to the sacrificial layer; see Figure 3d.…”

“…In fact, CSD tends to promote the formation of structural defects within the epitaxial thin film, as previously reported in other complex oxides. 39,43,44 A more detailed analysis of these local deformations in the BFO layer by means of atomically resolved STEM images is presented in Figure S4.…”

Chemical synthesis of complex oxide thin films and freestanding membranes

“…We performed a thorough study on the influence of the solution chemistry based on metal nitrates to ultimately obtain epitaxial and reasonably smooth films on (001) STO and (001) LaAlO 3 (LAO) substrates. 93 The optimal formulation appeared to be nitrate precursors in 2-methoxyethanol, acetic acid and diethanolamine, processed in air which results in dense, epitaxial and slightly strained films. These LSCO films display 67% optical transparency in the visible spectrum being as good as those reported for some of the most promising state of the art TCOs.…”