Origin of Hole‐Trapping States in Solution‐Processed Copper(I) Thiocyanate and Defect‐Healing by I₂ Doping

Abstract

Solution‐processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short‐range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X‐ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide‐based recipe is found to contain under‐coordinated Cu atoms, pointing to the presence of SCN− vacancies. A defect passivation strategy is introduced by adding solid I2 to the processing solution. At small concentrations, the iodine is found to exist as I− which can substitute for the missing SCN− ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I2‐doped CuSCN as a p‐channel in thin‐film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I2 doping method leads to the defect‐healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance‐voltage characteristics corroborates that the trap state density is reduced upon I2 addition.

Engineering High-k Oxide/CuSCN Interface for p-Channel Thin-Film Transistors

“…The XRD results are shown in Figure d. All CuSCN films could be identified as the 3R β-CuSCN phase with diffractions at 2θ = 16.2, 27.3, and 47.2° associated with (0 0 6), (1 0 ), and (2 0) planes . We can observe that the THF treatment increased the orientation of the (0 0 6) direction (crystallographic c -axis).…”

“…CuSCN is unique as it belongs to the family of coordination polymers, for which practical device applications have only begun to appear despite the large material library and structural versatility . Specifically for CuSCN-based TFTs, following the first demonstrations of p-channel transistors and logic circuits, , recent advances have been made on the doping, , fine-tuning the microstructures, and defect healing . These studies yield important insights into the processing of the semiconducting CuSCN layer, which can improve the hole-transport properties.…”

Contrasting analog and digital resistive switching memory characteristics in solution-processed copper(i) thiocyanate and its polymer electrolyte-based memristive devices

“…Above 350 nm (mainly in the visible region), no significant absorption is observed for the powder CuSCN, while the thin film of CuSCN shows some absorption in the visible region that may be due to the defects or trap states created in the film. 35 The absorption spectra of the CuSCN powder and the thin film show a peak at B297 nm, a characteristic of CuSCN. 35 The optical band gap energy was calculated from the Tauc plot, as shown in the inset of Fig.…”

“…35 The absorption spectra of the CuSCN powder and the thin film show a peak at B297 nm, a characteristic of CuSCN. 35 The optical band gap energy was calculated from the Tauc plot, as shown in the inset of Fig. 1b.…”

Band gap engineering in pyridyl-functionalized two-dimensional (2D) CuSCN coordination polymers

“…Recently, the importance of coordination chemistry in CuSCN has been realized, leading to a deeper understanding of its structureproperty relationships and novel strategies to improve the performance of CuSCN-based devices, such as by antisolvent treatment or SCN − defect passivation. [16][17][18] CuSCN is in fact a 3D coordination polymer (CP) consisting of Cu(I), a soft acceptor, tetrahedrally linked by the bidentate SCN − , which is a soft donor. 19 Its structure thus allows for a diverse range of structural modifications via ligand (L) engineering.…”