Copper (I) Selenocyanate (CuSeCN) as a Novel Hole‐Transport Layer for Transistors, Organic Solar Cells, and Light‐Emitting Diodes

Abstract

The synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution-processable hole-transport layer (HTL) material in transistors, organic light-emitting diodes, and solar cells are reported. Density-functional theory calculations combined with X-ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution-processed layers are found to be nanocrystalline and optically transparent (>94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at −5.1 eV. Hole-transport analysis performed using field-effect measurements confirms the p-type character of CuSeCN yielding a hole mobility of 0.002 cm 2 V −1 s −1 . When CuSeCN is incorporated as the HTL material in organic light-emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4-ethy lenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides.

Taming Copper(I) Cyanate and Selenocyanate with N‐Heterocyclic Carbenes

“…Within the reported structures, the selenocyanate ligand, is commonly observed to coordinate in a bridging µ‐1,3‐NCSe mode (see Scheme ) between the copper(I) centres. More recently, copper(I) selenocyanate has been shown to have potential as a p‐type semiconductor, therefore raising the profile of this species and related adducts …”

Copper Thiocyanate and Copper Selenocyanate Hole Transport Layers: Determination of Band Offsets with Silicon and Hybrid Perovskites from First Principles

“…As expected, the size of the bandgap is underestimated as compared with the experimental value of 3.60 eV but in agreement with a previously reported theoretical value of 2.17 eV . On the other hand, CuSeCN has a direct bandgap of 1.81 eV (at the Γ point), which is smaller than the experimental value of 3.53 eV but in agreement with a previously reported theoretical value of 1.71 eV . The partial densities of states in Figure indicate a dominating Cu 3 d character at the valence band maximum, whereas the C 2 p and N 2 p states dominate at the conduction band minimum.…”

“…CuSeCN is a chemically stable p‐type semiconductor, structurally similar to CuSCN. Wijeyasinghe et al recently developed solution‐processable thin films and fabricated thin‐film transistors (TFTs), organic photovoltaics (OPVs), and organic light emitting diodes (OLEDs) to demonstrate its potential in microelectronics and optoelectronics . Both CuSCN and CuSeCN have enhanced hole transport characteristics attributed to the Cu vacancies that move the Fermi level into the valence band close to its maximum …”

“…CuSCN and CuSeCN have been reported experimentally in both orthorhombic (α) and hexagonal (β) phases; the latter phase being energetically favorable by 52 and 34 meV per formula unit, respectively. Therefore, we consider the β‐phase with space group P6 3 mc.…”

“…Figure shows the resulting level alignment diagrams, and Table lists the calculated values of Δ E v together with the final results for the VBO and CBO. The CBOs are calculated using bandgaps of 3.60 eV (CuSCN), 3.53 eV (CuSeCN), 1.10 eV (Si), 1.50 eV (MAPbI 3 ), 2.34 eV (MAPbBr 3 ), and 2.26 eV (FAPbBr 3 ). We observe that the VBOs are smaller for CuSCN than for CuSeCN, suggesting that CuSCN is superior as a hole transport layer.…”