Cuprous iodide - a p-type transparent semiconductor: history and novel applications (Phys. Status Solidi A 9∕2013)

Abstract

Cuprous iodide has been investigated since 1907 when Karl Bädeker prepared this material from metallic copper thin films with subsequent iodization and reported it as fully transparent conductor. Nowadays CuI is recognized as p‐type wide bandgap, transparent semiconductor, offering rather high hole mobilities of so far up to 10 Vs∕cm2 in thin films. The charge carrier density is primarily controlled via the amount of copper vacancies. CuI has been prepared as bulk material and substrate and thin film as well as in the form of various nanostructures. Thin films can be prepared by various techniques including iodization of copper and by thermal evaporation, sputtering or pulsed laser deposition of CuI. Recent progress is represented by the epitaxy on other semiconductors, in particular zinc oxide. CuI has found use as intermediate layer between ITO and organic absorbers in solar cells. Recently, bipolar heterostructure diodes prepared from p‐CuI∕n‐ZnO layers on sapphire were found to exhibit very high rectification. This makes CuI interesting for use in transparent electronics. For further details see the Review Article by M. Grundmann et al. on pp. http://doi.wiley.com/10.1002/pssa.201329349.

Electronic Properties of Copper(I) Thiocyanate (CuSCN)

“…[62] It is also noteworthy to acknowledge copper iodide (CuI) as it is a well-known p-type metal halide also based on Cu(I) and has been employed in several device applications as a hole-transporting layer. [63][64][65][66] Although the conductivity of γ-CuI is electronic, α-CuI and β-CuI also show strong ionic conductivity [67] and may present a challenge in the development of electronic devices. However, a full discussion on CuI is beyond the scope of this work as it is a common metal halide and does not possess the quasi-molecular nature as in the case of pseudohalides.…”

“…However, a full discussion on CuI is beyond the scope of this work as it is a common metal halide and does not possess the quasi-molecular nature as in the case of pseudohalides. To this end, Grundmann et al [67] have recently published a comprehensive review of the properties and applications of CuI.…”

Efficient organic solar cells using copper(I) iodide (CuI) hole transport layers

“…13 In an effort to address some/all of these issues, a range of alternative HTL materials have been investigated, including PSS-free vapor phase polymerized PEDOT, 14,15 graphene oxide, 16 22 It exhibits three crystalline phases, namely, a, b, and c, 23 of which the c-CuI zinc blende structure (cubic), known to form at deposition temperatures below 390 C, is the most interesting for our purpose. c-CuI is a ptype, wide-bandgap ($3.1 eV) 24 semiconductor and, due to its optical transparency and favourable Fermi level energy, has previously been used as a HTL in solid-state dye-sensitized solar cells. 25 CuI has also been incorporated in organic light emitting diodes (OLEDs) 26 and organic solar cells.…”

“…Furthermore, XRD analysis revealed that both samples exhibit exclusively (111) and (222) peaks, consistent with a dominant c-CuI zinc blende structure. 24 CuI(eva) films appear, however, to be composed of larger crystallites than CuI(sln) layers (Table S1). 31 Again, this difference may be responsible for the stoichiometric, and hence electronic, differences between the two types of CuI layers.…”

“…Both CuI layers exhibit an absorption onset at $420 nm (2.95 eV), with a sharp peak for CuI(sln) and a shoulder for CuI(eva) at $404 nm (3.07 eV) that can be assigned to the Z 1,2 band edge exciton transitions. 24 The higher energy peak at $336 nm (3.69 eV) is then the associated Z 3 split-off band transition and that at $258 nm (4.80 eV) the E 1 transition from the top valence band to the conduction band at higher k along the [111] direction. 24 Additional features appear near 371 nm and 381 nm for CuI(eva) and may, in part, arise from the effects of strain 24 but further studies will be needed to confirm or refute this proposal.…”