Oxygen‐Induced Phase Separation in Sputtered Cu–Sn–I–O Thin Films

Abstract

Transparent amorphous semiconductors have been intensively investigated in recent years as they are of interest for a wide range of applications, in particular for flexible electronics such as solar cells or transparent displays. In contrast to their crystalline counterparts, amorphous semiconductors exhibit a superior morphology, namely being smoother, denser, and free of grain boundaries. Additionally, they can be fabricated at low temperatures on a variety of substrates including plastic. [1,2] Suitable n-type transparent amorphous semiconductors, like In-Ga-Zn-O, have been readily available for some years. [1][2][3] However, well-performing p-type transparent amorphous semiconductors are still lacking. Promising candidates to fill this serious gap are Cu-Sn-I thin films, which combine optical transparency with high p-type conductivity. Indeed, it is reported that they possess hole densities and Hall mobilities comparable to those of polycrystalline CuI. [4] Amorphous Cu-Sn-I thin films with a Sn content of 10%-15% with respect to the metal fraction, that is, with Sn/(Cu þ Sn) ¼ 0.10-0.15, were successfully deposited on glass substrates or polymer foils by spin-coating of a CuI-SnI 4 precursor solution. [4,5] Based on these findings, theoretical studies have calculated the structural and electrical properties of Sn-doped amorphous CuI by density-functional theory and ab initio

Cs‐Doped and Cs‐S Co‐Doped CuI p‐Type Transparent Semiconductors with Enhanced Conductivity

“…The XANES is identical for both TCs and reveals no signs of oxidation of Cu (Figure 1E). [34] If we look at the Fourier transform of the extended EXAFS (Figure 1F), we see again the same features with nearly identical amplitudes for both films. This demonstrates that the local coordination of Cu in the HD-Cs:CuI film is the same as in intrinsic CuI.…”

“…The fit quality is excellent and we obtain d = (2.607 ± 0.001) Å and σ 2 = (2.1 ± 0.1) x 10 −3 Å 2 for intrinsic CuI, in good agreement with previous reports. [ 34,35 ] The average Cu‐I bond length and bond length disorder obtained for the HD‐Cs:CuI are identical to those of intrinsic CuI within the given uncertainty. This confirms that the average local structure surrounding Cu is the same for both TCs and that the crystalline quality on the sub‐nanometer scale is not diminished by incorporation of up to ≈4 at.…”

“…The coordination number was set to the zincblende value of 4 since the XANES spectra showed no signs of oxidation. [ 34 ] The same amplitude reduction factor and threshold energy were used for both films. Note that fluorescence XAS measurements at the Cs L‐edges (5.0–5.8 keV) were not feasible due to the strong overlap with the simultaneously excited iodine fluorescence lines whereas measurements at the Cs K‐edge (35.985 keV) were impractical for thin films due to the extremely low absorption at such high X‐ray energies.…”