Enhanced p‐Type Transparent Semiconducting Characteristics for ALD‐Grown Mg‐Substituted CuCrO₂ Thin Films

Abstract

Magnesium‐substituted CuCrO2 delafossite is a promising candidate for p‐type transparent conducting oxide applications owing to its relatively high electrical conductivity and optical transparency in the visible range. Here, the atomic layer deposition fabrication of semiconducting Cu(Cr1−xMgx)O2 (up to x = 0.043) thin films based on Cu(thd)2 (thd = 2,2,6,6‐tetramethyl‐3,5‐heptanedionate), Cr(acac)3 (acac = acetyl acetonate), and Mg(thd)2 as metal precursors and ozone as the oxygen source is reported. Smooth and homogeneous thin films with an accurately controlled Mg content are obtained at the deposition temperature of 250 °C. A limited substitution level is revealed from X‐diffraction patterns: peaks due to the spinel‐structured MgCr2O4 secondary phase appear for x ≥ 0.015 while the increase in lattice parameters of the delafossite Cu(Cr,Mg)O2 phase continues even up to x ≈ 0.03. The direct bandgap as determined from UV–vis spectrophotometric measurements is observed to decrease from 3.09 eV for x = 0 to 2.87 eV for x = 0.015 before increasing to 3.15 eV for x = 0.043. The observed transmittance is close to 80% in the visible range. These characteristics are superior to the thin films of the copper delafossite family prepared by any thin‐film technique.

Atomic Layer Deposition of p‐Type Semiconducting Thin Films: a Review

“…Transm ittance spe ctra for the Cu(Cr1−xMgx)O2 films; the inset shows the room-temperature electrical conuctivity values with increasing Mg content x. [192] Other recent results are for CuO films for which the electrical resistivity and Seebeck coefficient follow conventional semiconducting behavior, but an anomalous dependence of the optical bandgap on the film thickness was revealed. Generally, inverse-square-root dependence of the optical bandgap on the film thickness is expected, but for the ultrathin ALD CuO films a proportionalcubic-root dependence was observed.…”

“…The low deposition temperature is beneficial also for avoiding the native vacancy/interstitial defects in p-type oxides thus promoting the enhanced electrical and optical properties of these materials, as was the case for example with the p-type delafossite Cu(Cr,Mg)O2 thin films; here the electrical and optical functionalities were strongly enhanced for the ALD-fabricated films compared to the films prepared by conventional deposition techniques. [192] With the ever decreasing scale of many novel applications, the high degree of conformality that can be achieved with ALD will further increase the importance of the technology in the coming years.…”

“…Particularly promising characteristics were recently realized for the delafossite-structured CuCrO2 and its Mg-doped derivative. [192,194] For the latter Cu(Cr,Mg)O2 system, record-high p-type electrical conductivity (220 S cm -1 ) values -among the delafossite family -had been previously reported for thin films fabricated by PLD, but the transmittance values for these films in the visible range were as low as ~40%. [34] Most importantly, for the ALD-fabricated Cu(Cr,Mg)O2 films the high electrical conductivity value (217 S cm -1 ) was accompanied with the high optical transparency of ~80% ( Figure 5).…”

“…However, very recently promising results were obtained even for the quaternary Cu(Cr,Mg)O2 system. [192] The ALD process is based on Cu(thd)2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate), Cr(acac)3 (acac = acetyl acetonate) and Mg(thd)2 as metal precursors and ozone as the oxygen source. Smooth and homogeneous thin films with an accurately controlled Mg content were obtained at the deposition temperature of 250 o C. In the deposition super-cycle, n*[(Cu(thd)2+O3) + 3*(Cr(acac)3+O3)] + [(Cu(thd)2+O3) + 2*(Cr(acac)3+O3) + (Mg(thd)2+O3)], the Mg-doping level could be accurately controlled by the choice of n up to a few mol-% substitution levels (down to n ≈ 10).…”

Hole‐Boosted Cu(Cr,M)O2 Nanocrystals for All‐Inorganic CsPbBr3 Perovskite Solar Cells

“…[23] According to previous reports,p artial substitution of Cr 3+ with divalent or trivalent cations such as Mg 2+ ,Ni 2+ ,Zn 2+ ,and Fe 3+ can significantly improve the electrical conductivity and carrier concentration, with an enhanced conductivity up to 220 Scm À1 . [24] Inspired by this,w ep ropose the use of Msubstituted (M = Ba 2+ ,C a 2+ ,o rN i 2+ )C u(Cr,M)O 2 nanocrystals as efficient HTMs in all-inorganic CsPbBr 3 PSCs with an architecture of fluorine-doped tin oxide (FTO)/c-TiO 2 /m-TiO 2 /CsPbBr 3 /Cu(Cr,M)O 2 /carbon. By tuning the VBM edges of Cu(Cr,M)O 2 nanocrystals,t he optimal device achieves ac hampion PCE as high as 10.18 percent and demonstrates nearly unchanged performance after storing in 80 %h umidity without encapsulation for 60 days or 80 8 8C conditions over 40 days,m ainly attributing to an enhanced hole conductivity and graded energy alignment between Cu(Cr,M)O 2 and carbon similar to abi-layered HTM.…”