Optoelectronic characterization of Zn_1-xCd_xO thin films as an alternative to photonic crystals in organic solar cells

Zn1−xCdxO thin films spanning the whole composition range have been explored as an active region in photonic devices. The precise control of the Cd concentration, as well as its crystalline phase, allowed to characterize their optoelectronic properties. However, its application as a transparent conducting oxide material in photonics has yet to be unveiled. Here, we fabricated Zn1−xCdxO thin films via the spray pyrolysis method and confirmed their composition via Energy-dispersive X-ray spectroscopy measurements. We obtained their dielectric function through spectroscopy ellipsometry over the 300-3200 nm wavelength range and validated our model performing transmittance measurements. We observed a nonlinear red-shift of the optical bandgap while increasing Cd concentration, from 3.2 eV for ZnO to 2.9 eV for Zn0.10Cd0.90O. We found that the samples with Cd concentration > 50% have sheet resistance as low as 19.8 Ω/Square. The use of alloyed metal oxides on organic solar cells as photonic crystal structures (PhC) was also evaluated by performing finite-difference time-domain simulations. We saw an enhancement in the light absorption leading to a 39.75% increase of the short-circuit current for Zn0.25Cd0.75O PhC when compared to organic solar cells with no PhC structure.