We report an experimental study on the fabrication and characterization of hierarchical graphene/metal grid structures for transparent conductors. The hierarchical structure allows for uniform and local current conductivity due to the graphene and exhibits low sheet resistance because the microscale silver grid serves as a conductive backbone. Our samples demonstrate 94% diffusive transmission with a sheet resistance of 0.6 Ω/sq and a direct current to optical conductivity ratio σdc/σop of 8900. The sheet resistance of the hierarchical structure may be improved by over 3 orders of magnitude and with little decrease in transmission compared with graphene. Furthermore, the graphene protects the silver grid from thermal oxidation and better maintains the sheet resistance of the structure at elevated temperature. The graphene also strengthens the adhesion of the metal grid with the substrate such that the structure is more resilient under repeated bending.

Heteroepitaxial, single-crystal-like Cu2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu2O films on low cost, flexible, textured metallic substrates. Cu2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu2O phase without any trace of CuO phase is only formed in a limited deposition window of P(O2) - temperature. The (00l) single-oriented, highly textured, Cu2O films deposited under optimum P(O2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40–60 cm2 V−1 s−1 and carrier concentration over 1016 cm−3. The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu2O solar cell based on epitaxial Cu2O film prepared on the textured metal substrate.

The addition of Ag nanoparticles (Ag NPs) with an average size of 30 nm into ZnO increases the electric conductivity up to 1000 times. While a similar increase in the conductivity is observed in a mixture of Ag nanoparticles and Al-doped ZnO (AZO) films, a physical mechanism underlying the change in electric conductivity is not the same for Ag NP-added ZnO and Ag NP-added AZO. In Ag NP-added ZnO, an ohmic junction is formed at the ZnO−Ag interface, and electrons are accumulated in ZnO near the ZnO−Ag interface until electron-rich islands are connected. However, in Ag NP-added AZO, electrons in Ag NPs move to the AZO matrix via thermionic emission and travel through the AZO matrix. This change in electron transport at ZnO−Ag and AZO−Ag interfaces is due to the fact that the work function of ZnO (4.62 eV) is larger than those of Ag (4.24 eV) and AZO (4.15 eV). An increase in Ag NP content in the ZnO matrix leads to the overlap of the electron accumulation regions and forms a percolation path for the electron transport without deteriorating the electron mobility. Hence, the electron concentration increases to 2.4 × 10 20 /cm 3 in the 1.4 vol % Ag NP-added ZnO film. In addition, Ag NPs have a negligible effect on the transmittance, and the best Haacke figure of merit (Φ H ) values are 2.86 and 5.18 for ZnO:Ag NP and AZO:Ag NP, respectively.

We have studied the detailed interface structure and energy conversion behavior of TiO2/PbS heterojunction solar cells. Nanoscale structure and composition analysis have revealed that thermal annealing causes intermixing of the TiO2 and PbS phases and influences the morphologies and optical properties of the heterojunction film. This intermixing increased the junction area within the depleted bulk heterojunction (DBH) layer and promoted the carrier extraction from PbS QDs to TiO2. In addition, the thermal annealing caused interparticle necking between PbS QDs and increased the crystallinity of the PbS QD film. Compared with unannealed PbS/TiO2 heterojunction solar cells, the formation of the DBH layer and the partial sintering of PbS QDs led to a doubling of the short-circuit current (J sc) and an improved energy conversion efficiency, by 39%. Electric force microscopy analysis confirmed the presence of a DBH layer. The electron lifetime and fill factor (FF) of the solar cells decreased when the TiO2/PbS mixed film was thermally annealed, and this was assigned to a lower recombination resistance in the DBH layer. Post-treatment of PbS/TiO2 DBH films with ethanedithiol was found to increase the recombination resistance at PbS/TiO2 interface and to enhance the energy conversion efficiency to ∼4%.

We report a comprehensive study on the optical and electronic properties of hierarchical metal nanomesh (NM)/microgrid (MG) structures to evaluate their performance as transparent conductors (TCs).