The authors report the synthesis of ZnO nanorods on flexible and transparent mica substrates. The coupled use of polyethylenimine and ammonium hydroxide provided a direct method for growing vertically well-aligned ZnO nanorods with a high aspect ratio. Using mica as a substrate material enabled thermal annealing processes, which improved the structural and optical properties of ZnO nanorods with uniform surface coverage and excellent adhesion, increased transmittance of indium tin oxide (ITO)/mica (52%), and decreased sheet resistance of ITO/mica (80%). We have fabricated ZnO nanorod-based dye-sensitized solar cells (DSSCs) and piezoelectric nanogenerators (NGs) and investigated their annealing effects on the device performances. Specifically, the thermal treatment at 500°C for 30min increased the energy conversion efficiencies of DSSCs by 53%. Furthermore, we observed a three-fold increase in the NG׳s output voltage and output current density through this thermal annealing process. As shown below, mica, which can function under extremes of temperature, is useful as a substrate for flexible and transparent electronics.