Ion Implantation‐Induced Bandgap Modifications in the ALD TiO2 Thin Films

Atomic layer deposited (ALD) TiO2 layers are implanted with N, O, and Ar ions to reduce the bandgap, thereby increasing its absorbance in the visible region. The implantation is accomplished with 40 keV nitrogen, 45 keV oxygen, and 110 keV argon ions in the fluence range 1 × 1015 to 5.6 × 1016 ions cm−2. The energy of each incident ion is tuned using stopping and range of ions in matter (SRIM) to produce defects around the same projected range. The structural analysis of the as‐deposited film is performed through X‐ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering (RBS), and time of flight elastic recoil detection analysis (ToF‐ERDA). The implanted layers are characterized using diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR) to study the optical and vibrational properties of the films. The results demonstrate that nitrogen implantation in TiO2 reduces the reflectance from 43.52% to 26.31% and bandgap from 2.68 to 2.61 eV, making it a promising bandgap‐engineered material for capping layers in solar cell applications. The refractive index of the 40 keV nitrogen ion implanted film at 1 × 1016 ions cm−2 (N‐16) increases from ≈2.8 to ≈2.95. OPAL2 solar cell simulations show that the N‐16 implanted TiO2 anti‐reflective coatings (ARC) can enhance the absorbed photocurrent by 7.3%.