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In this study, tunneling mechanisms controlling the a-Si:H thin film/c-Si tandem solar cell were investigated employing numerical simulation. First, the effect of doped nc-Si:H tunnel recombination junction (TRJ) was studied with different structures. The band diagram, electric field, and recombination rate characteristics were investigated under a dark condition with doped nc-Si:H TRJ. The trap-assisted model and field-dependent tunneling were used to model the recombination and transport influence of the valence band offset (ΔEV) between the p-type layer of the top cell and TRJ in the high field region. Simulation results showed that the highest efficiency of 23.98% (Short circuit current density, Jsc = 18.74 mA cm−2, open circuit voltage, Voc = 1.565 V, fill factor, FF = 81.76%) could be obtained in the case of n/p nc-Si:H TRJ.

Al-doped ZnO (AZO) films were deposited onto glass substrates by RF magnetron sputtering for solar cell applications. The effects of the Al2O3 doping concentration on the structural, electrical, and optical properties of the AZO films were investigated. As the Al2O3 doping concentration was increased to 4.0 wt %, X-ray diffraction (XRD) showed a deterioration in the (002) peak intensity and a shift towards a higher angle. The best electrical properties (ρ= 9.8×10-4 Ω cm, µH = 22 cm2 V-1 s-1, and ne = 2.89×1020 cm-3) were obtained in the AZO sample containing 2 wt % Al2O3. Optical transmission >83% in the visible range was also observed and the optical bandgap was increased to 3.63 eV at an Al2O3 concentration of 4 wt %. For photoluminescence (PL) spectra, one UV emission peak at approximately 3.2 eV and a broad peak in the visible range from 2.3 to 2.7 eV were observed at Al2O3 doping concentrations ranging from 0–2.0 wt %. Blue emission at 2.67 eV, which indicates a non-stoichiometric structure, was only observed in the 4 wt % doped AZO films.