Effect on Al₂O₃ Doping Concentration of RF Magnetron Sputtered ZnO:Al Films for Solar Cell Applications

Abstract

Al-doped ZnO (AZO) films were deposited onto glass substrates by RF magnetron sputtering for solar cell applications. The effects of the Al 2 O 3 doping concentration on the structural, electrical, and optical properties of the AZO films were investigated. As the Al 2 O 3 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 ( ¼ 9:8 Â 10 À4 cm, H ¼ 22 cm 2 V À1 s À1 , and n e ¼ 2:89 Â 10 20 cm À3 ) were obtained in the AZO sample containing 2 wt % Al 2 O 3 . Optical transmission >83% in the visible range was also observed and the optical bandgap was increased to 3.63 eV at an Al 2 O 3 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 Al 2 O 3 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.

Surface Characteristics, Optical and Electrical Properties on Sol-Gel Synthesized Sn-Doped ZnO Thin Film

“…1,2) They are widely applied in various optoelectronic devices, such as the active channel layer of thin film transistors (TFTs) 3,4) and the electrodes of organic light emitting devices or thin film solar cells. [5][6][7][8] Various technologies have been used to prepare ZnO-based thin films, such as RF/DC magnetic sputtering, 9,10) pulsed laser deposition (PLD), 11) chemical vapor deposition (CVD) 12) and the sol-gel method. 13,14) Among these techniques, the sol-gel method enjoys advantages of simplicity, safety, low cost and easy adjustment of composition.…”

Optoelectronic performances on different structures of Al‐doped ZnO

“…It can been seen that Al-doped ZnO (ZnO:Al, ZnO:Al-int) is a shallow donor defect and is propitious to the formation of N type ZnO semiconductors, this may also explain why the electrical properties of AZO is improved in some empirical conclusions. 10,14,15 It also can be inferred that the rationality of ZnO:Al and ZnO:Al-int structure exist in AZO films. ZnO:Al-O make the Fermi level move to the top of the valence band, illustrating the interstitial O acts acceptor in ZnO, it can be inferred that oxygen-enriched ZnO plays a poor role in the formation of N type ZnO semiconductors.…”

“…Figure shows the DOS different structures of Al‐doped ZnO, compared with DOS of pure ZnO, the DOSs of both ZnO:Al and ZnO:Al‐int result in the Fermi level band move to the bottom of the conduction band, which illustrates the Al atom acts as donor in doped ZnO, and Al atom does not introduce discrete defect levels in ZnO band gap, and the DOS near the Fermi level does not increase significantly. It can been seen that Al‐doped ZnO (ZnO:Al, ZnO:Al‐int) is a shallow donor defect and is propitious to the formation of N type ZnO semiconductors, this may also explain why the electrical properties of AZO is improved in some empirical conclusions . It also can be inferred that the rationality of ZnO:Al and ZnO:Al‐int structure exist in AZO films.…”

“…Samwel et al used ZnO:Al ceramic and Zn:Al metal alloy targets to prepare AZO thin films by DC magnetron sputtering, the band gap energy, electrical resistance, mobility, carrier concentration, and optical spectra were studied, they found that this method was fit for preparing AZO thin films. Jeong studied AZO films with an Al 2 O 3 doping concentration ranging from 0 to 4.0wt%, the results showed AZO (2wt% Al2O3) exhibit best electrical properties. Zhao et al analyzed the effect of the concentration of doped Al on ZnO based on first‐principles method, they demonstrated the electric conductivities and band gaps decreased with the increase in doping concentration.…”

Structure and Optical Properties of Al-Doped ZnO Nanodrums as Anti-Reflection Coating Material in Solar Cells

“…Meanwhile, the peak shift of (100) and (101) plane was not significant. The peak shift to larger diffraction angle indicated the inclusion of dopant Al 3+ ions which have a smaller radius than Zn 2+ ions into the lattice of ZnO [11][12]. Meanwhile, the shifted peak to a smaller diffraction angle was caused by a tensile voltage that raised distortion in the lattice of ZnO.…”