Cu(In,Ga)Se2 solar cell with Zn(S,O) as the buffer layer fabricated by a chemical bath deposition method

Abstract

Zn(S,O) polycrystalline thin films were prepared using chemical bath deposition. The Zn(S,O) thin film with high-crystalline quality fully covered the substrate by controlling concentrations of starting materials, temperature of the substrate, and reaction time. The obtained Zn(S,O) thin films were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The optical transmittance of the Zn(S,O) thin film with a thickness of 106.84 nm exceeded 90% in the wavelength range of 350–1400 nm. The obtained Zn(S,O) films were applied as buffer layers in the CuIn1−xGaxSe2 (CIGS) solar cells. By optimizing the thickness and quality of the buffer layer and using light soaking, a 11.65%-efficiency CIGS solar cell was obtained without an anti-reflective coating layer. The short-circuit current density increased compared with that of CIGS solar cell with cadmium sulfide buffer layer due to the higher band gap of Zn(S,O) than that of CdS. The increase of the efficiency with the light-soaking time was mainly due to the fill factor increase. The CIGS solar cell showed good weak light effect and high stability. The dominant recombination mechanisms in the CIGS solar cell with Zn(S,O) buffer layer were the tunneling-enhanced recombination in the space charge region and the interface recombination at the Zn(S,O)/CIGS interface.