Post-annealing effects on the structural and optical properties of Zn(S,O) buffer layer for thin-film solar cells

Abstract

The structural and optical properties of Zn(S,O) buffer layers were investigated by post-annealing in air. As the annealing temperature increased to 500℃, the optical bandgap of the Zn(S,O) thin films decreased from 3.59 eV to 2.97 eV.This optical bandgap narrowing was correlated with the composition change of the films by post-annealing. The S/Zn ratio decreased from 0.60 to 0.47, as confirmed by EDX analysis. TheZn(S,O) thin film applied to blocking layer in dye-sensitized solar cells diminished the power-conversion efficiency. One possible reason is that the Zn(S,O) blocking layer prohibits the injection of electron from ZnO to FTO, because of thickZn(S,O) layer. Micrometer-sized polydispersed Al doped ZnO aggregates made up of nanoparticles were synthesizedby a hydrolysis method for photoelectrode in DSSCs. The Al doping on ZnO aggregates resulted the decrease ofopen-circuit voltage (Voc) and short-circuit current (Jsc). Consequently, the power-conversion efficiency decreased to 0.92%. The local strain and grain size of ZnO increased with increasing doping concentration.In addition,the morphology of ZnO nanoparticles that compose the aggregateswas changed to nanorod. The nanorodwill decrease the surface area for dye adsorption than nanoparticle and it may cause decreased cell efficiency.