Cu(In,Ga)(S,Se)2 Thin Film Solar Cell with 10.7% Conversion Efficiency Obtained by Selenization of the Na-Doped Spray-Pyrolyzed Sulfide Precursor Film

Selenium-rich Cu(In,Ga)(S,Se)(2) (CIGSSe) thin films on an Mo-coated soda-lime glass substrate were fabricated by spray pyrolysis of an aqueous precursor solution containing Cu(NO3)(2), In(NO3)(3), Ga(NO3)(3), and thiourea followed by selenization at 560 degrees C for 10 min. We studied the effects of intentional sodium addition on the structural and morphological properties of the fabricated CIGSSe films by dissolving NaNO3 in the aqueous precursor solution. The addition of sodium was found to affect the morphology of the final CIGSSe film: the film had denser morphology than that of the CIGSSe film obtained without addition of NaNO3. Photoelectrochemical measurements also revealed that the acceptor density of the nondoped CIGSSe film was relatively high (N-a = 7.2 x 10(17) cm(-3)) and the addition of sodium led to a more favorable value for solar cell application (N-a = 1.8 x 10(17) cm(-3)). As a result, a solar cell based on the sodium-modified CIGSSe film exhibited maximum conversion efficiency of 8.8%, which was significantly higher than that of the cell based on nondoped CIGSSe (4.4%). In addition, by applying MgF2 antireflection coating to the device, the maximum efficiency was further improved to 10.7%.