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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

Septina, Wilman, Kurihara, Masaaki, Ikeda, Shigeru, Nakajima, Yasuhiro, Hirano, Toshiyuki, Kawasaki, Yoshihito, Harada, Takashi, Matsumura, Michio
ACS Applied Materials & Interfaces 2015 v.7 no.12 pp. 6472-6479
coatings, copper, glass, photovoltaic cells, pyrolysis, sodium, sodium nitrate, sulfides, thiourea
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 °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 (Nₐ = 7.2 × 10¹⁷ cm–³) and the addition of sodium led to a more favorable value for solar cell application (Nₐ = 1.8 × 10¹⁷ 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%.