Abstract: A method of forming a solar cell structure is provided, which includes forming a metal electrode on a substrate, forming an absorber layer on the metal electrode, and forming a buffer layer on the absorber layer. The method also forms a titanium oxide layer on the buffer layer, wherein a thickness of the titanium oxide layer is greater than 0 and less than 10 nm. The method further forms a transparent conductive oxide layer on the titanium oxide layer. The step of forming the titanium oxide layer is atomic layer deposition (ALD) performed at a temperature of 100° C. to 180° C. with a precursor of titanium tetraisopropoxide.