We present a theoretical investigation of ZnO nanotubes square periodic array as an antireflective coating for a planar solar cell including Kesterite as a p-type absorber and Zinc Tin Oxide as an n-type buffer. The method of the calculation is rigorous coupled wave analysis. We found that this coating leads to a considerable reduction of the loss of the ideal short circuit current density by about 80 %. The optimal values of the nanotube diameter, nanotube height, array period and the absorber thickness are 438 nm, 150 nm, 438 nm and 1.5 µm respectively. The study of the variation of the loss of the ideal short circuit current density with the incident angle of the sunlight shows that the NTs array still has good anti-reflection characteristics as long as the incident angle doesn’t exceed 60°.