In this letter we have made a comparative study of degradation of solar EUV radiation and EUV-generated photoelectrons in the inner comae of comets having different gas production rates, Q, with values 1 ¿ 1028, 7 ¿ 1029, 1 ¿ 1031, and 1 ¿ 1032 s-1. We found that in higher-Q comets the radial profile of H2O+ photo-production rate depicts a double-peak structure and that the differences in sunward and anti-sunward photoionization rates are pronounced. We show that photoelectron impact ionization is an order of magnitude larger than photoionization rate near the lower photoionization peak in comets with Q > ~1 ¿ 1031 s-1. The present study reveals the importance of photoelectrons relative to solar EUV as the ionization source in the inner coma of high-Q comets.