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Motivated by recent measurements of the number density of faint AGN at highredshift, we investigate the contribution of quasars to reionization bytracking the growth of central supermassive black holes in an update of theMeraxes semi-analytic model. The model is calibrated against the observedstellar mass function at $z\sim0.6-7$, the black hole mass function at$z\lesssim0.5$, the global ionizing emissivity at $z\sim2-5$ and the Thomsonscattering optical depth. The model reproduces a Magorrian relation inagreement with observations at $z<0.5$ and predicts a decreasing black holemass towards higher redshifts at fixed total stellar mass. With theimplementation of an opening angle of 80 deg for quasar radiation,corresponding to an observable fraction of ${\sim}23.4$ per cent due toobscuration by dust, the model is able to reproduce the observed quasarluminosity function at $z\sim0.6-6$. The stellar light from galaxies hostingfaint AGN contributes a significant or dominant fraction of the UV flux. Athigh redshift, the model is consistent with the bright end quasar luminosityfunction and suggests that the recent faint $z\sim4$ AGN sample compiled byGiallongo et al. (2015) includes a significant fraction of stellar light.Direct application of this luminosity function to the calculation of AGNionizing emissivity consequently overestimates the number of ionizing photonsproduced by quasars by a factor of 3 at $z\sim6$. We conclude that quasars areunlikely to make a significant contribution to reionization.

Dark-ages Reionization and Galaxy Formation Simulation - X. The small contribution of quasars to reionization