Using a Taylor series expansion for the Fermi-Dirac occupation func-tion,an accurate analytical model is developed for calculating the trapped-charge density in a-Si:H considering deep and tail states simultaneously without simplification.This is followed by the investigation of the relative errors of the localized trapped charge density in a-Si:H at all temperatures as a function of the quasi-Fermi levll in the band gap cal-culated from three published analytical models and our above model.The results suggest that the relative errors of all these models increase notably as Efn is very closed to Ec(e.g.,-0.01eV