In this paper, two solar cells n-i-p(+) and n-i-p-p(+) based on hydrogenated amorphous silicon (a-Si:H) and hydrogenated nanocrystalline silicon (nc-Si:H) have been simulated by using AMPS-1D (Analysis of Microelectronic and Photonic Structures) simulator. Various factors that affect cell performance have been studied, such as work function of Transparent Conducting Oxide ( W-TCO), and band gap and thickness of the i-a-Si:H absorber layer. At first the effect of work function W-TCO on the performances of both structures was studied. The best cell's external parameters where obtained in the case of n-i-p-p(+) structure. For this latter, the energy band diagram, current voltage characteristics T(V), the trapped hole density, the distribution of built-in electric field, and the quantum efficiency are calculated and analyzed in depth to understand the effect of W-TCO. It is demonstrated that, for high efficiency of solar cell, the W-TCO value should be high enough in order to enhance built-in potential, and gives the electric field negative and the front hole barrier height for a neutral (i.e., no band bending) contact at TCO/p(+)nc-Si:H interface. Later, band gap and thickness of i-a-Si:H absorber layer are optimized. Simulation results showed that the highest efficiency of 9.35% (J(SC) = 13.96 mA/cm(2); FF = 71.4%; V-OC = 936 mV) has been obtained in the case of n-i-p-p(+) structure, when values of W-TCO, i-a-Si:H band gap and i-a-Si:H layer thickness are 5.45 eV, 1.78 eV, and 550 nm, respectively. A comparison between simulation results and experimental data, showed that the conversion efficiency of n-i-p-p(+) solar cell can be enhanced from 7.44% to 9.35%, by using the optimized values. (C) 2015 Elsevier Ltd. All rights reserved.