Numerical Modeling and Simulation of Output Parameters in Poly-Si Homojunction nip (or pin) Solar Cells

摘要

Recently, a particular interest is given to polysilicon material in terrestrial photovoltaic conversion devices as solar cells with weak cost and several structures have been studied to improve the out put parameters. The aim of this work is to study the sensitivity of the light characteristics to various device and material parameters in nip (or pin) homojunction solar cells: the high density of trap states localized at the grain boundaries and at the two interfaces. For that, we have used a one dimension numerical resolution of transport equations in semiconductors (Poisson's equation and the two equations of continuity of electrons and holes) under AM1.5 solar lighting. In this simulation, we have taken into account the intrinsic properties of polysilicon material as a density of trapping states formed by two exponential band tails near the conduction and the valence band edges and gaussian state distribution for the dangling bonds. However, the results show that the evolution of fundamental photovoltaic parameters (fill factor, short circuit current, conversion efficiency and open circuit voltage) are strongly linked to polysilicon parameters. In the last, our simulation results have been compared with experimental current-voltage curve obtained on nip (pin) junction. The polysilicon has been deposited by low pressure chemical vapor deposition technique and eventually added with phosphine or diborane for doped layers where the time of deposition depend of thickness of intrinsic layer (≥3 μm). The highly doped layers (n~+ or p~+) have a thin thickness in order of 1000 to 1500A. Finally, these cells presents a weak efficiency in order of 0.2%, it is owed to the presence of an important trapped density found in intrinsic polysilicon layer and at interfaces.