Numerical simulation of the defect density influence on the steady state response of a silicon-based p–i–n cell

Abstract

This paper is concerned with the numerical simulation of the defect density influence on the steady state response of a silicon-based p-i-n cell under reverse bias dark conditions. To show this effect, the numerical simulation is performed on a crystalline cell containing a single discrete level of defects in the energy gap and in which the density of defects is varied. Afterwards, we extend our model to a typical amorphous silicon cell by including band tails and dangling bonds. The density of dangling bonds is calculated according to the defect pool model. For both cases, a detailed description of the physical model and its mathematical formulation is presented. By analysing the different variables which describe the electrical behaviour of the cell in the steady state such as the free carrier distributions, the carrier lifetimes and the quasi-Fermi levels, we show how the density of defects changes the semiconductor regime from lifetime to relaxation.

Computer simulation of the a-Si:H p–i–n solar cell performance sensitivity to the free carrier’s mobilities, the capture cross sections and the density of gap states

“…The thicknesses of the p, i and n layers are fixed, respectively equal to 16, 640 and 40 nm, where the activation energies at the p and n layers are, respectively, E fp = 0.19 eV and E fn = 0.1 eV, similarly to [20]. The input parameter values used to obtain the best agreement with the experimental measurements of [20] are 2 and σ nt = 1 × 10 −17 cm 2 , while the remaining parameters are the same as the ones indicated in table 1. The results obtained are summarized in table 2, from which we find that the agreement is satisfactory.…”

“…The a-Si:H p-i-n solar cell is treated as a one-dimensional device. Our simulation program developed previously [2,3], simultaneously solves the Poisson equation and the two continuity equations of free carriers [4,5] under steady state conditions, using the coupled method of Newton. This is performed by taking into account the usual model of the a-Si:H gap density of states, consisting of the band tails and dangling bond states [6,7].…”

“…Further, the density of states is calculated according to the defect pool model of Powell and Deane [13] which differs form previously proposed numerical models that adopt Gaussian distributions to describe the dangling bond density of states [8][9][10][11][12]. Moreover, a spatial distribution of this density along the device, as a consequence of the variation of the Fermi-level position within the energy gap is considered [2,3]. In addition, we have assumed a thin p/i interface layer with a high density of dangling bond states [8,9,14,3].…”

“…In our study, we try to shed light on a number of factors that limit cell performance in the single p-i-n junction. This is done through a computer simulation model [2,3], which presents a good tool for studying the electrical transport properties within the device, and for understanding the role of several parameters related either to the material properties (gap mobilities, density of states, etc) or to the cell structure (doping, layer's thicknesses, etc). In this work, we have particularly focused on the effects of the free carrier's mobilities, the capture cross sections of both tails and dangling bond states, and the i-layer density of states (DOS), on the output photo-parameters of the proposed solar cell, i.e., the short-circuit current density (J sc ), the open-circuit voltage (V oc ), the fill factor (FF), and the conversion efficiency (η).…”

Numerical simulation and analysis of the dark and illuminatedJ–Vcharacteristics of a-Si-H p–i–n diodes

“…These defects have, therefore, an important role in determining the diode performances. In this work, numerical simulations, using a transport model [14] extended to the studied situation, are performed in order to investigate the sensitivity of the dark J -V characteristic to two parameters, i-layer thickness and measurement temperature, taking into account the presence of the defect states at the interfaces. The obtained results are compared to the experimental measures of Matsuura et al [5].…”