Effect of the interface states on the cell parameters of a thin film quasi-monocrystalline porous silicon as an active layer

doi:10.1016/j.mejo.2008.06.068

Microelectronics Journal

Volume 39, Issue 12, December 2008, Pages 1433-1438

https://doi.org/10.1016/j.mejo.2008.06.068 Get rights and content

Abstract

Unlike crystalline silicon, quasi-monocrystalline porous silicon (QMPS) layers have a top surface with small voids in the body. What is more pertinent to the present study is the fact that, at a given wavelength of interest for solar cells, these layers are often reported, in the literature, to have a higher absorption coefficient than crystalline silicon. The present study builds on existing literature, suggesting an analytical model that simulates the performance of an elementary thin QMPS (as an active layer) solar cell. Accordingly, the effects that the interface states located at the void–silicon interface and that the porosity of this material have on the cell parameters are investigated. Furthermore, the effects of the optimum base doping, QMPS thickness, and porosity on the photovoltaic parameters were taken into consideration. The results show that the optimum base doping depends on the QMPS thickness and porosity. For an 8 μm thickness, the film QMPS layer gives a 35.4 mA/cm² for short-circuit current density, 15% for conversion efficiency, and 527 mV for open-circuit voltage when the value of the interface states is about 10¹² cm⁻² and the base doping is about 2×10¹⁸ cm⁻³ under AM 1.5 conditions.

Introduction

The use of thin crystalline silicon solar cells, fabricated by various versions of large transfer processes, is one of the most promising approaches to achieve both high performance and low cost, and this is due to its low material cost and ease of manufacturing [1], [2], [3], [4]. Quasi-monocrystalline porous silicon (QMPS) is a very promising material for the production of inexpensive and efficient solar cells for terrestrial photovoltaic applications. Recently, such layers have been reported to have significantly higher absorption coefficient compared to crystalline silicon at the interesting range of the solar spectrum for photovoltaic solar cell applications [5], [6].

A semi-empirical model has been developed to account for the higher absorption coefficient of QMPS layer which predicts the absorption coefficient of QMPS layer for different thicknesses, porosities and void sizes [5]. The transport parameters, such as the minority carrier mobility and lifetime in QMPS layer, have also been reported [7], [8].

In QMPS the presence of voids in the body and interface states dramatically attenuates the electronic proprieties of this material and, consequently, its photovoltaic parameters. Extensive research has been carried out to understand the properties of the QMPS material and to suggest useful techniques and models to achieve high performance. Modeling the performance of QMPS cells has been the subject of several review papers [7], [8]. It is demonstrated that the recombination of minority carriers at void–silicon interface decreases the photovoltaic parameters of QMPS solar cells, particularly the open-circuit voltage [7].

The objective of this paper is to extend the theory developed by Banerjee et al. [7] to further investigate the effects of the density of interface states, physical parameters, namely porosity and void radii, and the optimum base doping on the photovoltaic parameters of thin QMPS solar cells.

Section snippets

Model calculation

The schematic structure for analyzing an n⁺p QMPS solar cell is shown in Fig. 1. The doping levels in the top and the base regions are assumed to be uniform; hence, no field exists outside the space charge regions. The voids in the body of the QMPS layer are assumed to be spherical in size and uniformly distributed.

Results and discussion

In this study we discuss the results of the calculation of the short-circuit current density J_sc, the open-circuit voltage V_oc and the conversion efficiency η of thin QMPS solar cells for different values of the cell thickness (H).

The results of the photovoltaic parameters presented in this paper are computed using the numerical values given in Table 1.

Conclusion

In this paper, an analytical model shows the potential of a thin solar cell. The model used a QMPS layer as an active layer and investigated it through by modeling and simulating the cell parameters. The effects that the interface states at the void–silicon interface and the porosity in this material have on cell parameters have been discussed. It was possible to conclude from our findings that a greater improvement in open-circuit voltage and efficiency can be achieved when the interface

Acknowledgments

Thanks are due to Mr. Smaoui Anwar, from the English department at the Sfax Faculty of Science for carefully proofreading and constructively revising this paper.

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Effect of the interface states on the cell parameters of a thin film quasi-monocrystalline porous silicon as an active layer

Abstract

Introduction

Section snippets

Model calculation

Results and discussion

Conclusion

Acknowledgments

Sol. Energy Mater. Sol. Cells

Sol. Energy

Sol. Energy Mater. Sol. Cells

Thin Solid Films

Solid-State Electron.

Solid-State Electron.

Sol. Energy Mater. Sol. Cells

Sol. Energy Mater. Sol. Cells