Feasibility of using thin crystalline silicon films epitaxially grown at 165 °C in solar cells: A computer simulation study

Abstract

We have previously reported on the successful deposition of heterojunction solar cells whose thin intrinsic crystalline absorber layer is grown using the standard radio frequency plasma enhanced chemical vapour deposition process at 165 • C on highly doped P-type (100) crystalline silicon substrates. The structure had an N-doped hydrogenated amorphous silicon emitter deposited on top of the intrinsic epitaxial silicon layer. However to form the basis of a solar cell, the epitaxial silicon film must be chiefly responsible for the photo-generated current of the structure and not the underlying crystalline silicon substrate. In this article we use detailed electrical-optical modelling to calculate the minimum thickness of the epitaxial silicon layer for this to happen. We have also investigated by modelling the influence of the a-Si:H/epitaxial-Si and epitaxial-Si/c-Si interface defects, the thickness of the epitaxial silicon layer and its volume defect density on cell performance. Finally by varying the input parameters and considering various light-trapping schemes, we show that it is possible to attain a conversion efficiency in excess of 13% using only a 5 micron thick epitaxial silicon layer.

Detailed analysis of III-V/epi-SiGe tandem solar cell performance including light trapping schemes

“…We have modeled the tandem solar cell using TCAD numerical simulation tools [16], which solve the Poisson, electroneutrality and transport equations (Drift Diffusion) self-consistently on a 2D mesh. Band structure, electrical transport and recombination parameters for III-V materials and amorphous and crystalline silicon were chosen in agreement with literature values [17][18][19][20][21][22] and are composition and doping dependent. To simulate the current density versus voltage characteristics, J(V), under AM1.5 g spectrum, realistic photogeneration profiles have been calculated through the entire structure, neglecting optical shading due to metal contacts and using the optical indexes of the various layers as inputs.…”

“…To validate our bottom cell model, we have simulated four epi-Si(Ge) heterojunction solar cells that were formerly fabricated using low-temperature plasma enhanced chemical vapor deposition (PECVD) process to demonstrate the feasibility of using thin epitaxial layers as high quality absorbers [4,14,20,22]. As depicted in Fig.…”

“…To achieve this fit we have constructed an epi-Si model based upon [22], which was adapted to absorber thicknesses (t epi ) below 2.4 µm, and we have extended it for thicknesses of 3.2 µm and 4.2 µm and for epi-SiGe. Most important material parameters are given in Table 3.…”

“…Compilation of typical material parameters for epi-Si and epi-SiGe from Si and SiGe databases [17] for common parameters and from [21] for epi-Si electron and hole mobility (also used in [22] Table 4 Fitting parameters used in our models to reproduce experimental data in Fig. 3(b).…”

Study of Au/n-Ti₂S/p-Si/Al Schottky-Type Thin Film Heterojunction Solar Cells: Computer Simulation Modeling

“…Sufficient doping and layer thickness has to be chosen to introduce the band bending at the n-Ti 2 S/p-Si interface determining the built-in voltage and therefore the upper limit of V oc (Stangl et al, 2004;Leendertz et al, 2011;Schulze et al, 2011;Chen and Zhu, 2012). However, with high doping the junction recombination can increase V oc is lowered for doping concentration above a certain level (Chakraborty et al, 2013;Haque et al, 2013). A fundamental problem when contacting the ptype Si with the n-type n-Ti 2 S transparent conductive oxides TCO's is the formation of a Schottky barrier.…”