Improved micromorph solar cells by means of mixed‐phase n‐doped silicon oxide layers

Abstract

A good light trapping scheme is necessary to improve the performance of amorphous/microcrystalline silicon tandem cells. This is generally achieved by using a highly reflective transparent conducting oxide/metal back contact plus an intermediate reflector between the component cells. In this work, the use of doped silicon oxide as alternative n‐layer in micromorph solar cells is proposed as a means to obtain high current values using a simple Ag back contact and no extra reflector between the component cells n‐doped silicon oxide layers with a wide range of optical and electrical properties have been prepared. The influence of different deposition regimes on the material properties has been studied. The main findings are the following: (i) when carbon dioxide is added to the gas mixture, sufficiently high hydrogen dilution is necessary to widen the transition region from highly conductive microcrystalline‐like films to amorphous material characterized by low electrical conductivity; (ii) lower refractive index values are found with lower deposition pressure. Optimal n‐doped silicon oxide layers have been used in both component cells of micromorph devices, adopting a simple Ag back contact. Higher current values for both cells are obtained in comparison with the values obtained using standard n‐doped microcrystalline silicon, whereas similar values of fill factor and open circuit voltage are measured. The current enhancement is particularly evident for the bottom cell, as revealed by the increased spectral response in the red/infrared region. The results prove the high potential of n‐doped silicon oxide as ideal reflector for thin‐film silicon solar cells. Copyright © 2011 John Wiley & Sons, Ltd.

Use of hexamethyldisiloxane for p-type microcrystalline silicon oxycarbide layers

“…Function n p-μc-SiOx:H p-type layer 2.97-3.5 [5,13] n-μc-SiOx:H n-type layer + IRL 1.8-2.6 [9,10,14,15] SiOx IRL 2.0 [12,16] Table 1 gives a summary of n values reported in the literature for such films. The electrical conductivity of doped μc-SiO x :H is attributed to the presence of doped microcrystalline silicon filaments in an amorphous silicon oxide matrix, which results in an out-of-plane conductivity of the layers above 10 −5 S/cm, while their in-plane conductivities are below 10 −10 S/cm [9].…”

“…In particular, doped microcrystalline silicon oxide (μc-SiO x :H) is a material which has gained scientific interest because of it having a reduced optical absorption and low refractive index, while still generating sufficient built-in potential across the absorber layer for electron-hole separation [5][6][7][8]. It has been demonstrated that it is possible to control the refractive index (n) of undoped and doped μc-SiO x :H in the range from 1.8-3.6 [9][10][11] and that these layers can be designed for several functions in thin film silicon solar cells, namely as a doped layer or as an intermediate reflector layer (IRL) [12]. a e-mail: prabal.goyal@polytechnique.edu Table 1.…”

Light harvesting schemes for high efficiency thin film silicon solar cells

“…-Improve the light management [9][10][11][12][13][14]: transparent intermediate reflector layer in micromorph solar cells and reduced parasitic absorption (for instance highly transparent window layer). -Increase electrical performance and cell resilience to the substrate texture [1,[5][6]: electrical performance gain scales with substrate roughness, and up to 6 % and 20 % gains were demonstrated respectively for a-Si:H and μc-Si:H p-i-n junctions [1].…”

Amorphous single‐junction cells for vertical BIPV application with high bifaciality

“…• the CO 2 concentration • the doping concentration • the layer thickness We decided to use an amorphous n-layer instead of the commonly used μc-Si 1-X O X :H layer [9,10] because we expected a better long-term stability of highly doped amorphous n-layers compared to highly doped μc-Si 1-X O X :H layers [work in prep.]. Furthermore, the process stability is better.…”