Size-controlled Si quantum dots embedded in B-doped SiNx/Si3N4 superlatice for Si quantum dot solar cells

Abstract

Under the condition of the fixed Si3N4 layer thickness of 1.1 nm, Si-QDs embedded in B-doped SiNx/Si3N4 multilayer thin films with various SiNx layer thickness were fabricated respectively. Si-QDs with controllable and nearly uniform size were formed in SiNx layers, and found that the optical band gap of the films can be adjusted by changing the thickness of SiNx layer. On the basis of this, the Si-QDs/c-Si heterojunction solar cells were prepared. It is found that the larger the band gap is, the higher the cell efficiency is. The best performance device is obtained with average QD size of ~3.5 nm, which has the highest efficiency of 7.05 % compared with the other two devices. This difference is caused by the difference of the spectral response of these devices.

Full text

Size-controlled Si quantum dots embedded in B-doped SiN
x
/Si
3
N
4
superlatice for Si quantum dot solar cells
Xiaobo Chen
1
•Wen Yang
2
•Peizhi Yang
2
•Junbao Yuan
2
•Fei Zhao
2
•
Jiabo Hao
3
•Yu Tang
3
Received: 23 June 2016 / Accepted: 29 August 2016 / Published online: 22 September 2016
ÓSpringer Science+Business Media New York 2016
Abstract Under the condition of the fixed Si
3
N
4
layer
thickness of 1.1 nm, Si-QDs embedded in B-doped SiN
x
/
Si
3
N
4
multilayer thin films with various SiN
x
layer thick-
ness were fabricated respectively. Si-QDs with controllable
and nearly uniform size were formed in SiN
x
layers, and
found that the optical band gap of the films can be adjusted
by changing the thickness of SiN
x
layer. On the basis of
this, the Si-QDs/c-Si heterojunction solar cells were pre-
pared. It is found that the larger the band gap is, the higher
the cell efficiency is. The best performance device is
obtained with average QD size of *3.5 nm, which has the
highest efficiency of 7.05 % compared with the other two
devices. This difference is caused by the difference of the
spectral response of these devices.
1 Introduction
All-Si tandem solar cell with a c-Si bottom cell is one of
the promising next-generation solar cells to overcome the
Shockley–Queisser efficiency limit for single-junction
solar cells [1,2]. Silicon quantum dots (Si-QDs) films are a
prime candidate for the top cell of an all-Si tandem solar
cell, with higher band gap than that of c-Si, tuneable by
adjusting QD size [3]. The growth of Si-QDs through the
use of SiN
x
/Si
3
N
4
multilayer is an effective way for the
preparation of silicon nitride based Si-QDs thin films with
controllable size, uniform and high-density [4,5]. The
purpose of the Si
3
N
4
layer is mainly to limit the size of Si-
QDs, especially in the direction perpendicular to the film
surface. However, the Si
3
N
4
layer is an insulating layer,
which is detrimental to the vertical electrical conductivity
of the thin film. Therefore, it is hoped that the thickness of
the Si
3
N
4
layers is as thin as possible. Ultra-thin Si
3
N
4
layers are used as the barriers, which are preferable for
carrier transport. So et al. [4] have found that 1 nm thick
ultra-thin Si
3
N
4
layers were sufficient in retraining the
growth of Si-QDs within the SiN
x
layers even after high
annealing processes. In Di et al.’s work [6], size-controlled
Si-QDs in SiO
2
/Si
3
N
4
hybrid matrix on quartz substrates
were successfully synthesized by magnetron sputtering of
alternating silicon rich oxide and 1 nm thick ultra-thin
Si
3
N
4
layers followed by different post-deposition anneals.
This work aims to discuss the potential use of SiN
x
/
Si
3
N
4
multilayer films as the absorber layer in Si-QDs/c-Si
heterojunction solar cells, which may facilitate the fabri-
cation of all-Si tandem solar cells. Towards this goal, we
report on structural, optical, and electronic properties of
B-doped Si-QDs/Si
3
N
4
multilayer films for Si-QDs/c-Si
heterojunction solar cells. Then, we discuss the perfor-
mance of the Si-QDs/c-Si heterojunction solar cells.
2 Experimental
Alternating Si
3
N
4
and B-doped SiN
x
multilayers were
deposited on one-side polished n-type (P-doped, with a base
resistivity of 1–5 Xcm) Si (100) substrates and quartz
&Peizhi Yang
pzhyang@hotmail.com
1
School of New Energy and Electronic Engineering,
Yancheng Teachers University, Yancheng 224051, China
2
Key Laboratory of Education Ministry for Advance
Technique and Preparation of Renewable Energy Materials,
Institute of Solar Energy, Yunnan Normal University,
Kunming 650092, China
3
School of Intelligent Manufacturing, Sichuan University of
Arts and Science, Dazhou 635000, China
123
J Mater Sci: Mater Electron (2017) 28:1322–1327
DOI 10.1007/s10854-016-5663-2
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