Design and Device Modeling
of Lead Free CsSnI3 Perovskite Solar Cell
Sweta Minj, Naman Shukla,
School of Studies in
Electronics and Photonics, Pt. Ravishankar Shukla University, Raipur-492010,
Research of lead-free Perovskite based solar cells has gained
speedy and growing attention with urgent intent to eliminate toxic lead in Perovskite
materials. The main purpose of this work is to supplement the research progress
with comparative analysis of different lead-free Perovskite based solar cells
by numerical simulation method using solar cell capacitance simulator
(SCAPS-1D) software. The environmental friendliness and excellent thermal
stability proves Cesium Tin Iodide (CsSnI3) as one of the promising
materials for the commercialization of the Perovskite solar cells. However,
CsSnI3 solar cells suffer from poor efficiency due to having low
open-circuit voltage, VOC attributed to poor absorber film quality
as well as energy level mismatch at the interfaces between different layers
like transparent front contact. The architecture of the solar cell is n-i-p
device structure acts as light CsSnI3 absorber active layer, TiO2 as electron transport
layer and Spiro-OMeTAD as hole transport layer with device structure FTO/ TiO2/CsSnI3 / Spiro-OMeTAD /Au. The open circuit voltage Voc, short circuit current density Isc, fill factor and power
conversion efficiency Voc=1.09V, Jsc=28.85mA/cm2,
FF=88.65%, eta=28.09%, V_MPP=0.99V, J_MPP=28.15 mA/cm2 respectively.
Keywords — Perovskite
Solar Cell, Lead-free, CsSnI3, SCAPS 1D
Perovskite solar cells have experienced a major leap in their
power conversion efficiency (PCE) just over a decade due to their very simple
manufacturing process, comparatively low processing cost, high absorption
coefficient, low surface recombination rates and relatively high efficiency. It
has increased from 3.8% in 2009 reported by Miyasaka and his colleagues in 2009 (Kojima et al., 2009) to 25.5% till
date (NREL, Best research-cell efficiencies)
in single-junction architectures, which is quite close enough to the
crystalline silicon solar cells at 26.7%. The hybrid organic-inorganic
perovskites have opened new doors towards more efficient light harvesting
materials. Owing to the property of tunable frequency, these solar cells can be
quite effective in absorbing different light frequencies by different layers
which can lead to a boost in their efficiencies unlike the conventional solar
cells. Despite this, lead based perovskites have two major challenges: a) poor
stability which is being addressed by improved device engineering and
encapsulation as well as incorporating the use of perovskites, b) high toxicity
that is raising a concern on an environmental level. Lead free perovskite
materials, which are non-toxic and are also being looked upon as another
alternative. These lead free materials will be a preference in the solar cell
market which will help in commercialization of perovskite solar cells if they
do not compromise with the device performance. Ideally, Pb-free perovskites
when used as light harvesting layers in solar cells, should have low toxicity,
high optical absorption coefficients, low exciton-binding, narrow direct band
gaps, high mobilities. Perovskites in the form of double perovskites, some
Sn/Ge based halides, and also some Bi/Sb-based halides with perovskite-like
structure show fascinating properties and are low-toxicity materials. Up to
2020, the highest efficiency for Sn-based perovskites has been reported to have
reached 13.24%. In these Pb-free perovskite materials, comparatively only
Sn-based PSCs have shown very promising performance. In Sn-based PSCs, certain
factors like the poor air-stability caused due to quick oxidation of Sn2+
leading to increased recombination losses, small formation energy of vacancies,
high intrinsic carrier density etc. leads to poor device performance as
compared to their corresponding lead-based analogues. The anti-bonding coupling
between Sn-5s and I-5p is comparatively weaker in FASnI3 (FA = CH (NH2)2)
than CsSnI3 and MASnI3 as a result of the larger ionic
size of FA which is also the reason behind the increase in formation energies
of Sn-vacancies. Along with experiments, simulation also plays a vital role in
analyzing various properties of these materials and the corresponding
performance parameters for various such materials. This work aids in studying
the relation of the properties with the parameters, comparing multiple
materials with the help of theoretical analysis by designing a device model.
Here, a comparative study of various Pb-free perovskites on a similar
configuration is done which helps us know about the distinguishing properties,
their impacts on device performance and further work for achieving high
efficiencies for Pb-free perovskites
The organic-inorganic halide perovskite (ABX3) solar
cells are emerging as the best contender for futuristic photovoltaic energy
harvesting process, which is evident from its tremendous growth of achieving
power conversion efficiency as high as 25.2% reported form single-cell till
to-date. Both the natural environment and humans. Therefore, there has been
growing interest in the development of alternative perovskites that use Sn
instead of Pb, such as CsSnI3. Tin-based halide perovskite materials
have been successfully employed in lead free perovskite solar cells. Recently,
several studies have revealed that the substitution of the methyl ammonium
cation by cesium (Cs) in the perovskite structure could significantly enhance
its thermal stability. Notwithstanding that the high-performance perovskite
cells are dominated by lead (Pb) based materials like Methyl Ammonium Lead
Halide, MAPbX3 (Shukla et al., 2021 and gopal et al., 2020) or
Formamidinium Lead Hallie (FAPbX3), the environmental impact of Pb
as well as high bandgap of these perovskite materials have always made
researchers think of its environmentally benign and low bandgap options, tin
(Sn) based perovskites like MASnX3 . Apart from this, inorganic
cations like Cesium (Cs) have been considering as the substitute of the organic
counter parts because of the instable ambient/outdoor performance of MAPbX3
and FAPbX3 due to the fragmentation of the organic components . Thus
Cesium Tin Iodide, CsSnI3 may be considered as one of the viable
choices for the commercialization of perovskite solar cells. However, CsSnI3
based solar cells suffer from lower efficiency. The stable
and efficient perovskite solar cells can be developed through optimization of
the solar cell device through experiments supported by data which is obtained by optical and
electrical simulations. In this
research work, the numerical
simulation of the CsSnI3 based
perovskite solar cell was done by using Solar Cell Capacitance Simulator
(SCAPS-1D). It is a one dimensional
solar cell simulator based on the drift diffusion physical model (Burgelman et
al., 2000).simulation of PSC. This software
tool has executed the semiconductor equation, the continuity equation of
carrier, Poisson equation, carrier
transport equations etc.
SCAPS software gives us the results by solving the basic semiconductor
equations, Poisson equations, the continuity equations for electrons and holes
and other carrier transport constraints (Burgelman et al.,2013). Organic metal
halide perovskite is used as active layer in this simulation. Device
simulations have been performed according to the parameters given in the
literature summarized in Table 1 (Lin et al., 2014; Hima et al., 2019; Calado
et al., 2016; Isoe et al., 2020).The n-i-p device structure is FTO/ TiO2/
Spiro-OMeTAD /Au. For optimized design of the solar cell for above structure,
short circuit current density Jsc,
open circuit voltage Voc,
fill factor FF and efficiency are Voc= 1.09V, Jsc=28.85mA/cm2,
FF= 88.65%, eta= 28.09%, V_MPP=0.99 V, J_MPP=28.15 mA/cm2
Figure 1. Architecture of simulated model
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