DOI: https://doi.org/10.21203/rs.3.rs-1265526/v1
Perovskite Solar Cells (PSC) research has increased noticeably in recent years as a result of significant improvements in their performance. Perovskite solar cells are a new development in Photovoltaic technology. Because PSCs are inexpensive, have the ability to tune the bandgap and are a promising future option for meeting cell efficiency limits and strong broad optical absorption. Toxicity is an important factor in the development of organic and inorganic Perovskite solar cells. PSCs based on Sn are a worthy competitor to PSCs based on Lead (Pb). The majority of them used Methylammonium tin iodide (CH3NH3SnI3) material as an absorber layer because it has greater absorption but suffers from temperature instability. As a result, in this work, we use Formamidinium tin iodide (FASnI3) absorber, which has higher temperature stability than CH3NH3SnI3 Methylammonium tin iodide with a band gap of 1.4 eV. Solar cell Capacitance simulation used in this work to create FASnI3-based solar cells. This paper proposes a Power Conversion Efficiency of 24.22% for PSCs. For maximum Power Conversion Efficiency (PCE), the optimized thickness values are 10 nm for CuI (Hole transport layer), 850 nm for FASnI3, and 20 nm for ZnOS (Electron Transport Layer). The best temperature range for device performance is around 340K. SCAPS was used to calculate the current work. In addition, we demonstrated that ZnOS is the most promising ETL as a TiO2 replacement in this work. The proposed work focuses on paving the way for novel eco-friendly non-toxic PSCs as well as investigating optimised Voltage output circuit (Voc), Current density (Jsc), Fill factor (FF), and Power conversion Efficiency (PCE) device characteristics.
Nowadays Perovskite solar cell is the mainstream in PV technology with high PCE and PSCs is the best competitor for Si-wafer based solar cells [1]. Recently in perovskite solar cell, halides-based PSCs has the most promising absorber materials in PSCs [2]. The power conversion efficiency of PSCs which is based upon Pb-PSCs had a dramatic improvement from 3.08% to recently certify the value of 25.5% [3]. However, there are some shortcomings faced on Pb based PSCs. Like toxicity, thermal stability, air stability and non-ecofriendly to the humans. These are some of the disadvantages for Pb-based PSCs [4]. For that reasons pollution free and safety to humans, it is emergently needed to develop a nontoxic or low toxic metal to replace the Pb based ab-layer of PSCs. Therefore, research had to be made to replace Pb with some low and nontoxic materials in PSCS [5]. Sn, Cu, Bi, and Sb have all been studied as potential replacements for Pb-PSCs [6]. Sn has emerged as the most promising immediate replacement material for Pb-based PSCs among these. Because Sn belongs to the same group as Pb in the periodic table, its electric and optical properties are too similar, making Sn the best replacement material in PSCs [7].
The general formula for organic and inorganic halide perovskite solar cells is ABX3, where A and B are cations and X is always a halogen. MA, FA, and Cs are the most commonly used cations (A) in PSC [8]. From 4th and 7th, group elements are widely used as a B cation and X halogen respectively [9]. In this work, we use Sn be the replacement of Pb. Sn is not only for the alternative ion to Pb, it is also to enhance ecofriendly of PSCs [10]. Due to temperature instability in CsSnI3 and MASnI3 we use the FASnI3 as the Ab-layer in this simulated work [11]. FASnI3 had a more solid perovskite structure, more stable and also the air stability is high compared with MASnI3. These are the reasons we use FASnI3 having a perovskite layer for this simulated Device. Recently many approaches have been done to improve the FASnI3 based device [12]. FASnI3 has higher carrier mobility than MASnI3 according to Milot et al [13]. Krishna moorthy groups published the first study on FASnI3-based PSCs in 2015, with an efficiency of 1.41 percent [14]. FASnI3 with Eg (1.4eV) which is wider than MASnI3 and CsSnI3 (1.30eV) respectively and narrow to Pb based PSCs. Also, in FASnX3 can be tuned the Eg with different halides [15]. Recently CuI had attained PCE 17.6% which is based upon spray deposition method [16]. CuI had a high electric conductivity compared with Spiro-MeOTD. For that reason, we use CuI as a HTM in this work. CuI [17]. Bansal had investigated MASnI3 based solar cell with different ETL and HTL they achieved the PCE 21.1% in that ZnOS act as ETL [18]. Currently, before fabricating a cell or a device, the theoretical studies help more to understand and find the behavior of the cell Devices [19]. In recent days, many simulation devices are studied for PSCs with novel materials in SCAPS (1D) [20]. The initial structure is based on an 11.01% working PCE. After several optimizations on the thickness of the ab-layer, HTL and ETL, the simulated devices achieve an efficiency of 24.22%. At this present work, we optimized Novel FASnI3 based Perovskite solar cell with CuI and ZnOS act as a very promising HTL and ETL respectively. Replacement of Spiro-MeOTD and TiO2 and also FASnI3 material is the best replacement for MASnI3 based solar cell.
The device's simulated configuration is FTO / ZnOS / FASnI3 /CuI /Au. To date, three types of PSCs have been investigated: mesoporous planar, and inverted planar. The inverted planner configuration has been completed in this work and is shown in Fig. 1. (a) Device configurations of simulated PSCs, CuI as HTL and ZnOS as ETL. Energy band diagram for this device also shown in Fig (b). In Fig. 1(c, d) shown the initial Jsc, Voc, and %PCE- wavelength studies. All the basic parameters are collected from various research papers and tabulated in Table.1 [3, 10, 15, 21, and 22]. Meng and his group report that at low temperature the inverted planar would exceed over 18% of efficiency flexibility with J-V hysteresis [23]. Table.2. Summaries the Nt, ND, NA, for the configuration of the device and the work function of front and back contact as FTO (4eV) and Au (5.1 eV) respectively [24, 25].
The simulated was performed in SCAPS 1D under AM 1.5G illumination. This simulation carries only inside the SCAPS-1D and mainstream to derive from the following fundamental equations Poisson, hole and electron continuity. All the simulated results were examined in separate sections through graphs for each stage. In initial structure results, values of is PCE 11.01%, after several optimization on the absorber layer, HTL, ETL, and temperature in this device we constructed a novel PSCs with high efficiency.
The temperature of the solar cell has an effect on its overall performance. In this simulation, we kept the temperature constant at 300K at first and then varied it from 300K to 400K to determine the effect of working temperature on PCE, Voc, Jsc, and FF for the best ab-layer thickness, as shown in fig. In this simulated device, it was discovered that as the temperature increased, the PCE, Voc, Jsc, and FF of the solar cell decreased, because of carrier concentrations, charge carrier mobility and the material's bandgap at high temperatures (mariSoucase, et.al.2016). The efficiency slightly decreased from 24.09–23.64% at (300-400) K. The diffusion length reduces and series resistance increases. The resultant is decreased in PCE and FF (Mandadapu and group at 2017), because of the increase in energy enhanced recombination, electrons become unstable at higher temperatures in a solar cell, resulting in a low PCE (Mandadapu 2017). For that 340k is the working temperature for this simulation work.
The ab-layer in PSCs absorbs photons from sunlight whose energy is greater than the bandgap of the ab-layer, which causes excisions. These preciseions are essentially charged electron-hole pairs. To maximize PCE, it is necessary to understand the impact of defect density on PSC performance. Because the Ab-layer is a critical factor in determining the performance of PSCs, its effect on solar cell output parameters has been studied using simulation. The active layer thickness was increased from 100 nm to 1050 nm in 850 nm increments and the effect on performance parameters is shown in Fig. (3). The device's performance is excellent at 850 nm, and it achieves the maximum efficiency. At 850 nm, the device's performance is excellent, with the maximum efficiency of 24.22% achieved by using Voc 6.20 V, Jsc 30.77 mA/cm2, and FF 12.68%.
Figure 4 illustrates the effect of ETL thickness and performance on ab-layer at 850 nm. When the ETL thickness is 20 nm, we get the best performance on the simulated device with the highest PCE of 24%, which is increased by 0.02% efficiency with FF of 12.68%, Voc of 6.20V, and Jsc of 30.77 mA/cm2.
From Fig. 5. Shows the impact on the HTL and the device performance at 850 nm Ab-layer. When the thickness of the Ab-layer is at 850nm, we reach the maximum PCE 24.22% at 10 nm thickness of HTL with FF of 12.68%, Voc of 6.20V, Jsc of 30.77 mA/cm2.
In this simulation, the Nt of ab layered varied between 1012 cm−3 and 1018 cm−3 to find the best absorber thickness to find the variation in PCE, as shown in the Fig. 6,7,8 for the simulated device. PCE at other parameters of the simulated solar cell decreased as the absorber layer's Nt increased. As the defect density decreased, the efficiency stabilized at a certain point in this work, with the device performing well at 1016 cm3 (Nt) of absorber layer. The device performs best at 1018cm−3 and 1020cm−3 for ETL and HTL, respectively.
Sn-based PSC has a tunable band gap ranging from 1.3eV to 2.15eV. (vedanayakam, mandadapu.,2017). In this simulation, the bandgap of the optimized solar cell ranged from 1.2eV to 2.0eV for the best ab-layer to determine the variation in efficiency and other parameters. As shown in the figure 9, as the bandgap increased, PCE, FF, and Jsc decreased slightly while Voc increased. Jsc decreased as the bandgap increased, owing to less electron generation. After several simulations, the device was tested at 1.4eV. Similarly, we optimised the bandgap of ETL and HTL until we found the best performance of CuI at 2.8 eV and ZnOS at 2.4eV after several attempts. Figure 10 depicts the external quantum efficiency curve for the device's best absorber layer.
1D SCAPS was used in this study to investigate the optimized and simulated behaviors of the Sn-based PSC with ETL as ZnOS and HTL as CuI configuration. The working temperature 340 k for this simulation study at standard illumination of Air mass at 1.5G, the perovskite layer from150 nm to 1050 nm and the optimum layer range for HTL and ETL as 10-50 nm respectively both layers. The best layer thickness ranges from ZnOS are 20 nm and CuI is 10 nm respectively. The best defect density is performed at 1016cm-3 for this simulated device. The band gap of ab-layer HTL, ETL were to change from after several simulation 1.4eV, 2.4 eV, 2.8 eV, respectively. The device performed well and good at when Nt of the ab-layer 1016cm−3 with bandgap 1.4eV. When the optimized input parameter values are considered, the highest efficiency achieved is 24.22% (FF of 12.68%, Voc of 6.20V, Jsc of 30.77 mA/cm2). When we use CuI as the hole transport layer and ZnOS as the electron transport layer in a FASnI3-based solar cell, we get the best results, and CuI and ZnOS are the best replacements for Spiro-OMeTAD and TiO2. The simulated result stands for only replacement materials for FAPbI3, Spiro-OMeTAD and TiO2 because Pb based material had high toxicity for that reason we use Sn based ab-layer in this work. Spiro-OMeTAD and TiO2 are too costly for that reason in this work we used lost cost CuI, ZnOS as HTL and ETL respectively.
PSC- Perovskite solar cell
PV- Photovoltaic technology
SCAPS- Solar cell Capacitance simulation
FASnI3 – Formamidinium tin iodide
MASnI3- Methylammonium tin iodide
ZnOS- Zinc oxysulphide
FA- Formamidinium
Cs- Cesium
MA- Methylammonium
Sn- Tin
Pb-Lead
Cu- Copper
Copper iodide- CuI
ETL- Electron transport layer
HTL- Hole transport layer
TiO2-Titanium Oxide
Spiro-OMeTAD - 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9
Voc- Voltage output circuit (Voc),
Jsc- Current density
FF- Fill factor
PCE- Power conversion Efficiency
Nt- Donor
NA- Acceptor
Table.1 [3,10,15,20,21,22]
Material property |
ZnOS |
FASnI3 |
CuI |
Thickness ‘t’(nm) |
Varied |
Varied |
Varied |
Bandgap ‘Eg’ (eV) |
2.8 |
1.4 |
2.6 |
Electron affinity ‘χ’ (eV) |
3.9 |
3.52 |
3.9 |
Relative Dielectric permittivity ‘εr’ |
3 |
8.2 |
4 |
CB effectivite density of state ‘Nc’ (cm-3) |
1E+20 |
1.0E+18 |
1E+21 |
VB effective density of state ‘Nc’ (cm-3) |
1E+20 |
1.0E+18 |
2E+20 |
Electron mobility ‘μn’ (cm2/V.s) |
1E-4 |
22 |
0.01 |
Hole mobility ‘μp’ (cm2/V.s) |
1E-4 |
22 |
0.01 |
Donor concentration ‘ND’(cm-3) |
1E+7 |
0 |
1E+20 |
Acceptor concentration ‘NA’(cm-3) |
1E+7 |
7.0E+16 |
_ |
Defect density ‘Nt’ (cm-3) |
- |
2.0E+15 |
_ |
Table.2: Parameters for back and front contact. [23,24,25]
Parameters |
Back contact |
Front contact |
Surface recombination velocity of electrons (cm/s) |
1.00E+7 |
1.000E+5 |
Surface recombination velocity of holes (cm/s) |
1.000E+5 |
1.000E+7 |
Metal work function (eV) |
5.144 |
4.43 |
Majority carrier barrier height relative to Ef (eV) |
-0.0444 |
-0.0600 |
Majority carrier barrier height relative to Ev (eV) |
-0.0000 |
-0.0028 |