Solar Cell Performance Parameters Research Articles

Design of experiments with the support of machine learning for process parameter optimization of all‐small‐molecule organic solar cells

AbstractTraditionally, squaraine dyes have been studied and employed in biomedical research due to their excellent optical properties, and the molecules are being adopted in different research fields such as organic solar cells. In this study, we investigate correlations between solar cell performance and processing parameters of all‐small‐molecule bulk heterojunction solar cells comprising squaraine (SQ) as electron donor (D) and non‐fullerene small molecules (e.g., ITIC) as electron acceptor (A) with the help of machine learning (ML) and design of experiment (DoE) methods. Among the five predictive ML models tested with the selected parameters, the eXtreme gradient boosting model shows the satisfactory results with quite high coefficient of determination of 0.999 and 0.997 in training and testing sets, respectively. By measuring the contribution of each input variable to solar cell efficiency, four process parameters, that is, the total concentration, the ratio of D/A, the rotational speed of spin coating, and the annealing temperature, are found to be the key features strongly correlated to solar cell efficiency. From contour plots in DoE, the highest solar cell efficiency of approximately 5% can be predicted under the conditions of 15 mg mL−1 in solution concentration, a 1:2 mix ratio of D and A, rotational speeds ranging from 800 to 900 rpm, and annealing temperatures within 100–110°C. Using the suggested parameter conditions, we fabricated solar cells, achieving a quite high efficiency of approximately 4%. Besides the global optimization conditions, we also employ the solvent vapor annealing combination to the thermal annealing to facilitate further mobilization of molecules and more optimized microstructure of bulk heterojunction films, resulting in a further enhancement in solar cell efficiency of more than 20%.

A theoretical investigation into the impact of temperature and band gap variation of La2NiMnO6 oxide double perovskite nanostructures on the performance of La2NiMnO6/MASnI3 based hybrid solar cells

The study aimed at simulating a model of bilayer La2NiMnO6/MASnI3 hybrid perovskite solar cell having a potential benefit of better stability at higher operating temperature with higher band gap of LNMO. This numerical analysis of La2NiMnO6/MASnI3 based hybrid solar cell performance parameters has been carried out as a function of temperature and optical band gap (Eg) of La2NiMnO6 (LNMO). The analysis reveals that the fill factor of solar cells operated at room temperature has not been affected too much on varying Eg of LNMO and decreases non-linearly with increasing operating temperature. The open circuit voltage of solar cells operated at room temperature increases with increasing Eg of LNMO and drops linearly with increasing operating temperature. The short-circuit current density (JSC) increases non-linearly at different rates with increasing the operating temperature. The value of dη/dT increases up to a critical temperature (Tc) and then decreases in the solar cells comprised with higher Eg of LNMO (Eg ∼ 1.50 eV–1.60 eV). The Tc value was shifted towards higher operating temperature in the higher Eg of LNMO (Eg ≥ 1.50 eV), enabling more stable solar cell at higher operating temperature.

Comparative examination of both spectral properties and hybrid solar cell application of 2,4,6-trimethoxyphenoxy substituted phthalocyanine dyes

In this study, novel octa 2,4,6-trimethoxyphenoxy substituted phthalocyanines, and tetra chloro and tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines were synthesized, characterized, examined their spectral properties comparatively and investigated of hybrid solar cell application of them. The spectral characterizations can be performed for all phthalocyanine compounds, solar cell application was only possible for tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines, the others phthalocyanines not due to their low yield.Solar cell properties of the tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted phthalocyanines were studied using the ITO/ZnO/C60/ P3HT /LiF/Al structure. In order to improve and compare performance parameters of the poly(3-hexylthiophene) (P3HT) based solar cells, the tetra chloro tetra 2,4,6-trimethoxyphenoxy substituted H2Pc (2), Co(II)Pc (3) and Ni(II)Pc (4) compounds were incorporated individually into the solar cell structure between ZnO and C60 layers in which amorphous ZnO nanoparticles serves as electron transfer layer. Solar cell performance parameters such as short circuit current density (JSC), open circuit voltage (VOC), fill factor (FF) and power conversion efficiency (η) were studied as comparison parameters. Incorporation of Ni(II)Pc (4) into the reference structure between ZnO and C60 caused an increase 23.4 % in Jsc and 4.4 % in η whereas incorporation of Co(II)Pc (3) layer into the reference structure caused an increase 135.0 % in Jsc and 107.0 % in η under an illumination of 100 mW/cm2 with an AM 1.5G solar simulator. The best JSC and η (%) values were obtained for P3HT based solar cells with Co(II)Pc (3) interlayer.

Optimum Solar Cell Power Conversion Efficiency-Based Patterned Planar Solar Surface Morphology with Various Solar Cell Absorber Structures

This paper simulated the optimum solar cell power conversion efficiency-based planar solar surface morphology with various solar cell absorber structures. The spectral light intensity, reflected, absorbed, and transmission coefficients versus wavelength band spectrum varied from 300[Formula: see text]nm to 1300[Formula: see text]nm through the visible to near-infrared regions. The optimum solar cell performance parameters or key parameters are studied with different solar cell structure designs based on different surface contact and back contact layers. Cumulative generation current, cumulative electron–hole pair generation rate and electron–hole pair generation rate are clarified versus substrate depth for various solar cell structure designs. The absorbed current in substrate is optimized for various solar cell structure designs. Maximum power voltage and current are also optimized for the proposed solar cell structure design. The effective solar cell power efficiency is also demonstrated based on the optimized maximum power current and maximum power voltage.

An analysis comparing the performance of lead and tin halides organic Perovskite Solar Cells and numerical simulation with SCAPS

The scientific community focused on finding environmentally safe alternative metal halides to address the instability and toxicity associated with lead perovskite materials. These alternatives are supposed to replace lead halides without altering the distinctive properties of lead perovskite materials. Additionally, they should contribute to producing longer-lasting and stable perovskite in solar cells. This research presents a practical investigation of using tin- and lead-based composites in perovskite iodide solar cells with Titanium dioxide (TiO2) and Copper oxide (CuO) as electron transport materials (ETM) and hole transport materials (HTM), respectively. The performance parameters of the perovskite solar cells (PSCs) are compared with those of lead-based and lead-free PSCs with the same charge transport layers of ETM and HTM, as well as compare the practical results with the software results of Solar Cell Capacitance Simulation (SCAPS) package. In this study, the performance of PSCs with an absorption layer ((CH3NH3PbI3)t/(CH3NH3SnI3)1-t) was examined. The thickness of the perovskite layer is represented by (t), which can take the values(t = 1, 0.5, or 0) μm. The results of the laboratory study were compared to the performance of PSCs based on numerical analysis of SCAPS modeling. PSCs were prepared with a configuration structure (FTO/compact TiO2/(CH3NH3PbI3)t/(CH3NH3SnI3)1-t/CuO/Cu-electrode). A tetragonal phase was obtained for perovskite materials CH3NH3PbI3 and CH3NH3SnI3 with a direct optical energy gap estimated at (1.55 and 1.35) eV, respectively. The l-V curve of the prepared PSCs was studied, and the performance of the solar cells was examined under a light intensity of 100 mW/cm2. The power conversion efficiency, PCE, of the prepared solar cells, was (PCE = 2.9, 3.11, or 0.5) at (t = 1, 0.5, or 0)μm, respectively. A comparative analysis was also performed between the empirical performance of the manufactured PSCs and the theoretical results acquired by the SCAPS package software.

Thymus schimperi Ronniger plant flower extract dye-sensitized solar cells

The demand for energy is greatly increasing due to the world’s population growth and technological advancement. Natural dye-sensitized solar cells are attracting research as an alternative and renewable energy source due to their simple preparation technique, availability, cost effectiveness and environmental friendliness. In the present work, we have successfully fabricated dye-sensitized solar cells (DSSCs) from Thymus schimperi Ronniger plant flowers for the first time. The solvents used for extraction of the flower dye were deionized water and its mixture with ethanol. The T. schimperi Ronniger flower extract dye solutions and sensitized photoanodes were characterized by Fourier transform infrared and ultraviolet–visible techniques. The crystallinity of TiO2 films was analyzed by x-ray diffraction, and the films showed pure anatase phase behavior. The photoelectrochemical solar cell performance parameters, such as short circuit current density, open circuit voltage, fill factor and efficiency, were evaluated from current density–voltage measurements using a Keithley 2450 source meter. DSSCs sensitized with dye solution extracted by a mixture of water and ethanol showed better performance (1.37%) than those sensitized with dye solution extracted by deionized water alone (1.02%).

Measurement of information content of Perovskite solar cell’s synthesis descriptors related to performance parameters

AbstractPerovskite solar cells (PSC) are formed by different layers composed of thin films of various materials, in which the properties of every thin layer affect the performance of the cell. The identification of those most relevant properties (or descriptors) has a significant impact on the optimization and cost reduction of the Perovskite solar cell. This relevance is typically evaluated by adjusting a model using subsets of features, but in the present work, we propose to use the mutual information measure to quantify the statistical association between input descriptors and Perovskite solar cell performance parameters (Voc, Jsc, FF, PCE). As a result, it is found that ion X is the factor that most impacts the performance of the solar cell. On the other hand, variables such as band gap, Perovskite layer thickness, and A and B ions are also important. In this work, we identify some of the most important factors affecting Perovskite solar cells’ performance, and it could help to improve the efficiency of Perovskite solar cells. In addition, this proposed method could also be applied to other types of functional coatings, thin films, and surfaces.

Energy-Level Interpretation of Carbazole Derivatives in Self-Assembling Monolayer.

Energy-level alignment is a crucial factor in the performance of thin-film devices, such as organic light-emitting diodes and photovoltaics. One way to adjust these energy levels is through chemical modification of the molecules involved. However, this approach may lead to unintended changes in the optical and/or electrical properties of the compound. An alternative method for energy-level adjustment at the interface is the use of self-assembling monolayers (SAMs). Initially, SAMs with passive spacers were employed, creating a surface dipole moment that altered the work function (WF) of the electrode. However, recent advancements have led to the synthesis of SAM molecules with active spacers. This development necessitates considering not only the modification of the electrode's WF but also the ionization energy (IE) of the molecule itself. To measure both the IE of SAM molecules and their impact on the electrode's WF, a relatively simple method is photo-electric emission spectroscopy. Solar cell performance parameters have a higher correlation coefficient with the ionization energy of SAM molecules with carbazole derivatives as spacers (up to 0.97) than the work function of the modified electrode (up to 0.88). Consequently, SAMs consisting of molecules with active spacers can be viewed as hole transport layers rather than interface layers.

Exploring the potential of tin-based perovskite-silicon tandem solar cells through numerical analysis: A pathway to sustainable energy innovation

“Necessity is the mother of invention.” The global imperative to transition from fossil fuels to renewable energy sources, driven by the pressing issue of climate change, highlights the significance of advancing solar energy technologies. While single junction solar cells have reached a peak efficiency of approximately 31 %, the pursuit of higher efficiency has led to the exploration of tandem solar cell architectures, including perovskite-silicon and all-perovskite configurations. However, the widespread use of lead in perovskite structures raises environmental and health concerns. In response to these challenges, this study proposes a novel approach by integrating a tin-based wide bandgap absorber layer with a silicon HIT solar cell (Heterojunction with Intrinsic Layer). The investigation consists of an extensive exploration of six different carrier transport layers (CTL) for the top perovskite layer, considering variations in thickness and defect density. A comprehensive analysis of charge carrier dynamics within the device is conducted to understand the role of defect density in influencing solar cell performance parameters. Simulation results show that the overall tandem device gives an encouraging PCE of 32.12 % in 2 T configuration due to its excellent high value of current density matching 17.63 mA/cm2 and open-circuit voltage of 2.19V. We sincerely hope that our work will open new avenues in the field of Solar Photovoltaics paving the way for future innovations.

Rubidium based new lead free high performance perovskite solar cells with SnS2 as an electron transport layer

Lead-free perovskite-based solar cells has acquired rapid and expanding attention due to removing hazardous lead from perovskite materials. The major goal of this work is to supplement the research progress by doing a comparative analysis of lead-free perovskite-based solar cells using DFT and a numerical simulation method with the solar cell capacitance simulator-SCAPS-1D. At first, the bandgap and all optical performance were calculated via DFT then these data were applied SCAPS-1D simulator. Next design and optimized all solar cell performance parameters and compare of lead-free perovskite of RbSnCl3 and traditional perovskite RbPbBr3 solar cell with SnS2 as a high-bandgap chalcogenide electron transport layer (ETL) through SCAPS-1D. The effect of absorber and electron transport layer (ETL) thickness, doping concentration, defect density, interface defect density and temperature impact on solar cell efficiency has been comprehensively explored and compared. The proposed heterostructure of Al/FTO/SnS2/(RbPbBr3 and RbSnCl3)/Au shows that the PCE over 29.75% and 33.61% obtained with VOC of 0.978 and 0.825 V, Jsc of 34.58 and 51.44 mAcm−2, and FF of 87.91 and 79.19% for RbPbBr3 and RbSnCl3 absorber, respectively. These detailed findings revealed that high-performance lead-free perovskite solar cells can be achieved in a near future.

Comment on "Improving the efficiency of a CIGS solar cell to above 31% with Sb2S3 as a new BSF: a numerical simulation approach by SCAPS-1D" by M. F. Rahman and S. Goumri-Said et al., RSC Adv., 2024, 14, 1924.

It was reported in early 2024 that a single-junction 1.1 eV bandgap copper indium gallium selenide (CIGS) solar cell can achieve actual power conversion efficiency up to 40.70%, open circuit voltage up to 1.330 V, and fill factor up to 90.55% at 300 K when the solar cell is irradiated by the air mass 1.5 global (AM1.5G) solar spectrum (M. F. Rahman et al., RSC Adv., 2024, 14, 1924-1938). These simulated solar cell performance parameters exceed the ideal detailed balance-limiting power conversion efficiency, open circuit voltage, and fill factor of a 1.1 eV bandgap single-junction solar cell.

State-of-the-art with the prospects of cobalt-based metal-organic frameworks for solar cell applications

The characteristics of metal–organic framework (MOF) composites make them the most significant materials for energy conversion applications. MOFs are hybrid molecular frameworks synthesized using metal ions like Copper, Cobalt, Zinc, Nickel, etc and organic ligands such as BTC, NDC, etc. To meet and fulfill futuristic energy demands and needs, it is feasible to expand cost-effective energy conversion solar cell devices using MOF materials, therefore in the present work, the Cobalt-based MOFs (Co-MOF) are synthesized by coordinating Cobalt nitrate and 1,3,5 Benzene tricarboxylic acid (BTC or Trimesic acid) ligand using the Solvothermal method. To study the physiochemical properties of synthesized Co-BTC MOFs, these have gone through a variety of characterization processes where the structural exploration unveils that the intensity of the dominant peak obtained at 18.7° gradually decreases with a decrease in the concentration of trimesic acid ligand. First and second weight losses, corresponding to release of the solvent molecules and breakdown of the frameworks, respectively, were detected by thermogravimetric analysis (TGA) measurements. In the FTIR spectra, metal-oxide, modified benzene, carboxylic, and hydroxyl groups with different modes of vibrations are observed. Analysis of surface morphology demonstrated creation of rod-like geometry to the synthesized materials, whereas elemental studies inveterate effective formation of the Co-BTC MOFs. Additionally, the optimized Co-BTC MOF is applied as a potential interfacial layer in solar cells and the outcome implies that the device designed with 10 Co-BTC LBL cycle evolutions provided relatively desirable solar cell performance parameters. The present findings recommended that material progression is necessary to develop cost-effective and high-performance MOF-based solar cell devices.

Design and Numerical Analysis of Thin Film Solar Cells Based on Cu₂ZnSn (SₓSe₁₋ₓ)₄ with SnO₂ TCO and ZnS Buffer

Due to their earth-abundance, direct and adjustable bandgap in the range of visible light, and lower fabrication cost on large areas, Cu2ZnSn(SxSe1-x)4 semiconductors, commonly known as kesterite, are gaining recognition as potential materials for affordable, environment‐friendly, and high‐efficiency thin‐film photovoltaics. In this work, we numerically investigated the performance parameters of a single-heterojunction solar cell using Cu2ZnSnS4 (CZTS) / Cu2ZnSnSe4 (CZTSe) absorber layer and ZnS buffer layer, with SnO2 transparent conducting oxide (TCO) under a range of operating conditions and cell parameters. Maximum efficiency of 20.68% was obtained for a 5.5 µm absorber layer with 0.01 µm ZnS buffer layer for Cu2ZnSnSe4 solar cell, and 22.86% was obtained for a 6 µm thick Cu2ZnSnS4 absorber layer with 0.03 µm ZnS layer at room temperature and standard irradiance. The increase of irradiance to thrice the standard value led to 1% and 5% increase in efficiency for CZTS and CZTSe cells, respectively. Efficiency increased by 39% and 6.6% when the front surface was textured at an angle of 90° for CZTS and CZTSe cells, respectively. The CZTS and CZTSe based solar cells with optimized thickness and 90° textured front surface with three times the standard irradiation, showed 25.59 % and 21.52 % efficiency with open circuit voltage 1045 mV and 579.4 mV and short circuit current 85.84 mA/cm2 and 140.7 mA/cm2, respectively. The proposed architecture in this study will help produce next-generation solar cells that are both economical and energy-efficient.

Optimizing the performance of Cs2AgBiBr6 based solar cell through modification of electron and hole transport layers

This work investigates the potential of Cs2AgBiBr6 as an absorber layer for solar cell applications and explores ways to advance the PV performance of cells by studying different electron transport layers (ETLs) and hole transport layers (HTLs). The energy band diagrams of the Cs2AgBiBr6 based cell are analyzed with different ETLs and HTLs to illustrate how electrons and holes flow within the cell. Specifically, one of the proposed cells substitutes TiO2 with chlorine passivated tin oxide (Cl@SnO2), while the other uses phenyl-C60 -butyric acid methyl ester on tin oxide (C60 -SnO2) as the ETL. The PV characteristics of the Cs2AgBiBr6-based solar cell is evaluated using SCAPS 1D. The PV performance parameters of Cs2AgBiBr6-based solar cells has been analyzed in search of optimum thickness of Cs2AgBiBr6 layer. Subsequently, the impact of bulk defect density in Cs2AgBiBr6 layer at the obtained optimum thickness i.e., 611 nm has also been explored. C60-SnO2 is found to have higher electron mobility, work function, and stability than Cl@SnO2, making it a better choice for the ETL. The resulting PV parameters for the cell Cl@SnO2/CS2AgBiBr6/Me4PACz are: VOC - 1.527 V, JSC - 10.42 mA/cm2, FF − 75.66%, and PCE - 12.08%. While the cell SnO2-C60/Cs2AgBiBr6/Me4PACz delivers PV parameters VOC- 1.53 V, JSC- 12.81 mA/cm2, FF - 79.15%, and PCE - 13.43%.

SCAPS device simulation study of formamidinium Tin-Based perovskite solar Cells: Investigating the influence of absorber parameters and transport layers on device performance

The use of tin-based perovskite has gained popularity as an alternative to toxic lead-based perovskite in solar cells. Despite the wider absorption of the lead-free perovskite material known as CH3NH3SnI3, it is prone to temperature instability, which limits its applicability. Compared to CH3NH3SnI3, the absorber comprising FASnI3 (HC(NH2)2SnI3) exhibits greater temperature stability and a wider band gap of 1.41 eV. This study employs SCAPS to simulate FASnI3-based solar cells, examining how altering the absorber parameters, including thickness, doping concentration, and defect density, affects device performance. Additionally, we investigate the influence of modifying the conduction band offset (CBO) and valence band offset (VBO), as well as the thickness and doping concentration of the electron and hole transport layers (ETL and HTL). Furthermore, the impact of interface defect density, series and shunt resistance, and the temperature dependency of the device performance are analyzed. The original design was founded on an experiment that achieved a PCE of 1.75%. However, the presented parametric study led to improvements in the intended solar cell's performance parameters. Specifically, the cell's short-circuit current density (JSC) increased to 26.9 mA/cm2, the fill factor (FF) reached 74.22 %, the open-circuit voltage (VOC) rose to 0.907 V, and the power conversion efficiency (PCE) reached 18.11% at room temperature. Additionally, at a lower temperature of 280 K, the PCE further increased to 19.19%. The findings provide valuable insights into the efficiency, stability, and optimization of FASnI3-based solar cells for renewable energy applications.

Effect of temperature on the performance of Cesium formamidinium lead mixed halide perovskite solar cells

For the practical application of the Cesium formamidinium lead mixed halide (FA0.83Cs0·17PbI3-xBrx) perovskite solar cells, the impact of the operating temperature (T) on the solar cell performance parameters (Jsc, Voc, fill factor FF, and η) was investigated using SCAPS-1D simulation. The Br content varied from 0.5 to 2.5. The Jsc increased linearly with a rise in T, but on contrary, the Voc decreased linearly. Though the temperature coefficient of Jsc was enhanced with the rise of Br content. The lowest temperature coefficient of Voc was obtained for x = 2.5 for the cell of the two defect layers. The cells with a Br content of 0.5 shows the highest degradation due to Voc loss. The η of the cell without defect and with one defect layer slightly improved with rising the temperature to 400 K. This study suggests that the selection of the absorbing layer enormously depends on environmental conditions.

Design of an eco-friendly perovskite Au/NiO/FASnI3/ZnO0.25S0.75/FTO, device structure for solar cell applications using SCAPS-1D

Formamidinium Tin Iodide (FASnI3) based perovskite solar cells (PSC) have captured the interest of scientific community because of wide bandgap and good thermal stability, but limited power conversion efficiency (PCE) restricts their extensive adaptation. Here, we present the design of a FASnI3 active layer-based PSC with Nickel oxide (NiO) as Hole Transport Layer (HTL) & Zinc Oxy-Sulphide (ZnO0.25S0.75) as the Electron Transport Layer (ETL). The proposed Au/NiO/FASnI3/ZnO0.25S0.75/FTO, device structure is investigated using SCAPS-1D solar cell capacitance simulator. The performance parameters of proposed solar cells device structure are investigated with variations in active layer (FASnI3) thickness, defect density & doping concentration; and variations of NiO HTL & ZnO0.25S0.75 ETL thickness, electron affinity & doping concentration to obtain higher performance. Moreover, the influence of series & shunt resistance, and temperature on the performance parameters of proposed solar cell device structure is inspected. The proposed Au/NiO/FASnI3/ZnO0.25S0.75/FTO, device structure revealed excellent solar cell performance parameters such as low short-circuit current density (Jsc) of ∼28.35 mA/cm2, high Fill Factor (FF) of ∼89.64%, reasonable open-circuit voltage (Voc) of ∼1.2419 V, & admirable PCE of ∼31.57%, suitable for lead-free and eco-friendly solar cell device applications.

A comprehensive photovoltaic study on tungsten disulfide (WS2) buffer layer based CdTe solar cell

Transition metal di-chalcogenides (TMCDs)-Tungsten disulfide (WS2) exhibit excellent optoelectronic properties such as suitable bandgap, high absorption coefficient, good conductivity, high carrier mobility, etc. to be used as a photovoltaic material for thin-film solar cells. In the present work, we have replaced the traditional buffer CdS and ITO/ZnO window layer in CdTe solar cells with the non-toxic, earth-abundant WS2 buffer and SnO2 window layer, respectively. The SCAPS-1D solar simulator is used to investigate the potentiality of WS2 as buffer material in CdTe solar cells. This numerical study provides a comparison of the performances between the proposed structure: SnO2/WS2/CdTe/Au and the baseline structure: ITO/ZnO/CdS/CdTe/Au. The impacts of the charge carrier generation rate, spectral response, current-voltage characteristics, bulk defect density, defect density at buffer/absorber interface, operating temperature, and capacitance-voltage characteristics on the solar cell performance parameters have also been analyzed. The tolerance level of defect density in WS2 bulk and WS2/CdTe interface are found to be 1017 cm−3 and 1012 cm−3, respectively. The temperature study reveals the poor structural robustness and thermal stability of the proposed cell. The conversion efficiency of the proposed cell has found to be 20.55% at the optimized device structure. Nevertheles, these findings may provide an insight to fabricate viable, environment friendly, and inexpensive CdTe thin-film solar cells.

Fluorinated carbon nanotubes as nonvolatile additive to the active layer of polymer/fullerene solar cells

Highly dispersed fluorinated SWCNTs of submicron length were prepared, characterized and tested as nonvolatile additive to the active layer of polymer/fullerene organic solar cells. Two types of initial SWCNT materials – TUBALL® (OCSiAl) and Super purified plasma tubes (Nanointegris Inc.) – were used. The absence of big CNT aggregates was revealed by atomic force microscopy. The absence of metallic SWCNTs is confirmed by optical spectra of fluorinated SWCNT dispersions. Reproducible increase of the main performance parameters of solar cells (short circuit current, open circuit voltage, fill factor and power conversion efficiency) was obtained upon admixing a small amount of fluorinated SWCNTs (less than 1% weight) into the polymer/fullerene active layer, with either P3HT or PCDTBT donor and either PC60BM or PC70BM acceptor for both direct and inverted device architectures. Since effective charge mobility did not change upon fluorinated SWCNT admixture, the improvement of solar cell performance is not related to SWCNT-induced modification of the electronic structure of the active layer components or charge transfer via fluorinated SWCNTs. Presumably, the origin of this improvements is geometric optimization of the active layer morphology (improving connectivity of donor and acceptor domains) by fluorinated SWCNTs due to their high aspect ratio.

Analysis of variation in recombination characteristics due to light and heat in industrial silicon solar cells

This work presents a comprehensive analysis of the variation in performance parameters of monocrystalline and multicrystalline silicon solar cells when subjected to illumination at elevated temperature. Higher degradation and better regeneration in performance parameters namely open circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) are observed for monocrystalline solar cells. Suns-VOC measurement clearly indicate that the recombination current densities within the space charge region (J02) and rest of the solar cells (J01) together play an important role in light and elevated temperature induced degradation (LeTID) and subsequent regeneration characteristics. During the degradation phase, both J01 and J02 changed significantly for monocrystalline and multicrystalline solar cells. During regeneration, even though J01 improved for both the types of solar cells, notable reduction in J02 was observed only for monocrystalline solar cells. FF loss analysis shows that the recombination in the space charge region is majorly responsible for degradation and regeneration in FF. In contrast to most of the previous studies, we report similar reduction in external quantum efficiency (EQE) at 984 nm, 877 nm and 658 nm and propose that the formation of defects related to LeTID are not only in the deep bulk, but are distributed throughout the bulk. Absence of any improvement in EQE after prolonged exposure to light and heat suggests that defect transformation and gettering are not sufficient enough to regenerate JSC in multicrystalline solar cells. EQE maps at 407 nm suggest that LeTID behavior of emitter is different from that of bulk.