Properties Of Solar Cells Research Articles

Efficient regulation of active layer morphology and interfacial charge-transfer process by porphyrin-based additive in organic solar cells

Active layer morphology and interfacial charge-transfer (CT) properties in organic solar cells (OSCs) greatly affect device performance but are difficult to control. Here, a porphyrin derivative meso- tetrakis(3,5-bis(trifluoromethyl)phenyl)porphyrin (TBTPP) is applied as additive in OSCs to tune the morphology and interfacial CT process of donor PM6 and acceptor Y6 blend. In combination with molecular dynamics (MD), density functional theory (DFT), and time-dependent DFT (TD-DFT), we systematically investigate the active layer morphology and interfacial properties of PM6/Y6 and PM6/Y6/TBTPP. The theoretical calculations confirm that TBTPP can significantly regulate active layer morphology and interfacial CT characteristics. The results decipher that blend PM6/Y6/TBTPP features much stronger intermolecular interactions than PM6/Y6 and more phase separation interfaces. Moreover, after adding TBTPP, the percentage of CT states increases from 53% to 73%, and the net charge-transferred amount of almost all CT states enlarges. Under the TBTPP-addition condition, the charge separation degree of 60% excitons is improved. This research demonstrates that the introduction of TBTPP is of great significance for developing high-performance OSCs because it possesses the dual efficacy of regulating morphology and simultaneously improving CT properties.

Study of electron paramagnetic resonance as a tool to discriminate between boron related defects in barium disilicide

Barium disilicide (BaSi2), composed of Earth-abundant and nontoxic elements, is a promising material for thin-film solar cells. The control of carrier type and carrier concentration by impurity doping is particularly important for the application of BaSi2 to solar cells. However, the presence of defects in semiconductors such as BaSi2 may have a significant impact on the electrical and optical properties of solar cells. In this study, we chose boron to act as a p-type impurity in BaSi2 and studied boron-related defects using the Quantum Espresso method with density functional theory. The formation energy of interstitial boron defects was found to be lower than that of boron in Si vacancy sites. The hyperfine coupling constants of 137Ba with antisite boron defects (BSi) are very localized and differ significantly from those of 137Ba with interstitial boron defects (Bi). This suggests that neutral BSi and Bi can be identified by electron paramagnetic resonance.

Effect of UV-Light Irradiation on Charge-Accumulation States in PTzBT Polymer Solar Cells

Ternary polymer solar cells based on a polymer PTzBT have received a lot of attention because their power conversion efficiency (PCE) and thermal stability have been greatly improved by adding a small amount of an oligomer ITIC. However, the charge-accumulation states of the PTzBT ternary polymer solar cells have not yet been completely clarified. Here, we report electron spin resonance (ESR) spectroscopy of the PTzBT ternary polymer solar cells to investigate the charge-accumulation states from a microscopic viewpoint with examining the effect of UV-light irradiation. We observed a slight increase in the ESR intensity of the PTzBT cells and layered film samples under simulated solar irradiation with a UV-cut filter. Multiple signals were observed in the PTzBT cells under solar irradiation when the UV-cut filter was removed. Interestingly, no decrease was observed in the ESR signal of ZnO under solar irradiation with the UV-cut filter, although holes in ZnO in the PTzBT cells are known to decrease under solar irradiation. These findings will contribute to a deep understanding of the material properties of polymer solar cells.

Interface Engineering at Sc2C MXene and Germanium Iodine Perovskite Interface: First-Principles Insights

In recent years, Ge-based halide perovskite has gained increasing attention due to its potential in the development of lead-free perovskite solar cells. Here, through first-principles calculations, we explored the possibilities to enhance the optoelectronic properties of Ge-based perovskites via interfacial engineering between germanium iodine perovskite and 2D scandium-carbide MXene with various termination groups including F, O, and OH. We first evaluated the relative stability of the material interfaces and found that MAI-terminated interfaces are energetically more favorable than the GeI2-terminated interfaces. The MAI/F interface exhibits a type-II band alignment that can promote the photogenerated electron-hole separation. Moreover, the work function of the heterostructures can be tuned from 2.60 to 4.45 eV via using various termination groups. Additionally, 2D Sc2C MXene can also significantly enhance the light absorption. These results indicate that the 2D MXene serves as one promising candidate for optimizing the properties of perovskite solar cells via interface engineering.

Investigating the Role of Cathode Buffer Layers Based on Zinc Oxide with Surface‐Rich Graded Fullerene Isomers in Tuning the Interfacial Properties of Organic Solar Cells

In organic solar cells (OSCs), improving the properties at the interface of the bulk heterojunction (BHJ) photoactive layer and the buffer layer is desired, but achieving a high‐quality interface between these two layers is inevitably challenging. Herein, a novel (PC61BM)‐doped zinc oxide, that is, a (PC61BM‐ZnO)DEZ hybrid thin film, is proposed for application as a cathode buffer layer (CBL) for OSCs based on both fullerene‐based acceptors and nonfullerene acceptors. These thin films require low annealing temperatures and can be deposited via a one‐step solution‐processable method using a hybrid precursor composed of PC61BM and diethylzinc solution (DEZ). The study reveals that the performance of devices with (PC61BM‐ZnO)DEZ hybrid thin films as a CBL exceeds that of devices with thin films of conventional ZnO as a CBL. Impedance analysis of the fabricated OSCs suggests improved charge collection efficiency in the devices with (PC61BM‐ZnO)DEZ thin film. Optical, electrical, morphological, and compositional characterizations of thin films used as CBLs confirm the presence of a PC61BM‐rich phase with traces of d‐C61 (fullerene dimer) at the surface of the hybrid (PC61BM‐ZnO)DEZ thin film. These phases help in tuning the interfacial properties by ensuring better coupling between the BHJ photoactive layer and the CBL.

Integration of thin n-type nc-Si:H layers in the window-multilayer stack of heterojunction solar cells

N-type nanocrystalline silicon (nc-Si:H(n)) layers are good candidates to improve current and transport properties in heterojunction solar cells. In this work, we perform thickness series alongside PH 3 doping series to unravel the desirable characteristics of nc-Si:H(n) along its growth direction. While increasing the PH 3 flow is necessary to improve the conductivity of the layer, we observe that too high flows lead to an amorphization of the first 10–15 nm of the layers. In consequence, either high crystallinity are reached at intermediate PH 3 flow, resulting in high doping at the n/TCO interface but a poorly doped nucleation zone, or the material becomes more amorphous at very high PH 3 flow, allowing a higher doping in the nucleation zone but a less efficient screening of the barrier with the TCO due to the lower crystallinity. To overcome this trade-off, we integrate a 2.5 nm a-Si:H(n) layer underneath the nc-Si:H(n) layer. We also report on the impact of higher ITO doping as well as on the beneficial effect of an additional SiO x capping not only to form a double anti-reflective coating (DARC), but also to improve contact properties. We observe that each of those three features can improve passivation and selectivity as well as reduce strongly the front contact resistivity ( ρ c ). Our best results are achieved by using a thin a-Si:H(n)/nc-Si:H(n) stack together with an IZrO/SiO x DARC, enabling front ρ c lower than 15 mΩ cm 2 and an efficiency of 23.7% on screen-printed 2 × 2 cm 2 solar cells. • Development of nc-Si :H(n) layers for front application. • Trade-off between nucleation zone and high crystallinity evidenced. • a-Si:H(n)/nc-Si:H(n) bilayer strategy allow for ρ c ¡ 15 mΩ cm 2 . • Decreases dependency upon TCO lateral conductivity. • Good passivation (pFF = 85%) and transparency maintained.

Photoelectric properties of solar cells based on pCdTe-nCdS and pCdTe-nCdSe heterostructures

In this paper, we study the photoelectric properties of pCdTe-nCdS and pCdTe-nCdSe-based film heterostructures. It is shown that the high value of the electron diffusion length in pCdTe slick (pellicle) is due to the presence of a built-in field in it. The shift in the photosensitivity maximum is explained by changes in the band gap of cadmium telluride. As shown, the accumulation coefficient increases with raising thickness of the wide-gap layer. It has been established that the short-wavelength edge of the photosensitivity of the pCdTe-nCdS structure begins to increase sharply at a photon energy of hv ≤ 2,3 eV, while the photosensitivity of the pCdTe-nCdSe structure already at a photon energy has a significant value ∼ 100 μA/mV.

Impact of end-group modifications and planarity on BDP-based non-fullerene acceptors for high-performance organic solar cells by using DFT approach.

With the aim to enhance the photovoltaic properties of organic solar cells (OSCs), seven new non-fullerene acceptors (K1-K7) have been designed by end-group modifications of benzo[2,1-b:3,4-b']bis(4H-dithieno[3,2-b:2',3'-d]pyrrole) (BDP)-based small molecule "MH" (which is taken as our reference R) using computational techniques. To investigate their various optoelectronic parameters, DFT studies were applied using the B3LYP functional at 6-31G (d, p) basis set. The measurement of molecular planarity parameter (MPP) and span of deviation from plane (SDP) confirmed the planar geometries of these structures resulting in enhanced conjugation. Frontier molecular orbital (FMO) and density of states (DOS) analyses confirmed shorter band gaps of K1-K7 as compared to R, which promotes charge transfer in them. Optical properties demonstrated that these compounds have absorption range from 692 to 711nm, quite better than the 684nm of reference R. Molecular electrostatic potential (MEP) and Mulliken' charge distribution analysis also revealed the presence of epic charge separation in these structures. K1-K7 showed enhanced LHE values as compared to R putting emphasis on their better abilities to produce charge carrier by absorption of light. Reorganization energies showed that all newly designed compound could have better rate of charge carrier mobility (except K4) than R. Calculations of open-circuit voltage (Voc) and fill factor (FF) revealed its highest values for K3 and K4. Among newly designed molecules, K3 showed betterment in all its investigated parameters, making it a strong candidate to get enhanced power conversion efficiencies of OSCs.

Highly Improved Efficiency and Stability of 2D Perovskite Solar Cells via Bifunctional Inorganic Salt KPF6 Modified NiOx Hole Transport Layer

In general, improving the electrical conductivity of bare NiO x film and alleviating the undesired energy level mismatch by interface engineering are operative to enhance the property of 2D perovskite solar cells (2D PSCs) based on NiO x . Herein, the NiO x /2D perovskite interface is modified by inorganic salt KPF6 to improve the interfacial contact and conductivity of NiO x . It is revealed that KPF6 not only improves the conductivity of NiO x through the formation of NiF coordination bond with NiO x by PF6‐ but also promotes the energy level matching between NiO x and the 2D perovskite layer. Thus, KPF6‐modified NiO x greatly enhances the extraction ability of hole carriers in 2D perovskite layers and improves the crystallinity of 2D perovskite films. Accordingly, the NiO x /KPF6‐based 2D PSCs attain an optimal power conversion efficiency (PCE) of 14.34%. Meanwhile, the KPF6 modified device without sealed maintains 93% of its original PCE for 600 h on a 60 °C hot plate filled with nitrogen and 72% after aging for 600 h with a humidity of 35 ± 10% in the atmosphere, respectively. This study demonstrates the effectiveness of using inorganic salts to modify NiO x hole transport layers to augment the optoelectronic properties and stability of 2D PSCs.

The properties of perovskite solar cells with novel MAPbBr3/CsPbBr3 double absorber

Perovskite solar cells (PSCs) based on CsPbBr3 have garnered considerable attention due to their high stability and all-inorganic components. Although thermal annealing is a conventional and effective method to improve the quality of CsPbBr3 films, property improvement strategies are still scarce, especially for the vapor deposition process. In this work, a MAPbBr3 layer is introduced at the TiO2 and CsPbBr3 interface to construct a double-absorber heterojunction structure. It is found that the cubic phase of CsPbBr3 is formed directly on the MAPbBr3 underlayer due to the epitaxial growth. Furthermore, the heterojunction formed at the MAPbBr3/CsPbBr3 interface contributes to the superior extraction of the light-generated carriers. A power conversion efficiency (PCE) of 6.53% is obtained for the PSC with a double-absorber design. Despite the thickness of the epitaxial layer being shrunken after annealing at 150 °C for 30 min, a PCE of 5.90% is achieved, indicating the high thermal stability of the double-absorber device. Our work provides a new insight into quality engineering for the perovskite deposited by the vapor deposition process.

Bandgap tuning and thermoelectric characteristics of Sc-based double halide perovskites K2ScAgZ6 (Z = Cl, Br, I) for solar cells applications

Using the full-potential linearized augmented plane wave plus local orbitals method within the frame work of density functional theory, the Sc-based double halide perovskites K2ScAgZ6 (Z = Cl, Br, I) are investigated for determining their physical properties. To investigate the structural and thermodynamic stability of these Sc-based double halide perovskites we calculate tolerance factor, formation energy, and phonon dispersion curve using GGA-PBEsol approximation. The calculated values of lattice parameters using GGA-PBEsol are found to be consistent with the available data. Subsequently, the Tran-Blaha modified Becke-Johnson (mBJ-LDA) potential is used for electronic properties. Implementation of TB-mBJ potential is clearly shows that K2ScAgZ6 have indirect bandgap, which is consistent with the literature. To evaluate these double perovskites and reveal their potential use in optical devices, several optical parameters are computed for an incident photon energy range of 0–8 eV. The BoltzTraP code is also employed to investigate temperature dependent electrical characteristic of these compounds in the temperature range of 200–600 K. Investigated halide double-perovskites have been shown to display excellent physical properties for solar cells and renewable energy device applications.

Numerical simulation and optimization of physical properties for high efficiency CuSbS2 thin film solar cells

Here we present numerical modeling of copper antimony sulfide (CuSbS2) solar cells to analyze the impact of several interrelated physical parameters of the absorber layer and absorber/buffer interface such as bulk vs interface defect density, energy band gap vs electron affinity of CuSbS2, absorber thickness vs acceptor density together with device shunt vs series resistance on the device efficiency. A benchmark simulation of the experimental CuSbS2 solar cell is initially performed in SCAPS-1D (Solar Cell Capacitance Simulator in one dimension) environment considering a suitable defect model, which gave an efficiency of 3.19 % comparable to the experimental value. After the systematic optimization of different materials properties and interface defect density, the power conversion efficiency is increased up to 10.71 % with a remarkable upgrade in open circuit voltage, photocurrent, and fill factor. A detailed analysis of heterojunction features such as built-in potential, depletion width, diffusion length, and carrier recombination was performed to understand the impact of the aforementioned physical parameters on the performance of this solar cell. The present results give an important guideline to find out the shortcomings of CuSbS2 solar cells, which in turn help the researchers for designing and feasible fabrication of more efficient CAS solar cells.

Cu2SnSe3 phase formation from different metallic and binary chalcogenides stacks using magnetron sputtering

Cu2SnSe3 (CTSe) is a polyvalent material that can be used as an absorber layer for thin film solar cells or as a starting layer for the synthesis of CZTSe or CZTSSe compounds. Obtaining CTSe single phase films with optimized properties for thin film solar cells is a difficult task. A systematic study using both metallic and binary chalcogenides precursors for the formation of the CTSe phase was not performed. The films consisting of four different stacks (Sn\\Cu, SnSe2\\Cu, Sn\\Cu2Se, and SnSe2\\Cu2Se) were prepared by magnetron sputtering on soda lime glass (SLG) and molybdenum (Mo) coated SLG substrates, followed by annealing at 550 °C under Sn + Se atmosphere. X-ray diffraction and Raman spectroscopy results indicated the formation of a single CTSe phase in most of the stacks deposited on both substrates. Scanning electron microscopy images showed compact surfaces with large grains in the films deposited on Mo substrate, while the films on SLG have more voids on their surfaces. The elemental analysis measured by energy dispersive spectroscopy revealed stoichiometric films on Mo, and copper and tin rich compositions on SLG substrates. The band gap values inferred by conventional spectroscopy are between 0.81 and 1.95 eV. It was found that the SnSe2\\Cu and Sn\\Cu2Se stacks are preferred for the formation of a single CTSe phase, with dense surface morphology, a stoichiometric composition, and an optimal absorber layer band gap. This study opens the way to comprehend the formation reactions during the selenization of metallic and binary chalcogenides precursors towards the optimization of kesterite absorber for photovoltaic device fabrication.

Determining the optical properties of solar cells using low cost scanners

This paper investigates the use of consumer flatbed scanners for the use of monitoring solar cell precursors. Two types of scanners are investigated a contact image scanner and scanners with more conventional optical setups. The contact image sensor is found to be more suitable as it does not require additional flat field calibration. The scanners’ ability to monitor variation in sample texture was investigated by monitoring the reflection of multi-crystalline and mono-crystalline textured wafers. For a baseline, a comparison was made to a high-end tool used in industry. Both good qualitative agreement and statistical correlation were achieved between the scanner and industry tool for the isotropic multi-crystalline wafers.

Unraveling the impact of graphene nanostructures passivation on the electrical properties of the perovskite solar cell

Herein, the impact of graphene nanoplatelets (GNPs) passivation on the performance of perovskites solar cells (PSCs) has been investigated using fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and temperature dependence capacitance vs. frequency (C-f-T) measurements. Devices passivated with GNPs exhibited improved performance compared to the un-passivated device. The photoluminescence (PL) intensity of passivated perovskites films amplified as compared to the un-passivated perovskites film. The PL lifetime associated with the bulk of the perovskite increased from 830 ps to 991 ps, and the lifetime corresponds to the surface recombination delayed from 30 ns to 38 ns, confirming the suppression of non-radiative recombination centers on perovskites surface. The EIS measurements reveal that the passivated devices have higher recombination resistance and lower charge transport resistance, further confirming the decrease of recombination losses and improvement in the charge transport across the perovskites/charge selective contact (CSC) interface. Moreover, the temperature-dependent EIS measurement shows that the charge carrier lifetime increased from 30 μs in the un-passivated device to 42 μs in the passivated device, whereas the activation energy reduced from 43 meV to 13 meV. The C-f-T spectra reveal that the low-frequency evolution of capacitance in passivated devices decreases indicating the decrease of charge accumulation at perovskites/CSC interface. Finally, the activation energy for the charging/discharging of trap states in passivated devices dropped to 89 meV compared to 104 meV in the un-passivated device, further confirming the decrease in interfacial trap depth via GNPs passivation.

Machine learning assisted prediction of charge transfer properties in organic solar cells by using morphology-related descriptors

Machine learning assisted prediction of charge transfer properties in organic solar cells by using morphology-related descriptors

Effects of electron- and hole-current hysteresis on trap characterization in organo-inorganic halide perovskite

Charge trap density and carrier mobility of perovskite materials are the critical properties of perovskite solar cells. The space charge limited current (SCLC) method, which measures a dark current–voltage (I-V) curve of a single-carrier device has found extensive use for studying the trap density and charge carrier mobility in perovskite materials. Herein, it was found that the electron- and hole-current in organo-lead perovskite-based single-carrier device undergoes significant hysteresis under forward and reverse scanning due to the mobile ions. In addition, it was also observed that measuring history has a detrimental effect on hysteresis resulting in possible overestimation or underestimation of the extracted electrical values from the SCLC measurement. In the forward/reverse scanning process, the mobile ionic defects enhance/shield the charge in the traps due to ionic charging/discharging, thereby increasing/reducing the interface barrier and net charge in the I-V scanning, which in turn affects the determination of transport properties of the carrier. These results raise quite a few doubts over the direct application of classical SCLC measurements for the accurate characterization of intrinsic transport properties of the mixed ionic-electronic perovskite.

(Invited, Digital Presentation) Photovoltaic Applications Using Energy Transfer Characteristics from Quantum Dots

Silicon-related materials are most commonly used in solar cells and become now an invaluable material. However, a reported maximum energy conversion efficiency of Si solar cell is close to reaching its theoretical limits. To further improve the cell performance and create new functions, it will become increasingly important to functionalize Si materials using nanostructures. One- and zero-dimensional Si nanostructures called Si nanowires (SiNWs) and Si quantum dots (Si QDs) are increasingly being used as new solar cell materials. Our group has shown that the conversion efficiency of solar cells can be increased by the non-radiation energy transfer (NRET) from Si QDs [1]. Recently, research has been developed on compound semiconductor QDs and perovskite QDs, and the conversion efficiency has been successfully increased [3-7].n-type SiNW arrays were fabricated by electroless etching and Bosch & nanoimprint lithography followed by CVD process. The CVD process was performed to form p-type Si layer for pn homojunction. Hybrid heterojunction cells of PEDOT:PSS and n-SiNWs were also fabricated. Passivation by ozone and hydrogen were applied to improve the solar cell properties [2]. After the cell fabrications, the solar cells were coated with Si QDs, CdZnS/ZnS QDs, CdZnSe/ZnS QDs and perovskite QDs. The fabrication methods and conditions of QDs have been reported elsewhere [1-7]Energy transfer effects such as NRET are new ways of increasing solar cell efficiency. To effectively use the NRET effect, the surface of Si QDs should be fully passivated by ligand molecules. The NRET process is a highly distance-dependent phenomenon, and its dependence on the length of the passivation ligands clearly showed this. NRET efficiency was increased by shortening the ligand length from 1-octadecene to 1-octene, resulting in higher JSC, ultimately providing higher energy conversion efficiency. The efficiency was increased about 1-2 % by adding SiQDs. We also observed the same effect for CdZnS/ZnS QDs, CdZnSe/ZnS QDs and perovskite CsPbCl3 QDs. In these cases, in addition to the NRET effect, the radiative energy transfer (RET) effect also contributes to the increase in conversion efficiency.

Influence of Silicon Dioxide-Titanium Dioxide Antireflective Electrosprayed Coatings on Multicrystalline Silicon Cells

This research work primarily focuses on enhancing the power conversion efficiency (PCE) of polycrystalline silicon solar cells by using a single-layer and a double-layered antireflection coating deposited through the electrospraying technique. The usage of titanium dioxide and silicon dioxide as antireflection coating materials has shown a significant increase in the optical and electrical properties of solar cells under open and controlled light sources. The sample with TiO2 as a base layer and SiO2 as the top layer (sample B-IV) exhibited a maximum PCE of 18.90% in direct sunlight and 21.19% in a neodymium setup with cell temperatures of 40°C and 52.1°C, respectively. Sample B-IV has also shown the lowest resistivity of 3.1 × 10−3 Ω·cm among the coated samples. Also, an increase of 11.6% light transmittance and a reduction of 9.6% light reflectance were exerted by sample B-IV. The results obtained from different analysis proves that TiO2/SiO2 was an appropriate antireflection coating material for enhancing the PCE of the polycrystalline silicon solar cell.

Size effect of gold nanoparticles on optical and electrical properties of plasmonic silicon solar cell

One of important tasks of the day is increasing the efficiency and decreasing the cost of the silicon solar cells. There is method of introducing of metal nanoparticles into solar cells to improve its absorption and reduce transmission as well as reflection coefficients. When metal nanoparticles are introduced into silicon solar cell, nanoplasmonic effect will occur. Nanoplasmonic effect lead to modification of light spectrum and generation of extra hot electrons. Nano-plasmonic effect strongly depends on size of nanoparticles. Therefore, in this paper, effect of gold nanoparticles size on properties of silicon solar cell has been studied by using simulation. Gold nanoparticles with sizes of 4 nm, 6 nm, 9 nm, 11 nm and 21 nm have been input into emitter region of silicon solar cell in order to use both of nanoplasmonic-electric and nanoplasmonic-optic effects for enhancing efficiency of silicon solar cell. Open circuit voltage didn't change when size of nanoparticles has been changed from 4 nm to 11 nm. It dropped by 0.017 V when size of nanoparticles was 21 nm. Short circuit current has been maximum 6.7 mA/cm2 at nanoparticle size of 11 nm and minimum 3.1 mA/cm2 at nanoparticle size of 21 nm. It has been found from obtained results that gold nanoparticle with size of 11 nm affected significantly on properties of silicon solar cell. Besides, thickness of silicon solar cell can be decreased without dropping of efficiency by introducing gold nanoparticles. Because, main part of photons is absorbed near to metal nanoparticles inputted region.