Properties Of Organic Solar Cells Research Articles

Optical and photovoltaic properties of organic solar cells versus bulk-heterojunction morphology

Optical and photovoltaic properties of organic solar cells versus bulk-heterojunction morphology

Tailoring of centric extent fullerene-free acceptors to improve photoelectric properties of organic solar cells: A computational approach

Non-fullerene acceptors have attracted considerable interest due to their superior performance in organic solar cells compared to fullerene acceptors. Using density functional theory (DFT) and its time-dependent approach, the optoelectronic properties of designed molecules have been evaluated. The designed molecules have a low band gap of 2.046–2.072 eV, which is significantly lower than reference 2.080 eV. The designed molecules exhibit lower excitation energy in both gaseous (1.830–1.855 eV) and solvent states (1.711–1.738 eV) compared to R values of 1.871 eV (gaseous) and 1.751 eV (solvent). Low reorganizational energies of electron (λe = 0.0044–0.0052 eV) and proton (λh = 0.2285–0.2343 eV) has been achieved in all designed molecules compared to reference (λe = 0.3437 eV, λh = 0.2361 eV). The designed molecules showed an increase in open circuit voltage (Voc), ranging from 1.60 to 1.73 eV, compared to reference value 1.59 eV. In addition, a significant charge shift at the HOMO (PM6)-LUMO (BB3) interface was observed.

Solution Sequential Deposition Pseudo-Planar Heterojunction: An Efficient Strategy for State-of-Art Organic Solar Cells.

Organic solar cells (OSCs) are considered as a promising new generation of clean energy. Bulk heterojunction (BHJ) structure has been widely employed in the active layer of efficient OSCs. However, precise regulation of morphology in BHJ is still challenging due to the competitive coupling between crystallization and phase separation. Recently, a novel pseudo-planar heterojunction (PPHJ) structure, prepared through solution sequential deposition, has attracted much attention. It is an easy-to-prepare structure in which the phase separation structures, interfaces, and molecular packing can be separately controlled. Employing PPHJ structure, the properties of OSCs, such as power conversion efficiency, stability, transparency, flexibility, and so on, are usually better than its BHJ counterpart. Hence, a comprehensive understanding of the film-forming process, morphology control, and device performance of PPHJ structure should be considered. In terms of the representative works about PPHJ, this review first introduces the fabrication process of active layers based on PPHJ structure. Second, the widely applied morphology control methods in PPHJ structure are summarized. Then, the influences of PPHJ structure on device performance and other property are reviewed, which largely expand its application. Finally, a brief prospect and development tendency of PPHJ devices are discussed with the consideration of their challenges.

Excitation Energy Transfer via Electron Transfer between a Semi‐Conducting Single Walled‐Carbon Nanotube and Encapsulated Zinc Porphyrin or Photovoltaic Application

AbstractIn this paper, the encapsulating effect of single molecule of zinc porphyrin (Zn−P) inside semiconducting single walled carbon nanotubes (NT17) on the stability and optoelectronic properties of organic solar cells is investigated, assuming that this nano‐hybrid system will serve as the active layer in solar cell device. Making use of density functional theory (DFT), we looked at the optoelectronic characteristics of the isolated Zn−P molecules as well as two different configurations of the hybrid system that has a single Zn−P molecule inserted into NT17 (Zn−P@NT17 and Zn−P2@NT17). The addition of a zinc atom at the core of a porphyrin molecule results in the emergence of novel electronic and chemical characteristics, leading to distinct behavior compared to a free‐base porphyrin. These distinctions hold substantial implications for a range of applications, encompassing catalysis, sensing, and energy conversion processes. According to the study's outcomes, a charge transfer (CT) between the Zn−P molecules and the NT17 nanotube caused the structure to remain stable, and assuming to the electronic and optical computations the CT in Zn−P@NT17 hybrid nanosystems has been identified, along with its orientation. The results show that type II heterojunctions on filled semiconducting carbon nanotubes are likely to make them a viable choice for charge and light transport in the active layer, which can help create filled NT‐based OSCs that are extremely efficient.

Rational design of promising candidates for photoactive layer in polymer solar cells: Insights from computation

AbstractThe design of organic solar cells, OSCs, requests a more efficient configuration of photoactive layers composed of p‐type (quinoxaline, Qx) and n‐type (naphthalene diimide, NDI) semiconductors that enable light harvesting along with a high‐power conversion efficiency. Here, Qx‐(phenyl or Ph) and NDI structures have been modulated using both electron withdrawing (EWG) and electron donating (EDG) groups such as −F, −NHCOCH3, −OCH3, −OH, −CHO, −COOCH3, −COOH, −CN, −SO3H, and −NO2, aiming to design an effective photoactive p‐n layer. The HOMO‐LUMO gap of Qx‐Ph can be tuned to the visible light spectrum by the addition of EWG in the Qx ring (decreasing the LUMO energy) and by EDG in the Ph ring (increasing the HOMO energy). The analyzed complexes show key electronic properties in organic solar cells with large power conversion efficiency. Descriptive data analysis suggests that the magnitude of the non‐covalent interactions in donor acceptor (D A) complexes is expected to play a role in the efficiency of OSCs. The results will contribute to a more effective design of the photoactive layer in OSCs.

Improved optoelectrical properties for organic solar cells by introducing silicon quantum dots via eco-friendly and simple process

In this study, we synthesized eco-friendly silicon quantum dots (SiQDs) with absorption ≤400 nm and light emission of 440 nm and 500–550 nm. SiQDs were introduced into ZnO (sol-gel), an electron transport layer (ETL) of organic solar cells (OSCs) with an inverted structure.The introduction of SiQDs led to a smoother and more uniform surface morphology of the ETL. SiQDs improved the carrier mobility of the device, and increased carrier transport by reducing carrier recombination and interfacial resistance. Furthermore, SiQDs were found to convert ultraviolet (UV) light to visible light via light conversion effect. They contributed to improved JSC and FF in OSCs, and improved the power conversion efficiency (PCE) from 14.48 % to 15.31 % for the PM6:BTP-eC9 device (JSC: 24.42 mA cm−2 to 24.87 mA cm−2, FF: 73.05 %–75.23 %) and from 15.43 % to 16.3 % for the PM6:L8-BO device (JSC: 23.37 mA cm−2 to 24.57 mA cm−2, FF: 75.95 %–76.77 %).SiQD-doped ZnO, with eco-friendly synthesized SiQDs, not only improved the efficiency with the ETL of OSCs, but also demonstrated good stability.

Fluorenyl-based polyurethane efficiently improves the flexibility and photovoltaic performance of organic solar cells

Introducing proper insulating polymer in the active layer can improve the photovoltaic and mechanical properties of organic solar cells. Here, we design and synthesize a polyurethane insulating material K-BA20 (or 50) containing PDMS and 2D aryl block 9,9-diphenyl-9H-fluorene (DPF). Isophorone diisocyanate (IPDI) is selected as the connection unit and hydrogen bond is introduced to reduce the chain slippage caused by excessive one-dimensional structure. This strategy can enhance the adhesion between components, which can successfully improve the photovoltaic performance and mechanical properties of the devices. When 5 and 15 wt% K-BA20 was introduced into the PM6:Y6-based system, the short-circuit current density (JSC) of 26.71 and 26.65 mA cm−2, and the power conversion efficiency (PCE) of 16.67% and 16.05% were obtained. More interestingly, the active layer introduced K-BA20 with low DPF ratio has good stretchable properties, while K-BA50 with high DPF ratio has more stable flexibility. The breaking elongation of the blend film with introducing 15 wt% K-BA20 was increased 3.2-fold, from 5.81% to 18.46%, and the PM6:Y6-based flexible devices after doping 5 wt% K-BA50 can still maintain half of the initial efficiency under 600 bending fatigues. Hence, this work shows that introducing K-BA20 (or 50) into PM6:Y6 -based devices can bring out a series of positive feedbacks in terms of charge recombination, crystallinity and molecular interaction. It can be seen that constructing new insulating polyurethane materials with rigid and flexible segments is an effective strategy for development of flexible organic solar cells.

An Approach Towards Low Energy Loss by End-capped Modification of A2–D–A1–D–A2-type Molecules for Tuning the Photovoltaic Properties of Organic Solar Cells

In this project, the study is focused on the substitution at determined sites of reference molecule (R) to enhance optoelectronic properties, which might affect the photovoltaic performance of organic solar cells. Herein, seven new molecules (M1 to M7) were designed by the modification of the terminal acceptors. The density functional theory was employed to explore optoelectronic properties. Majority of the molecules own exceptional optical properties than reference molecule, for instance, narrow bandgap, low excitation energy, lower binding energies, better oscillator strength and progressive light harvesting efficiency. The density of state, frontier molecular orbitals and transition density matrix diagrams indicated that the charge density transfer occurs from donor to acceptor. Moreover, charge transfer investigations of designed molecules with PTB7-Th complex were performed by analyzing the concentration of charge transfer over molecular orbitals, i.e., highest occupied to lowest unoccupied molecular orbitals. Thus, these computed molecules may be employed to develop efficient organic solar cell devices with promising photovoltaic prospects in the near future.

Organic Solar Cells: An Analysis of AC and DC Electrical Properties

In this paper, AC and DC electrical properties of organic solar cells based on P3HT:PCBM active layer have been investigated. The performance of such solar cell has demonstrated the efficiency of 2.31% corresponding with short-circuit current density of 6.08 mA ⋅ cm[Formula: see text], open circuit voltage of 0.64 V and fill factor of 60%. The equivalent circuit and the properties of the supposed interfaces between the layers in the P3HT:PCBM-based solar cell have been estimated. AC properties have demonstrated series capacitance increasing with increasing frequencies, which means series capacitance saves charges and parallel capacitance has decreased with increasing of frequency work as discharge part of charges stored in series capacitance. Also, equivalent series and parallel resistances have demonstrated a decrease from 7 [Formula: see text] and 120 k[Formula: see text] at low frequency to 1 [Formula: see text] and 43 k[Formula: see text] at high frequencies, respectively.

Exploration of charge transfer analysis and photovoltaics properties of A-D-A type non-fullerene phenazine based molecules to enhance the organic solar cell properties

To intensify the photovoltaic properties of organic solar cells, density functional theory (DFT) based computational techniques were implemented on six non-fullerene A-D-A type small molecules (N1–N6) modified from reference molecule (R) which consists of phenazine fused with 1,4- Dimethyl-4H-3,7-dithia-4-aza- cyclopenta [α] pentalene on both sides with one of its phenyl rings acting as the central donor unit, further attached with 2-(5,6-Difluoro-2-methylene-3-oxo-indan-1-ylidene)-malononitrile acceptor groups at terminal sites. All proposed compounds have a phenazine base modified with a variety of substituents at the terminals. Transition density matrix, density of states, frontier molecular orbitals, intramolecular charge transfer abilities and optoelectronic properties of these compounds were investigated using B3LYP/6-31G (d, p) and B3LYP/6-31G++ (d,p) level of theory. All six designed compounds exhibited a bathochromic sift in their λmax as compared to the R molecule. All designed molecules also have reduced band gap and smaller excitation energy than R. Among all, N6 exhibited highest λmax and lowest bandgap as compared to reference molecule indicating its promising photovoltaic properties. Decreased hole and electron reorganization energy in several of the suggested compounds is indicative of greater charge mobility in them. PTB7-Th donor was employed to calculate open circuit voltage of all investigated molecules. N1–N5 molecules had improved optoelectronic properties, significant probable power conversion efficiency as evident from their absorption aspects, high values of Voc, and fill factor, compared to R molecule. Designed A-D-A type NF based molecules make OSCs ideal for use in wearable devices, building-integrated photovoltaics and smart fabrics.

Directed Message Passing Neural Network for Predicting Power Conversion Efficiency in Organic Solar Cells.

Organic solar cells (OSCs) have emerged as a promising technology for renewable energy generation, and researchers are constantly exploring ways to improve their efficiency. For prediction of photovoltaic properties in OSCs, many machine learning models have been used in the past. All the models are used with fixed molecular descriptors and molecular fingerprints as input for power conversion efficiency (PCE) prediction. Recently, the graph neural network (GNN), which can model graph structures of the molecule, has received increasing attention as a method that could potentially overcome the limitations of fixed descriptors by learning the task-specific representations using graph convolutions. In this study, we have used the directed message passing neural network (D-MPNN), an emerging type of GNN for predicting PCE of organic solar cells, and the results are compared for the same train and test set with fixed descriptors and fingerprints. The excellent performance demonstrated by the D-MPNN model in this investigation highlights its potential for predicting PCE, surpassing the limitations of conventional fixed descriptors.

The impact of structural modifications into benzodithiophene compounds on electronic and optical properties for organic solar cells

To meet the energy demands, fullerene-free organic systems have been emerging as efficient photovoltaic materials. Therefore, we have tailored benzodithiophene-based A-π-D-π-A configured, MBT1-MBT9 derivatives after end-capped modifications in MBTR. A comparative study between theoretical λmax values of MBTR at different levels of density functional theory (DFT) and experimental was executed in order to select appropriate functional for current study. Owing to the close harmony between the results of M06/6-311G(d,p) level and experimental findings, the aforesaid function/basis set was selected for the further investigation. Different analyses such as binding energy (Eb), transition density matrix (TDM), global reactivity parameters (GRP), open-circuit voltage (Voc), optical properties (UV–Vis), hole electron and frontier molecular orbital (FMO) energies, were computed to probe the photovoltaic properties of MBTR and MBT1-MBT9. The addition of different acceptors in MBT1-MBT9, lessen the energy gap (ΔE = 2.362–2.000 eV) along with the increase in bathochromic shift (λmax = 651.657–766.672 nm) compared to the reference chromophore (ΔE = 2.672 eV and λmax = 585.466 nm). In addition, FMO findings revealed the significant charge transference from HOMO towards LUMO, which were further supported by TDM maps. Interestingly, all the tailored molecules exhibit low Eb (0.459–0.383 eV), which indicates the higher exciton dissociation in MBT1-MBT9. Comparable results of Voc for MBT1-MBT9 and MBTR were obtained via HOMOPBDBT−LUMO Acceptor. Among all the derivatives, due to least band gap, wider absorption spectrum and lower Eb along with higher exciton dissociation rate in MBT9, excellent photovoltaic properties were examined in this derivative. All these analyses support conceptualized compounds as efficient photovoltaic materials and encourages the experimentalists to synthesize these compounds to obtain proficient photovoltaic materials.

Theoretical designing of symmetrical non-fullerene acceptor molecules by end-capped modification for promising photovoltaic properties of organic solar cells

Non-fullerene small molecules must absorb in a broader wavelength range for achieving high efficiencies. This work presents seven indacenodithiophene core-based acceptor molecules (SJA1-SJA7) designed by structurally tailoring the pre-existed SJ-IC molecule. Detailed studies of these newly designed molecules were carried out to analyze the stabilization of energy levels, planarity, UV–Visible absorption, light-harvesting efficiency, open circuit voltage (Voc), and other photovoltaic properties. Structural modification with different acceptors resulted in the narrowing of band gap and broader absorption spectrum. All the newly reported molecules showed significant redshift having λmax values ranging from 686 nm to 722 nm in the gas phase and 742 nm to 792 nm in chloroform as compared to SJ-IC which has λmax values at 675 nm and 732 nm in gas and chloroform medium respectively. Moreover, newly presented molecules exhibited lower excitation energy values and higher oscillator strength than SJ-IC molecule which indicate effective charge transfer between frontier molecular orbitals. Improved charge mobilities were observed as newly developed molecules possessed lower internal reorganization energies. These findings were further confirmed by molecular electrostatic potential (MEP) and transition density matrix (TDM) analysis. In case of Voc, SJA7 emerged as a more proficient molecule due to its higher value (1.440 eV) than SJ-IC (1.42 eV). These results assure the remarkable improvement in optoelectronic properties of designed molecules which makes them a better choice than pre-existing SJ-IC molecule for the development of improved OSCs in the future.

Modified optoelectronic parameters by end-group engineering of A-D-A type non-fullerene-based small symmetric acceptors constituting IBDT core for high-performance photovoltaics

End-chain exploration of Non-Fullerene Acceptors is an efficient approach to amplify the photovoltaic properties of organic solar cells (OSCs). This green energy technology has attained tremendous consideration from scientists in the last few decades. Current investigations on OSCs have presented remarkable optoelectronic applications of A-D-A-type (A = acceptor and D = donor unit) molecules comprising seven newly designed molecules (INIC1–INIC7) due to their reduced band gaps, red-shifting of optical profiles towards the visible region, Light Harvesting Efficiency (LHE), improved dipole moment, ionization potential (IP), and electron affinity (EA). These parameters are analyzed using the DFT (density functional theory) and TD-DFT (time-dependent-density functional theory) approaches with varying functionals. Numerous specifications like orbital analysis including frontier molecular and natural transition orbital (FMO and NTO) evaluation, as well as density of states (DOS), transition density matrix (TDM), molecular electrostatic potential (MEP) investigation, and various other parameters have demonstrated that the refinement in these factors is attributed to the presence of an IBDT core with seven distinct NFFRAs (Non-Fullerene Fused Ring Acceptors). Amongst the designed molecules, several have exhibited superior features to the modeled molecule. The charge carrier mobilities of different proposed molecules have yielded magnificent results compared to the reference molecule, which is ultimately scrutinized by TDM graphs. The Voc (open-circuit voltage) of INIC5 capitulates preferable impact, which could lead to substitution of all-other molecules in the field of OSCs. Consequently, the impressive dipole moment cooperates in establishing the non-covalent interactions with chloroform leading to exceptional maneuverability. Nonetheless, various derived molecules have exhibited astonishing results concerning different examined parameters.

Increasing Charge Carrier Mobility through Modifications of Terminal Groups of Y6: A Theoretical Study.

The applications of non-fullerene acceptor Y6 with a new type of A1-DA2D-A1 framework and its derivatives have increased the power conversion efficiency (PCE) of organic solar cells (OSCs) up to 19%. Researchers have made various modifications of the donor unit, central/terminal acceptor unit, and side alkyl chains of Y6 to study the influences on the photovoltaic properties of OSCs based on them. However, up to now, the effect of changes of terminal acceptor parts of Y6 on the photovoltaic properties is not very clear. In the present work, we have designed four new acceptors-Y6-NO2, Y6-IN, Y6-ERHD, and Y6-CAO-with different terminal groups, which possess diverse electron-withdrawing ability. Computed results show that with the enhanced electron-withdrawing ability of the terminal group, the fundamental gaps become lower; thus, the wavelengths of the main absorption peaks of UV-Vis spectra red-shifts and total oscillator strength increase. Simultaneously, the electron mobility of Y6-NO2, Y6-IN, and Y6-CAO is about six, four, and four times faster than that of Y6, respectively. Overall, Y6-NO2 could be a potential NFA because of its longer intramolecular charge-transfer distance, stronger dipole moment, higher averaged ESP, enhanced spectrum, and faster electron mobility. This work provides a guideline for the future research on modification of Y6.

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.

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.

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.

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

Terpolymers and additional π-bridges regulations for improving fill factors in efficient organic solar cells

For efficient organic solar cells (OSCs), the fill factor (FF) plays a significant role in power conversion efficiency (PCE), which are closely related to molecular stacking and active layer morphology. For polymer design, a feasible strategy to solve this problem is constructing irregular conjugated backbones, such as random terpolymers. In this work, difluorinated benzothiadiazole (SZ) units are introduced into PM7 to synthesize terpolymers. By the SZ units and paired π-bridges, the favorable molecular stacking and active layer morphology can be obtained, which contributes to FF and PCE improving from 61% and 13% of PM7-based OSCs to 71% and 15% of the terpolymer-based OSCs, respectively. Quantum chemistry optimizations reveal that additional π-bridges can adjust the localized planar conformation between the donor and acceptor units. The reduced density gradient function and the independent gradient model approach suggest that different additional π-bridges can promote their effective stacking of SZ units by balancing intra-molecular attraction and repulsion and enhancing intermolecular interactions. This work demonstrates the practicality of terpolymer design and paves a way to improve molecular stacking and morphological properties for efficient OSCs.