Power Conversion Efficiency Of Organic Solar Cells Research Articles

Systematic Engineering of Near-Infrared Small Molecules Based on 4H-Cyclopenta[1,2-b:5,4-b']dithiophene Acceptors for Organic Solar Cells.

Nonfullerene acceptors (NFAs) have emerged as tremendous materials, efficiently advancing bulk-heterojunction organic solar cells (OSCs) technology. Unlike their fullerene counterparts, NFAs offer the unique advantage of finely tunable electronic energy levels and optical characteristics, which correspond to substantial enhancement in power conversion efficiency of OSCs. Herein, we have introduced a new series of near-infrared NFAs (AY1-AY8) to advance this technology further. Our research deeply investigates the structure-property relationship and thoroughly explores the optical, optoelectronics, photophysical, and photovoltaic characteristics of a synthetic reference molecule (R) and the modeled AY1-AY8 NFAs series. We performed advanced quantum chemical simulations using density functional theory (DFT) and time-dependent DFT methods. Additionally, we also estimated key geometric characteristics such as frontier molecular orbitals, hole-electron overlap, density of states, molecular electrostatic potential, molecular excitation and binding energies, transition density matrix, and reorganizational energy of electrons and holes and compared them with those of a synthetic reference molecule (R). Our findings show that all designed materials (AY1-AY8) exhibit red-shift absorption, improved electronic charge mobility, and low binding and excitation energies compared to R. Notably, these designed materials (AY1-AY8) display significantly narrower electronic energy gaps (E g 1.89-1.71 eV), indicating enhanced charge shifting from the highest occupied molecular orbital to lowest unoccupied molecular orbital and broadening of the absorption spectrum. Moreover, we also revealed a comprehensive study of the donor/acceptor complex of PTB7-Th/AY8 to understand charge shifting between donor and acceptor molecules. Therefore, we strongly recommend this designed (AY1-AY8) series to the experimentalists for the future development of highly efficient OSC devices.

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.

Intrinsic Advantage of Fused‐Ring Nonfullerene Acceptor‐Based Organic Solar Cells to Reduce Voltage Loss

The large voltage loss is a significant disadvantage of organic solar cells (OSCs) compared with inorganic and perovskite solar cells and should be reduced to further improve the power conversion efficiency of OSCs. Herein, the voltage loss in OSCs with a systematically controlled energy difference between the excited and charge transfer states is discussed. The voltage loss is compared between two types of OSCs: narrow‐bandgap donors paired with wide‐bandgap acceptors and narrow‐bandgap fused‐ring nonfullerene acceptors (NFAs) paired with wide‐bandgap donors, to elucidate whether there are any essential advantages in the latter. The first advantage of narrow‐bandgap‐NFA‐based OSCs is their higher photoluminescence quantum yield, owing to their rigid fused‐ring architecture. The second advantage is the ability to achieve efficient charge separation with a small voltage loss.

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.

Designing of Un-Fused Electron Acceptors with Enhanced Power Conversion Efficiency by Introducing Unique S–O Noncovalent Interaction

Terminal units’ modification is an effective strategy for designing efficient un-fused nonfullerene acceptors (UF-NFAs) with enhanced power conversion efficiency (PCE). Nowadays, researchers are focused on designing new UF-NFAs that enhance the PCE of organic solar cells. In this line, efforts are being made to design new UF-NFAs for possible application on organic solar cells (OSCs). By doing terminal unit modification of the Cl-4F molecule, we have designed a new series of UF-NFA (ETPJ-1–ETPJ-4). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the B3LYP/6-311G([Formula: see text]) level have been employed for the computation of various geometric and photovoltaic aspects. Energies of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) with their band gap suggested that ETPJ-1–ETPJ-4 are effective contributors to the design of the efficient active layer of OSCs. Red-shift (near IR) in the absorption spectrum with easy excitation of exciton has been noted in ETPJ-1–ETPJ-4. Enhanced open circuit voltage with high fill factor percentage (FF%) was also noted for designed systems. Further, the PCE values of the ETPJ-1–ETPJ-4 are better than the reference molecule. So, we recommended a novel kind of unfused nonfullerene acceptors (NFAs) with unique S–O noncovalent interaction for possible application in OSCs.

Charge generation in organic solar cells: Journey toward 20% power conversion efficiency

AbstractThe power conversion efficiencies of organic solar cells (OSCs) have routinely lagged far behind those of their inorganic counterparts. However, owing to the enormous contributions of many researchers, the power conversion efficiencies of OSCs have rapidly improved and now exceed 19%. The charge generation mechanisms in OSCs have been heavily debated during this period while acquiring valuable knowledge. This review highlights fundamental and cutting‐edge research that rationalizes why OSCs can generate photocurrent so efficiently. In particular, a photophysicist's views on exciton diffusion to donor:acceptor interfaces, charge transfer at the donor:acceptor interface, and long‐range spatial dissociation of charge transfer states are discussed. Although a general consensus in this area has not been reached yet, recent time‐resolved spectroscopic measurements provide important photophysical insights that can help achieving a better understanding of the charge generation mechanism in OSCs. Based on these observations, future research directions for realizing further improvements in OSC performance are discussed.

KESAN KETEBALAN LAPISAN PENGANGKUT ELEKTRON TIO2 TERHADAP PRESTASI SEL SURIA ORGANIK: KAJIAN SIMULASI

Organic solar cell has gained more attention due to its low-cost production and easy fabrication process. However, the power conversion efficiency (PCE) is still low as compared to that of inorganic solar cell. One of the approaches to improve the PCE of organic solar cell is by introducing an electron transport layer which can extract the electrons effectively in between photoactive layer and cathode. Simulation study using SCAPS (Solar Cell Capacitance Simulator) software was conducted to examine the effects of TiO2 electron transport layer thickness on the performance of organic solar cell with ITO/TiO2/P3HT:PCBM/Ag structure. P3HT:PCBM acted as photoactive layer, whereas ITO and Ag played roles as cathode and anode, respectively. The range of studied thickness was from 30 to 180 nm. The simulation result indicates that the PCE increased with TiO2 layer thickness in the range of 30 to 120 nm, and it saturated when the TiO2 layer thickness was further raised to 180 nm. The highest PCE of 2.139% was obtained at TiO2 layer thickness of 180 nm.

Understanding interfacial energy structures in organic solar cells using photoelectron spectroscopy: A review

Organic solar cells (OSCs) have received considerable attention as a promising clean energy-generating technology because of their low cost and great potential for large-scale commercial manufacturing. With significant advances in new charge-transport material design, interfacial engineering, and their operating conditions, power conversion efficiencies of OSCs have continued to increase. However, a fundamental understanding of charge carrier transport and especially how ionic moieties affect carrier transport is still lacking in OSCs. In this regard, photoelectron spectroscopy has provided valuable information about interfacial electronic structures. The interfacial electronic structure of OSC interlayers greatly impacts charge extraction and recombination, controls energy level alignment, guides active layer morphology, improves material’s compatibility, and plays a critical role in the resulting power conversion efficiency of OSCs. Interfacial engineering incorporating inorganic, organic, and hybrid materials can effectively enhance the performance of organic photovoltaic devices by reducing energy barriers for charge transport and injection while improving compatibility between metal oxides and donor–acceptor based active layers or transparent conducting electrodes. This article provides a review of recent developments in interfacial engineering underlying organic photovoltaic devices of donor–acceptor interfaces.

Morphological Stabilization in Organic Solar Cells via a Fluorene-Based Crosslinker for Enhanced Efficiency and Thermal Stability.

Power conversion efficiencies (PCEs) and device stability are two key technical factors restricting the commercialization of organic solar cells (OSCs). In the past decades, though the PCEs of OSCs have been significantly enhanced, device instability, especially in the state-of-the-art nonfullerene system, still needs to be solved. In this work, an effective crosslinker (namely, DTODF-4F), with conjugated fluorene-based backbone and crosslinkable epoxy side-chains, has been designed and synthesized, which is introduced to enhance the morphological stabilization of the PM6:Y6-based film. This crosslinker with two epoxy groups can be in situ crosslinked into a stable network structure under ultraviolet radiation. We demonstrate that DTODF-4F, which acted as a third component, can promote the exciton dissociation rate and reduce traps/defects, finally resulting in the enhancement of efficiency. In particular, the OSC devices exhibit better stability under continuous heating owing to the morphology fixation of the bulk heterojunction. This work drives the development direction of morphological stabilization to further improve the performance and stability of OSCs.

In silico modelling of acceptor materials by End-capped and π-linker modifications for High-Performance organic solar Cells: Estimated PCE > 18%

Efficient acceptor materials are of great importance in improving the performance of organic solar cells. Electron transport materials play a crucial role in improving the power conversion efficiency (PCE) of photovoltaic devices. In recent years, great efforts have been made to develop new acceptor materials that can be used in organic solar cells (OSCs). Previous reports have shown the high efficiency of CH1007 as an acceptor material in OSCs application. In this study, we used CH1007 as a reference molecule (R) and developed four new acceptor materials (CF1-CF4) derived from CH1007 based on the tuning of the end-capped and π-linker units within the conjugated framework. Density functional theory calculations (DFT) were performed to determine the structural, optoelectronic, and charge transfer properties of the developed materials. CF1-CF4 exhibited narrow band gaps with a redshift of the absorption maxima compared to R, which will lead to an improvement in the PCE of OSC. Low reorganization energies of holes and electrons were determined for the designed molecules compared to the reference molecule, indicating high charge carrier transport within these molecules. Transition density matrix (TDM) analysis revealed the movement of electron density from the core block to the acceptor moieties via π-linkages. The photovoltaic parameters were investigated and we found a relevant open-circuit voltage (Voc) for the designed molecules. A mixing study was performed for PTB7-Th: CF3, which gave interesting results. Based on the founding results and comparison with R, we found that the designed molecules are promising materials that can be used as acceptors for high-efficiency OSCs.

Strongly Reduced Non-Radiative Voltage Losses in Organic Solar Cells Prepared with Sequential Film Deposition.

With nearly 100% yields for mobile charge carriers in organic solar cells (OSCs), the relatively large photovoltage loss (ΔVoc) is a critical barrier limiting the power conversion efficiency of OSCs. Herein, we aim to improve the open-circuit voltage (Voc) in OSCs with non-fullerene acceptors via sequential film deposition (SD). We show that ΔVoc in planar heterojunction (PHJ) devices prepared by the SD method can be appreciably mitigated, leading increases in Voc to 80 mV with regard to the Voc of bulk heterojunction devices. In PHJ OSCs, the energy level of intermolecular charge-transfer states is found to increase with a decrease in the level of aggregation in the solid state. These properties explain the enhanced electroluminescent quantum efficiency and resultant suppression of the voltage losses induced by nonradiative charge recombination and interfacial charge transfer. This work provides a promising strategy for tackling the heavily discussed photovoltage loss in OSCs.

10.18% PCE of organic solar cells with pyramid micron-structured PDMS

Since the light harvesting of the organic solar cells (OSCs) is limited by the ultra-thin active layer film due to the low carrier mobility of the organic materials. This study presents a tractable and cost-effective method for enhancement of the light capture of OSCs. A pyramid-shaped micron-structured polydimethylsiloxane (MST-PDMS) anti-reflection film was pasted on the back surface of the OSCs. The MST-PDMS film can reduce the reflectivity of incident light and enhance light capture. Comparing with that of the devices based on the normal indium tin oxide (ITO) glass substrates, the performance of the devices with MST-PDMS was significant improved. The size of the pyramid is an important factor to the performances of the devices. The short circuit current density could increase mostly without sacrificing the open circuit voltage and fill factor, when the width of the pyramid is 9 µm, and a maximum power conversion efficiency (PCE) of PTB7-Th: PC71BM-based OSCs reaches to 10.18%. Compared with that of the device without the anti-reflection film, PCE was increased by 17.96%. Further, the OSCs with the pyramid-shaped MST-PDMS exhibits a relatively high hydrophobic properties leading to a better stability of the devices at the ambient environment.

Self-cleaning organic solar cells based on micro/nanostructured haze films with optical enhancement effect

We present a self-cleaning organic solar cells (OSCs) with a light-trapping structure by introducing a groove-shaped micro/nanostructured haze thin films (GHFs). The GHF with periods larger than wavelengths of incident light can broaden the effective optical paths and promote the diffused lights, while keeping high (low) total transmission (reflectance) properties. When laminated GHF on top of the light-in side of OSCs, the power conversion efficiency of OSCs is improved more than 10%. Simultaneously, the superhydrophobic GHF composed of the groove structure allows the droplets to successfully remove dust particles from the polydimethylsiloxane (PDMS) surface during the roll-off process of the drop. Under 10 cycles of dust contamination and cleaning treatment, OSCs with GHF can still guarantee an initial efficiency of 84% (76%), showing great potentials of OSCs in practical applications.

Tuning Optoelectronic Properties of Dithienopyrrole Donor Molecules for Organic Solar Cells

Theoretical analysis of physical properties of organic solar cells (OSCs) are important in order to reveal the correlation between power conversion efficiencies (PCE), structure and properties. Five new A‒D‒A type small molecules M1, M2, M3, M4, and M5 were designed by using dithienopyrrole (DTP) as electron rich donor unit with different types of π-spacers and end capped acceptor units. Functional MPW1PW91/6-31G(d,p) level of theory was used to optimize the geometry of all molecules. For excited state calculation TD-MPW1PW91/6-31G(d,p) level of theory was used. The geometries, electronic structures, dipole moment, open circuit voltage, reorganization energies and charge transport properties of designed molecules (M1 $$ - $$ M5) have been scrutinized comparing with the reported compound R. The results revealed that the HOMO energy levels of molecules M1, M2, M3, and M5 were lower while M4 was of high energy level thus facilitate the donation of electron as compared to references molecule R. While LUMO energy level of all the molecules were slightly high energy due electron withdrawing effects of spacer and acceptor moiety. Highest energy gap of HOMO–LUMO was observed in M1 which was 2.48 eV and M3 showed low energy gap (2.11 eV) as compared to other designed molecules. All molecules showed low values for λe, so they have high rate of electron transfer as compared to R. All designed molecules exhibited higher value of dipole moment as compared to reference molecule R except M1. Higher value of dipole moment of donor molecules contrary to reference means good solubility towards organic solvents which is beneficial for further solar cell device fabrication. All designed molecules show higher Voc values except M4 which has comparable Voc with respect to reference molecule R. In short, choice of appropriate electron withdrawing and donating groups is very important for improving power conversion efficiencies of OSCs.

Pyrene-Imidazole Based Aggregation Modifier Leads to Enhancement in Efficiency and Environmental Stability for Ternary Organic Solar Cells.

A novel pyrene-imidazole derivative (PyPI), which can form effcient π-π stacking in solid film, has been utilized in organic solar cells (OSCs). The stacking of small a molecule PyPI can facilitate a charge transfer and suppress fullerene aggregation. As a result, PTB7-Th: PyPI: PC71BM based ternary OSC exhibits a high power conversion efficiency (PCE) of 10.36%, which presents a 15.88% increase from the binary device (8.94%). Concurrently, the ternary OSC shows a much better thermal and light illumination stability. Under continuous 60°C annealing for 3 h, in atmosphere, the device still remains at 94.13% efficiency more than the pristine state, while the control device remains at 52.47% PCE. Constant illumination under Air Mass (AM) 1.5G irradiation (100 mW cm−2) in atmosphere, the PCE of OSC remains at 72.50%. The high conversion efficiency and excellent environmental stability of the PyPI based ternary OSC, has narrowed the gap between laboratory investigation and industrial production.

Enhanced efficiency of ternary organic solar cells by doping a polymer material in P3HT:PC61BM

Doping a low‐bandgap polymer material (PDTBDT‐DTNT) as a complementary electron donor in poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61‐butyricacid methyl ester (PC61BM) blend is experimented to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The PCE of OSCs was increased from 3.19% to 3.75% by doping 10 wt% PDTBDT‐DTNT, which was 17.55% higher than that of the OSCs based on binary blend of P3HT:PC61BM (host cells). The short‐circuit current density (Jsc) was increased to 10.11 mA·cm−2 compared with the host cells. Although the PCE improvement could partly be attributed to more photon harvest for complementary absorption of 2 donors by doping appropriate PDTBDT‐DTNT, the promotion of charge separation and transport as well as the suppression of charge recombination due to a matrix of cascade energy levels is also important. And the better morphology of the active layer films is beneficial to the optimized performance of ternary devices.

The Effect of Donor and Nonfullerene Acceptor Inhomogeneous Distribution within the Photoactive Layer on the Performance of Polymer Solar Cells with Different Device Structures.

Due to the inhomogeneous distribution of donor and acceptor materials within the photoactive layer of bulk heterojunction organic solar cells (OSCs), proper selection of a conventional or an inverted device structure is crucial for effective exciton dissociation and charge transportation. Herein, we investigate the donor and acceptor distribution within the non-fullerene photoactive layer based on PBDTTT-ET:IEICO by time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) and scanning Kelvin probe microscopy (SKPM), indicating that more IEICO enriches on the surface of the photoactive layer while PBDTTT-ET distributes homogeneously within the photoactive layer. To further understand the effect of the inhomogeneous component distribution on the photovoltaic performance, both conventional and inverted OSCs were fabricated. As a result, the conventional device shows a power conversion efficiency (PCE) of 8.83% which is 41% higher than that of inverted one (6.26%). Eventually, we employed nickel oxide (NiOx) instead of PEDOT:PSS as anode buffer layer to further enhance the stability and PCE of OSCs with conventional structure, and a promising PCE of 9.12% is achieved.

Cooptimization of Adhesion and Power Conversion Efficiency of Organic Solar Cells by Controlling Surface Energy of Buffer Layers

Here, we demonstrate the cooptimization of the interfacial fracture energy and power conversion efficiency (PCE) of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT)-based organic solar cells (OSCs) by surface treatments of the buffer layer. The investigated surface treatments of the buffer layer simultaneously changed the crack path and interfacial fracture energy of OSCs under mechanical stress and the work function of the buffer layer. To investigate the effects of surface treatments, the work of adhesion values were calculated and matched with the experimental results based on the Owens-Wendt model. Subsequently, we fabricated OSCs on surface-treated buffer layers. In particular, ZnO layers treated with poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) simultaneously satisfied the high mechanical reliability and PCE of OSCs by achieving high work of adhesion and optimized work function.

Plasmonic Effect of Gold Nanostars in Highly Efficient Organic and Perovskite Solar Cells.

Herein, a novel strategy is presented for enhancing light absorption by incorporating gold nanostars (Au NSs) into both the active layer of organic solar cells (OSCs) and the rear-contact hole transport layer of perovskite solar cells (PSCs). We demonstrate that the power conversion efficiencies of OSCs and PSCs with embedded Au NSs are improved by 6 and 14%, respectively. We find that pegylated Au NSs are greatly dispersable in a chlorobenzene solvent, which enabled complete blending of Au NSs with the active layer. The plasmonic contributions and accelerated charge transfer are believed to improve the short-circuit current density and the fill factor. This study demonstrates the roles of plasmonic nanoparticles in the improved optical absorption, where the improvement in OSCs was attributed to surface plasmon resonance (SPR) and in PSCs was attributed to both SPR and the backscattering effect. Additionally, devices including Au NSs exhibited a better charge separation/transfer, reduced charge recombination rate, and efficient charge transport. This work provides a comprehensive understanding of the roles of plasmonic Au NS particles in OSCs and PSCs, including an insightful approach for the further development of high-performance optoelectronic devices.

Recent Advances in Wide-Bandgap Photovoltaic Polymers.

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials.