Application In Organic Solar Cells Research Articles

Theoretical study of dipyridine phenanthrene derivatives for BHJ organic solar cells application: a DFT approach

Theoretical study of dipyridine phenanthrene derivatives for BHJ organic solar cells application: a DFT approach

Deciphering the role of invited guest bridges in non-fullerene acceptor materials for high performance organic solar cells

Fullerene-free acceptor molecules gained great attention of researchers due to their excellent light harvesting capability and low toxicity rate. Herein, six new molecules have been designed by bridging core modifications and analyzed through advanced quantum chemical techniques. Density functional theory and time dependent-DFT have been employed in order to compute optoelectronic, photovoltaic and physiochemical properties of newly designed molecules. Some geometric parameters like alignment of both molecular orbitals, absorption maxima, excitation with binding energies, open circuit voltage, and transition density matrix have been performed in order to examine the structural-property relationship of designed molecules. Efficient bridge atoms of designed molecules cause reduction in energy band gap (1.895–2.375 eV) along with red-shifting in absorption maxima (619–719 nm). Transition density matrix analysis unveils the location of charge density within a molecule along with different transitions. Molecular electrostatic potential analysis suggested that the theoretical planned molecules are symmetrical and have electron rich and poor regions. High open circuit voltage and electron-hole mobility advocated that the designed molecules are good nominees for high performance organic solar cell applications.

Explore fused-ring core incorporated A-π-D-π-A type acceptors and their application in organic solar cells: Insight into molecular conformation, optical and electrochemical properties, film morphology, and energy loss

Acceptor-π-Donor-π-Acceptor (A-π-D-π-A) type fused-ring electron acceptors (FREAs) are a class of important nonfullerene acceptors for fabricating high efficiency organic solar cells (OSCs). However, limited by the rare types of the central D core, the efficiencies of the OSCs based on A-π-D-π-A FREAs are falling behind. In this work, dithienopyrrolobenzothiadiazole (DTPBT) was employed in developing A-π-D-π-A type FREAs, and was assessed as a D core. DTPBT based FREAs were synthesized and compared with the typical A-π-D-π-A type FREAs using IDT as the D core, from aspects of molecular conformation, optical and electrochemical properties, blend film morphology, and energy loss. Compared to traditional IDT based A-π-D-π-A type FREAs (IRIC-4F), A-π-D-π-A FREAs containing DTPBT (BTOT-OD-4F) showed C-type molecular conformation, redshifted absorption and downshifted energy levels. As a result, the corresponding devices achieved an efficiency of over 13% with improved JSC of 23.44 mA cm−2 and a fair FF of 66.9%. Meanwhile, the energy loss of the PBDB-T: BTOT-OD-4F blends reduced effectively, due to the contribution of suppressed nonradiative recombination. Above all, DTPBT has presented its potential in developing highly efficient A-π-D-π-A type FREAs. To realize the best performance of the novel acceptors, further systematic and synergetic optimization of the molecule structure and device fabrication are needed. This work has demonstrated a new design manner of A-π-D-π-A type FREAs through exploring novel fused-ring cores, which facilitates reduced energy loss of the corresponding devices.

Semitransparent organic solar cells based on all-low-bandgap donor and acceptor materials and their performance potential

Recent advances in organic solar cells (OSCs) based on large-bandgap donors and low-bandgap non-fullerene acceptors (NFAs) have increased the power conversion efficiency (PCE) of OSCs to ~18%. However, these state-of-the-art OSCs have strong absorption in the visible region, limiting their application in semitransparent organic solar cells (STOSCs). In this study, an all-low-bandgap system based on a low-bandgap polymer donor (PM2) and a low-bandgap NFA (Y6-BO), was introduced as the light-harvesting layer for STOCSs with absorption mainly localized in the near-infrared (NIR) spectrum from 600 to 900 nm. The corresponding opaque OSCs exhibited the highest PCE among reported all-low-bandgap OSC systems, and the corresponding STOSCs showed higher visible light transmittances (VLTs) and light utilization efficiencies (LUEs) than the reference devices based on state-of-the-art PM6:Y6-BO OSC system with broad range absorption from visible to NIR. Optical simulations predicted that the PM2:Y6-BO-based STOSCs have a greater potential to realize higher VLTs and PCEs and better PCE retention (PCEsemitransparent/PCEopaque) than those from the PM6:Y6-BO-based STOSCs. Guided by these simulations, PM2-based STOSCs with VLTs exceeding 40% and PCEs of ~6% were achieved. Further recombination analysis suggested that the PM2-based devices experienced more severe charge recombination and energy losses, indicating there is further room for PCE improvement by designing new all-low-bandgap systems. Overall, this work shows the great potential of all-low-bandgap systems in realizing STOSCs with high PCEs and VLTs, which is promising for the commercialization of OSCs as power-generating window applications.

Recent Advances of Chlorination in Organic Solar Cells

AbstractChlorination has been used in the fields of organic solar cells (OSCs) for a long time, and impressive progress has been made over the years. Recently developed chlorinated OSCs have achieved an efficiency of over 18%. For better understanding and application of chlorination in the fields of OSCs, we will briefly introduce the general properties of chlorine and recent advances in its introduction and applications in OSCs in this cluster article. Finally, we also provide a short discussion of current questions regarding chlorination in OSCs and future developments in this area.

Utilizing 3,4-ethylenedioxythiophene (EDOT)-bridged non-fullerene acceptors for efficient organic solar cells

A rational design of efficient low-band-gap non-fullerene acceptors (NFAs) for high-performance organic solar cells (OSCs) remains challenging; the main constraint being the decrease in the energy level of the lowest unoccupied molecular orbitals (LUMOs) as the bandgap of A-D-A-type NFAs decrease. Therefore, the short current density (Jsc) and open-circuit voltage (Voc) result in a trade-off relationship, making it difficult to obtain efficient OSCs. Herein, three NFAs (IFL-ED-4F, IDT-ED-4F, and IDTT-ED-2F) were synthesized to address the above-mentioned issue by introducing 3,4-ethylenedioxythiophene (EDOT) as a π-bridge. These NFAs exhibit relatively low bandgaps (1.67, 1.42, and 1.49 eV, respectively) and upshifted LUMO levels (-3.88, −3.84, and −3.81 eV, respectively) compared with most reported low-band-gap NFAs. Consequently, the photovoltaic devices based on IDT-ED-4F blended with a PBDB-T donor polymer showed the best power conversion efficiency (PCE) of 10.4% with a high Jsc of 22.1 mA cm−2 and Voc of 0.884 V among the examined NFAs. In contrast, IDTT-ED-4F, which was designed with an asymmetric structure of the D-π-A type, showed the lowest efficiency of 1.5% owing to the poor morphology and charge transport properties of the binary blend. However, when this was introduced as the third component of the PM6:BTP-BO-4Cl, complementary absorption and cascade energy-level alignment between the two substances could be achieved. Surprisingly, the IDTT-ED-4F-based ternary blend device not only improved the Jsc and Voc, but also achieved a PCE of 15.2%, which is approximately 5.3% higher than that of the reference device with a minimized energy loss of 0.488 eV. In addition, the universality of IDTT-ED-2F as a third component was effectively demonstrated in other photoactive systems, specifically, PM6:BTP-eC9 and PTB7-Th:IEICO-4F. This work facilitates a better understanding of the structure–property relationship for utilizing efficient EDOT-bridged NFAs in high-performance OSC applications.

Charge transfer evidence in donor–acceptor single‐walled carbon nanotubes filled with sexithiophene oligomers: Nanotube diameter dependence

AbstractEncapsulation of photoactive organic molecules inside single‐walled carbon nanotubes (SWNTs) appears to be of great interest in terms of high power conversion efficiency and long‐term stability for a commercial application of organic solar cells (OSCs). In this paper, we report a charge transfer (CT) evidence in donor–acceptor SWNTs filled with Sexithiophene oligomers (6T) by Raman spectroscopy. To compute the optimal diameter and demonstrate the most stable structure of the hybrid systems with either a single 6T molecule encapsulated into SWNTs (6T@SWNTs), or two 6T chains encapsulated (6T‐6T@SWNTs), we have performed structural geometry optimization on the hybrid encapsulated systems using a convenient Lennard–Jones (LJ) expression of the van der Waals (vdW) intermolecular potential. Combining the density functional theory (DFT), molecular mechanics, bond polarizability model, and the spectral moment method (SMM), we computed the polarized nonresonant Raman spectra of 6T molecule and SWNTs (metallic and semiconducting) before and after encapsulation. The influence of the encapsulation on the Raman‐active modes of the 6T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. In particular, significant changes observed in the G‐band wavenumber. The possibility (or not) of an eventual CT between the 6T oligomer and the nanotube in both hybrid systems (6T@SWNTs and 6T‐6T@SWNTs) is discussed. We show that there is a dependence of the CT with respect to the diameter of SWNTs, the CT vanish with increasing diameter of the nanotubes. Our finding of CT behavior in the filled SWNTs with respect to SWNT diameter will provide a useful guidance for enhancing the performance of OSCs by SWNTs.

Molecular engineering of narrow bandgap porphyrin derivatives for highly efficient photothermal conversion

Organic dyes based on porphyrin derivatives have been widely reported to show promising application in dye-sensitized solar cells and organic solar cells due to their desired power conversion efficiency and extinction coefficient while their photothermal conversion performance is rarely reported, to date. Considering the design guideline of photothermal materials with wide near-infrared region absorption and large extinction coefficient, we designed and prepared a narrow bandgap donor-acceptor small molecule P(DPP)4 based on porphyrin and diketopyrrolopyrrole, which showed a photothermal efficiency of 73.2% under irradiation of 808 nm laser, due to its aggregation-induced radical and distinct nonradiative decay. Furthermore, in an interfacial-heating water evaporation system, P(DPP)4 exhibited an evaporation rate of 1.304 kg m−2 h−1 under 1 sun irradiation with a solar-energy-to-vapor efficiency of 90.6%, higher than most of the pure organic photothermal materials. This work provides a promising way for organic small molecules as solar absorbers with high solar-thermal conversion efficiency and reveals the great potential of organic semiconductors with aggregation-induced radical in photothermal materials.

Double-Cable Conjugated Polymers with Pendant Rylene Diimides for Single-Component Organic Solar Cells.

ConspectusConjugated polymers for application in organic solar cells (OSCs) have been developed from poly(phenylenevinylene) to poly(3-hexylthiophene) and then to "donor-acceptor" structures, providing power conversion efficiencies (PCEs) over 18% when blending with the electron acceptor as a two-component photoactive layer. Besides, graft-structural double-cable conjugated polymers that use an electron donor as conjugated backbones and an electron acceptor as pendant side units are one kind of conjugated polymer, in which charge carriers are generated in a single polymer. Therefore, double-cable conjugated polymers can be used as a single photoactive layer in single-component OSCs (SCOSCs). The covalently linked electron donor and acceptor enable double-cable polymers to maintain stable microstructures during long-term operation compared to two-component systems, which is very important for OSCs toward large-area applications. However, SCOSCs based on double-cable conjugated polymers provided PCEs below 3% in a long period, which is lagging far behind PCEs of two-component OSCs. The key reason for this is the limited number of chemical structures and the difficulty to tune the morphology in these polymers.In this Account, we provide an overview about our efforts on developing new double-cable conjugated polymers with rylene diimides as side units, and how to realize high PCEs in SCOSC devices. The studies start from developing a "functionalization-polymerization" method to synthesize the polymers containing rylene diimide acceptors, so that large amounts of double-cable conjugated polymers with distinct physical and electrochemical properties were obtained. Then, we will discuss how to control the nanophase separation in the crystalline region and optimize the miscibility in the amorphous region of double-cable polymers, simultaneously facilitating exciton dissociation and charge transport. With these efforts, a high PCE of 8.4% has been obtained, representing the record PCE in SCOSCs. In addition, the physical process and the stability of SCOSCs will be discussed. We hope that this account will inspire many innovative studies in this field and push the PCEs of SCOSCs to a new stage.

Toward Real Setting Applications of Organic and Perovskite Solar Cells: A Comparative Review

The development of efficient, reliable, and clean energy sources is one of the global priorities for enabling a sustainable transition toward a green society and economy. The third‐generation solar cells, such as organic solar cells (OSCs) and perovskite solar cells (PSCs), are among the most promising platforms for the generation of electrical power from sunlight for a wide range of applications. However, the widespread diffusion of emerging photovoltaics technologies is hampered by issues occurring in the translation of laboratory‐scale R&D efforts to real settings. Herein, starting from a thorough survey of latest research on OSC and PSC technologies, critical factors related to fabrication and operation of solar cells, especially in terms of materials properties/requirements and beyond metrics built on efficiency only, are analyzed. On this basis, OSCs and PSCs are compared in terms of their potential in real application scenarios, also highlighting their peculiarities in view of their future large‐scale utilization.

Heteroleptic Ruthenium(II) Complexes with 2,2'-Bipyridines Having Carbonitriles as Anchoring Groups for ZnO Surfaces: Syntheses, Physicochemical Properties, and Applications in Organic Solar Cells.

Heteroleptic ruthenium (II) complexes were used for sensitizing ZnO surfaces in organic solar cells (OSCs) as mediators with photoactive layers. The complexes [Ru(4,4'-X2-bpy)(Mebpy-CN)2]2+ (with X = -CH3, -OCH3 and -N(CH3)2; bpy = 2,2'-bipyridine; Mebpy-CN = 4-methyl-2,2'-bipyridine-4'-carbonitrile) were synthesized and studied by analytical and spectroscopical techniques. Spectroscopic, photophysical, and electrochemical properties were tuned by changing the electron-donating ability of the -X substituents at the 4,4'-positions of the bpy ring and rationalized by quantum mechanical calculations. These complexes were attached through nitrile groups to ZnO as interfacial layer in an OSC device with a PBDB-T:ITIC photoactive layer. This modified inorganic electron transport layer generates enhancement in photoconversion of the solar cells, reaching up to a 23% increase with respect to the unsensitized OSCs. The introduction of these dyes suppresses some degradative reactions of the nonfullerene acceptor due to the photocatalytic activity of zinc oxide, which was maintained stable for about 11 months. Improving OSC efficiencies and stabilities can thus be achieved by a judicious combination of new inorganic and organic materials.

End-capped engineering of bipolar diketopyrrolopyrrole based small electron acceptor molecules for high performance organic solar cells

Non-fullerene small acceptor molecules demonstrate promising photovoltaic properties supported the progress of organic solar cells (OSCs). In organic photovoltaics, non-fullerene small acceptor compounds are valuable than traditional fullerene-based acceptor molecules for their good contribution in organic solar cells. This research generally focusses on Bipolar Diketopyrrolopyrrole (F(DPP)2B2) based small electron acceptor compounds used for organic solar cells (OSCs). For this purpose, four newly developed A-D-A (Acceptor-Donor –Acceptor) type electron accepting compounds named as V1, V2, V3, and V4 are planned for organic solar cells to study their optoelectronic characteristics. MPW1PW91/6-31G(d,p) basis set was used for calculations of various geometric parameters. Among all these, newly designed molecules V1 is proven an appropriate compound for OSCs applications due to the photovoltaic characteristics like low band gap between HOMO and LUMO (1. 88 eV) and V3 molecule shows broader absorption λmax in the gas phase (741.62 nm) and chloroform solvent (785.95 nm). Molecule V2 exhibits the lowest value of mobility of electrons (0.0806 Eh). All the designed compounds exhibit better open-circuit voltage, fewer energies of excitations, the highest value of absorption, greater dipole moment, equivalent binding energies, well-organized transport of electron and hole as compared to reference R. Thus, these molecules are suggested to researchers for the future development of highly efficient OSCs.

Designing of U‐shaped acceptor molecules for indoor and outdoor organic solar cell applications

AbstractEfficient molecular modeling approaches draw great attention from the scientific community to further boost the photovoltaic performances of the solar cell's materials. For this purpose, various end‐capped and bridged‐core modifications have been carried out to construct a suitable molecule best fitted for solar cell applications. Herein, we have designed a small‐molecule‐based fullerene‐free acceptor materials (IOD1–IOD7) for organic solar cells (OSCs) by doing end‐capped modifications and characterized them theoretically by employing various quantum chemical density functional theory (DFT) and time‐dependent (DFT) approaches. Designed molecules IOD1–IOD7 disclosed narrow band gap (Eg = 2.104 to 2.194 eV) as compared to reference molecule (2.197 eV). Further, red shifting in absorption spectrum of designed molecules (λmax = 751 to 771 nm) is noted as compared to reference molecule (λmax = 749 nm), which suggested that designed molecules are efficient near infrared light absorber. Low reorganizational energy of electron in designed molecules (λe = 0.0159 to 0.0189 Eh) offers high charge mobility as compared to reference molecule. Low excitation energies (Ex = 2.10 to 2.43 eV) and low binding energies (Eb = 0.034 to 0.084 eV) are noted in designed molecules as compared to reference molecule (Ex = 2.56 eV and Eb = 0.087 eV) which demonstrated that designed molecules are better candidates for high‐performance organic solar cells. Open‐circuit voltages (Voc) values, electronic structures, frontier molecular orbitals, and charge transfer phenomenon have also been studied theoretically. The outcomes of these theoretical characterizations revealed that all the newly designed non‐fullerene acceptor materials exhibit a wide‐ranging absorption efficiency and exciton dissociation constant values, with quite lower LUMO energy level, ensuring a boost in various photo‐physical and in optoelectronic properties of the designed materials, which will eventually improve the power conversion efficiency (PCE) of the OSCs devices.

Flexible organic solar cells for biomedical devices

Organic solar cells (OSCs), particularly made based on solution processing methods, have made significant progress over the past decades through the concurrent evolution of organic photovoltaic materials and device engineering. Recently, high power conversion efficiencies around 18% and over 16% have been demonstrated in both rigid and flexible OSCs, respectively. While most of the OSC research has centered on efficiency and cost, their emerging and potential usages in many critical applications, particularly in biomedical fields have been rising. In this mini-review, we will briefly discuss the high-performance organic photovoltaic materials and the representative flexible OSCs to give a scope on the recent rapid development of OSCs. Besides, we will review some progress on the applications of OSCs in biomedical devices and integrated systems. The potential challenges associated with integrating OSCs for biomedical devices will be put forward.

Quantum chemical design of near‐infrared sensitive fused ring electron acceptors containing selenophene as π‐bridge for high‐performance organic solar cells

AbstractEnd‐capped acceptors modification of fused ring electron acceptors (FREAs) is an attractive strategy to boost the optoelectronic and photovoltaic properties of the materials. FREAs are also proven beneficial due to their tremendous applications in organic solar cells (OSCs). Among fused‐ring electronic species, small fullerene‐free FREAs have already been drawn more attention due to their near‐infrared sensitivity and constantly increasing efficiencies. Therefore, we have designed six new FREAs (K1–K6) having selenophene as π‐bridge in between the central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after the incorporations of various end‐capped acceptors on to the recently synthesized IDT2SeC2C4‐4F molecule. Structural–property relationship and photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Certain critical specifications like frontier molecular orbitals (FMOs) alignment, density of states (DOS), absorption maxima, excitation energy, binding energy (BE) along with transition density matrix (TDM), and the specifically estimated reorganizational energy values of electron and hole and the open circuit voltages of newly designed molecules are computed and compared with reference molecule. Generally, a red‐shifting absorption behavior of FREAs is considered the most important reason for their high efficiencies in OSCs. Our novel designed molecules exhibit red shift in absorption spectrum. Similarly, low excitation and binding energies of designed molecules offer improved power conversion efficiencies (PCEs) with highest possible charge photocurrent density (Jsc) in OSCs devices. Furthermore, study of PTB7‐Th/K1 complex is also done in order to examine charge transfer between within complex. By introducing the efficient end‐capped acceptor moieties in reference molecule, enhancement in charge mobilities is noted. The large open circuit voltage, low reorganizational energies, narrower highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, lower binding and excitation energies, and highly red shifting in absorption phenomenon indicate an efficient designing of molecules, which could be best fitted for high efficiency OSCs. Finally, theorized molecules are much superior related to their photovoltaic and electronic properties and thus are recommended to experimentalist for their synthesis and out‐looking future developments of highly efficient solar cells devices.

Non-fullerene acceptors with nitrogen-containing six-membered heterocycle cores for the applications in organic solar cells

Constructing unfused-core non-fullerene acceptors (NFAs) via intramolecular noncovalent interactions has been recognized as an effective route to obtain high-efficiency and low-cost concurrently for organic solar cells (OSCs). Herein, we report two new unfused-core NFAs, NCIC and NOCIC, with pyrazine and pyridazine as the cores, respectively. In contrast to traditional unfused-cores with fluorine or alkyloxy substituents, the nitrogen-containing six-membered heterocycle cores of NCIC and NOCIC have no substituents, which simplifies further synthetic steps of unfused-core NFAs. In the meantime, utilizing N⋯S and/or N⋯H interactions between the cores and adjacent cyclopentadithiophene (CPDT) units, NCIC and NOCIC own good π-conjugated backbone planarity, consequently, show intense absorptions from 550 nm to 800 nm. Moreover, the electronegativity of aromatic N atoms in the cores pulls down the highest occupied molecular orbital (HOMO) energy levels of the two NFAs, with -5.65 eV and -5.59 eV for NCIC and NOCIC, respectively, which is favorable for them to pair with the polymer donor with a deep HOMO level, PM6, to fabricate bulk-heterojunction (BHJ) OSCs. Finally, the PM6:NCIC based devices yield the best power conversion efficiency (PCE) of 10.32%, while those based on PM6:NOCIC blends provide a maximum PCE of 9.89%. This work demonstrates that the nitrogen-containing six-membered heterocycle is a kind of potential building block for high-performance and easy-synthesis unfused-core NFAs.

Preparation and characterization of quantum dot doped polyaniline photoactive film for organic solar cell application

Upconversion materials play a significant role in different applications like bio-imaging, solar cells, and therapy treatment due to their light conversion behavior (lower energy photon to higher energy photon). This material is a doping material for the improvement of the light-harvesting properties of polymers. However, there are limited publications in this field. Deposited/fabricated upconversion carbon quantum dot doped polyaniline photoactive film by electropolymerization. First, we prepared the quantum dot from the source of ascorbic acid and studied the quantum dot optical and structural properties by ultraviolet(UV), fluorescence (FL), and high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR), spectroscopy. The quantum dot is doped with polyaniline (PANI) using the fluorine-doped tin oxide (FTO) plate for making a film for this research. The prepared film has been analyzed spectroscopically for photophysical properties (absorption, transmission, band gap), surface morphology, and thermal stability of this merit to the solar cell. The current density and impedance spectra are have well supported by such a material characterization that might be used for the application of organic solar cells. Finally, the Förster resonance energy transfer of the quantum dot (donor) to the polyaniline (acceptor) is confirmed. With the help of the above characterization, results are supporting the organic solar cell.

A Facile Synthesized Polymer Featuring B‐N Covalent Bond and Small Singlet‐Triplet Gap for High‐Performance Organic Solar Cells

High-efficiency organic solar cells (OSCs) largely rely on polymer donors. Herein, we report a new building block BNT and a relevant polymer PBNT-BDD featuring B-N covalent bond for application in OSCs. The BNT unit is synthesized in only 3 steps, leading to the facile synthesis of PBNT-BDD. When blended with a nonfullerene acceptor Y6-BO, PBNT-BDD afforded a power conversion efficiency (PCE) of 16.1 % in an OSC, comparable to the benzo[1,2-b:4,5-b']dithiophene (BDT)-based counterpart. The nonradiative recombination energy loss of 0.19 eV was afforded by PBNT-BDD. PBNT-BDD also exhibited weak crystallinity and appropriate miscibility with Y6-BO, benefitting of morphological stability. The singlet-triplet gap (ΔEST ) of PBNT-BDD is as low as 0.15 eV, which is much lower than those of common organic semiconductors (≥0.6 eV). As a result, the triplet state of PBNT-BDD is higher than the charge transfer (CT) state, which would suppress the recombination via triplet state effectively.

A Facile Synthesized Polymer Featuring B‐N Covalent Bond and Small Singlet‐Triplet Gap for High‐Performance Organic Solar Cells

AbstractHigh‐efficiency organic solar cells (OSCs) largely rely on polymer donors. Herein, we report a new building block BNT and a relevant polymer PBNT‐BDD featuring B‐N covalent bond for application in OSCs. The BNT unit is synthesized in only 3 steps, leading to the facile synthesis of PBNT‐BDD. When blended with a nonfullerene acceptor Y6‐BO, PBNT‐BDD afforded a power conversion efficiency (PCE) of 16.1 % in an OSC, comparable to the benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based counterpart. The nonradiative recombination energy loss of 0.19 eV was afforded by PBNT‐BDD. PBNT‐BDD also exhibited weak crystallinity and appropriate miscibility with Y6‐BO, benefitting of morphological stability. The singlet–triplet gap (ΔEST) of PBNT‐BDD is as low as 0.15 eV, which is much lower than those of common organic semiconductors (≥0.6 eV). As a result, the triplet state of PBNT‐BDD is higher than the charge transfer (CT) state, which would suppress the recombination via triplet state effectively.

The Role of Carbon Quantum Dots in Organic Photovoltaics: A Short Overview

Carbon quantum dots (CDs) are a new class of fluorescent carbonaceous nanomaterials that were casually discovered in 2004. Since then, they have become object of great interest in the scientific community because of their peculiar optical properties (e.g., size-dependent and excitation wavelength-dependent fluorescence), which make them very similar to the well-known semiconductor quantum dots and suitable for application in photovoltaic devices (PVs). In fact, with appropriate structural engineering, it is possible to modulate CDs photoluminescence properties, band gap, and energy levels in order to realize the band matching suitable to enable the desired directional flow of charge carriers within the PV device architecture in which they are implanted. Considering the latest developments, in the present short review, the employment of CDs in organic photovoltaic devices (OPVs) will be summarized, in order to study the role played by these nanomaterials in the improvement of the performances of the devices. After a first brief summary of the strategies of structural engineering of CDs and the effects on their optical properties, the attention will be devoted to the recent highlights of CDs application in organic solar cells (OSCs) and in dye sensitized solar cells (DSSCs), in order to guide the users towards the full exploitation of the use of these nanomaterials in such OPV devices.