Highest Occupied Molecular Orbital Energy Level Research Articles

Utilizing a Carbazole‐Incorporated Regioisomeric Synthesis Strategy to Design Hole Transporting Materials for Perovskite Solar Cells

AbstractTwo new p‐type molecules, namely TAT‐TY3 and TAT‐TY4, featuring triazatruxene endcaps and carbazole π‐bridges, were synthesized. The photophysical and electrochemical properties of synthesized materials were comparatively investigated based on their 2,7‐ and 3,6‐carbazole conjugation pathways. Optical characterizations revealed the impact of non‐bonding electron delocalization of triazatruxene through carbazole moieties, resulting in a significant increase in absorption intensity corresponding to n‐π* energy transitions and a red shift of triazatruxene moieties. Consequently, the optical band gaps of TAT‐TY3 and TAT‐TY4 were measured at 3.0 and 3.2 eV, respectively. Moreover, the molecules′ first oxidation potentials exhibited a drastic difference due to the electrochemical behavior of 2,7‐ and 3,6‐carbazole moieties. The highest occupied molecular orbital (HOMO) level for TAT‐TY3 was measured to be −5.02 eV, while for TAT‐TY4, it was measured as −4.67 eV. Hole‐extraction properties were explored using steady‐state and time‐resolved photoluminescence spectroscopy, revealing enhanced charge transfer between the TAT‐TY3/Perovskite interface due to the better alignment of HOMO energy levels. The photovoltaic performances of the hole‐transporting materials (HTMs) were successfully characterized in triple‐cation perovskite solar cells and efficiencies of up to 17.9 %, 16.2 %, and 9.8 % were achieved for Spiro‐OMeTAD, TAT‐TY3, and TAT‐TY4, respectively.

Non-sacrificial anionic surfactant with high HOMO energy level as a general descriptor for zinc anode

Hydrogen evolution and dendrite growth severely plague the implementation of aqueous zinc-ion batteries. The electrolyte regulation strategy is powerful to alleviate the excrescent reactions of the electrolyte to Zn anode. However, there lacks effective electrolyte approaches for regulating stable and reversible Zn plating/stripping chemistry. Herein, we propose a general principle through evaluating the highest occupied molecular orbital (HOMO) energy level of molecules and employ it as a critical descriptor to select non-sacrificial anionic surfactant electrolyte additives for stabilizing Zn anodes. Benefiting from the high HOMO energy level, the excellent coordination and adsorption effects of the non-sacrificial surfactant additive renders the modulated solvation structure and dynamic molecule-enriched layer on the Zn anode, realizing sustainable regulation effect. The optimized electrolyte reduces water activity, uniforms Zn2+ flux, and stabilizes 3D ion diffusion near the anode/electrolyte interface, leading to the inhibited parasitic reactions and homogenous Zn nucleation and growth. Consequently, a stable and reversible Zn anode is obtained, represented by an ultralong cycling lifespan over 3200 h at 2 mA cm−2/2 mAh cm−2 and high coulombic efficiency of 99.75 %. This study provides a general guidance for screening optimal electrolyte additives for high-performance aqueous zinc-ion batteries.

Isothianaphthene quinoids: pyrazine-annelated structures for tuning electronic properties

Abstract The development of quinoidal systems with extended π-conjugation has elucidated the influence that diradical characteristics exert on structure–property relationships, which is significant because it broadens the possibilities for the use of organic semiconducting materials in organic electronics. However, the chain-length elongation of such quinoidal molecules has resulted in low chemical stability due to the large contribution of diradical characteristics and to the high level of the highest occupied molecular orbital (HOMO), both of which limit the synthesis of π-extended quinoidal molecules. Here, we describe solving this problem via aromatic stabilization. To accomplish this, we designed a system that utilizes electron-accepting pyrazine-fused thieno[3,4-b]pyrazine following the development of the isothianaphthene quinoids of thiophene 3-mer and 6-mer. Theoretical calculations indicate that the introduction of a pyrazine-annelated structure suppresses the diradical characteristics and stabilizes the HOMO energy level of quinoidal oligothiophenes. The thermal, photophysical, and physicochemical properties of newly synthesized quinoidal molecules with full annelation of the benzene and pyrazine rings were investigated. Quinoidal thiophene 3-mer functioned as an acceptor in organic solar cells with a power conversion efficiency of 1.04%. This study demonstrates that the introduction of pyrazine-fused rings is an effective molecular design to extend the chain length of quinoidal oligothiophenes.

Aqueous Processed All-Polymer Solar Cells with High Open-Circuit Voltage Based on Low-Cost Thiophene-Quinoxaline Polymers.

Eco-friendly solution processing and the low-cost synthesis of photoactive materials are important requirements for the commercialization of organic solar cells (OSCs). Although varieties of aqueous-soluble acceptors have been developed, the availability of aqueous-processable polymer donors remains quite limited. In particular, the generally shallow highest occupied molecular orbital (HOMO) energy levels of existing polymer donors limit further increases in the power conversion efficiency (PCE). Here, we design and synthesize two water/alcohol-processable polymer donors, poly[(thiophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-T)) and poly[(selenophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-Se)) with oligo(ethylene glycol) (OEG) side chains, having deep HOMO energy levels (∼-5.4 eV). The synthesis of the polymers is achieved in a few synthetic and purification steps at reduced cost. The theoretical calculations uncover that the dielectric environmental variations are responsible for the observed band gap lowering in OEG-based polymers compared to their alkylated counterparts. Notably, the aqueous-processed all-polymer solar cells (aq-APSCs) based on P(Qx8O-T) and poly[(N,N'-bis(3-(2-(2-(2-methoxyethoxy)-ethoxy)ethoxy)-2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-methyl)propyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-(2,5-thiophene)] (P(NDIDEG-T)) active layer exhibit a PCE of 2.27% and high open-circuit voltage (VOC) approaching 0.8 V, which are among the highest values for aq-APSCs reported to date. This study provides important clues for the design of low-cost, aqueous-processable polymer donors and the fabrication of aqueous-processable OSCs with high VOC.

Hyperbranched polyimide with triazole core structure for nonvolatile resistive switching memory

AbstractHyperbranched polyimides (HBPIs) possess a unique branched structure, which can make the lowest unoccupied molecular orbitals (LUMOs) degenerate and reduce the bandgap between the highest occupied molecular orbital (HOMO) and LUMO energy levels. The triazole group can facilitate the charge transfer process. Thus, a novel hyperbranched polyimide (HBPI‐TZA‐6FDA) has been prepared from new triazole derivative triamine monomer (TZA) and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) for memory device. The memory device with the structure ITO/HBPI‐TZA‐6FDA/Al exhibits a low‐threshold voltage of −2.2 V and a high ON/OFF current ratio of about 105. Meanwhile, the memory device shows nonvolatile write once read many times (WORM) type memory behavior and excellent stability with an operation time of 104 at a continuous applied voltage of −1 V. Optical, electrochemical experiments, and molecular simulation have been carried out to illustrate the memory performance. The memory performance is governed by the charge transfer between TZA and 6FDA units. The branched structure and triazole unit can reduce the band gap between HOMO and LUMO energy levels effectively, which is favorable for improving charge transfer and reducing threshold voltage. The HBPI‐TZA‐6FDA‐based memory device is favorable for memory device applications due to its relatively low‐power consumption and high‐operation stability.

Molecular understanding of electron donor influences in dye-sensitized solar cells of novel series-based D-A’-(π-A)2

The efficiency of the designed dye-sensitized solar cells (DSSCs) containing phenothiazine phenoxazine, and 5,10-dimethylphenazine as donors and triazine, phenyl with D-A’-(π-A)2 architecture has been examined utilizing Time-dependent (TD-DFT) and Density Functional Theory (DFT) techniques. The geometrical structures, electrical characteristics, absorption, and photovoltaic characteristics were studied using these techniques. Additionally, the computed findings show that various layouts can alter the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energy levels and reduce the energy gap between 1.63 and 2.30 eV. The absorption undergoes a redshift displacement. These bands are between 300 and 400 nm. This work aims at calculating the structural geometries and the electronic and optical properties of the designed dyes. In order to shed light on the bridging influence on geometric and TD-BHandH/6-31G(d) for optoelectronic properties, the density functional theory (DFT) and time-dependent TD-DFT at the B3LYP/6-31G(d) level were examined. Additionally, the complex [email protected] cluster's binding energies have been investigated.

New wide bandgap conjugated D-A copolymers based on Benzo[d]thiazole for efficient photovoltaics

Two wide bandgap copolymers based on benzo[d]thiazole unit, named PBTz-F and PBTz-Cl, containing benzo[1,2-b:4,5-b′]dithiophene (BDT) as electron donor units are developed. The resulting polymers lower the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels via substituting halogen atoms (fluorine or chlorine atoms) on the thiophene side chain of the BDT unit. However, the chlorine atom in the copolymers has a stronger capacity to downshift energy levels than the fluorine atom. PBTz-Cl:Y6-BO-based OSC delivers a higher PCE of 12.36% with simultaneously enhanced VOC of 0.90 V, JSC of 22.78 mA cm−2, and FF of 0.61 when compared to that based on PBTz-F:Y6-BO (PCE = 11.38%, JSC = 22.48 mA cm−2, VOC = 0.88 V, and FF = 0.58) due to its stronger absorption, higher charge mobilities, deeper HOMO energy level, and favorable blend film morphology. These results emphasized that chlorination is a practical strategy to obtain high PCE and BTz-based polymers are potential donor candidates for high-performance OSCs.

Trifluoromethylation in the Design and Synthesis of High-Performance Wide Bandgap Polymer Donors for Quasiplanar Heterojunction Organic Solar Cells.

New strategies for the molecular design to construct efficient electron-deficient units for D-A-type donor copolymers are urgently needed. Halogenation of electron-deficient units (A) has been shown to be the most effective strategy reported to date with which to produce high-performance donor polymers. Herein, we have constructed two different trifluoromethyl-substituted polymer donors, PBQP-CF3 and PBQ-CF3. The trifluoromethylation process typically involves complex protocols, which are not widely used in the synthesis of polymer donors. Accordingly, we have developed a single-step, one-pot synthesis of the new trifluoromethyl-substituted electron-deficient unit (A) of PBQ-CF3. The strong electron-withdrawing ability of the trifluoromethyl group ensures deeper highest occupied molecular orbital (HOMO) energy levels, and the non-covalent bonding interactions of the fluorine atoms are beneficial to the regulation of aggregation properties. Thus, both of the trifluoromethyl-substituted polymer donors obtained much higher power conversion efficiency (PCE) than PBDP-H (6.66%). PBQ-CF3 exhibits a deeper HOMO energy level, better aggregation behavior, and higher hole mobility than PBQP-CF3. PBQ-CF3-based quasiplanar heterojunction (Q-PHJ) devices therefore achieve simultaneously enhanced open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) and an impressive PCE (16.02%), which is much higher than that obtained by PBQP-CF3-based devices (12.57%). This work reveals a promising path to synthesis of the trifluoromethylation polymer donors and demonstrates that the trifluoromethylation strategy can be used to enhance the photovoltaic performance.

An effective strategy to design high-performance wide bandgap polymer donors for organic solar cells by increasing the backbone curvature

Although wide bandgap (WBG) polymer donors are widely used in non-fullerene organic solar cells (OSCs), only a few WBG polymers exhibited high power conversion efficiencies (PCEs). Developing WBG donors with ideal complementary absorption with narrow bandgap non-fullerene acceptors is critical to further improving the photovoltaic performance of OSCs. Here, we provide an effective strategy to widen the bandgap (Eg) of polymers by increasing the curvature of the polymer donor backbone structure and compare it with the fluorination strategy. Both experimental and theoretical results demonstrated that the fluorination strategy reduced the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PBDT-DT2FBT with little effect on the Eg. In contrast, the polymer PBDT-DTfBT, with a large backbone curvature, exhibited a reduced HOMO energy level and a significantly increased LUMO energy level, resulting in a significant increase in the optical Eg of 0.19 eV. The PBDT-DTfBT-based device achieved a high PCE of 15.89%, which far exceeded the PCEs of the PBDT-DTBT (9.84%) and PBDT-DT2FBT-based devices (8.02%). This work could guide the design of high-performance WBG donors.

Unveiling the effect of side chains and fluorination on the photovoltaic performance of D-A copolymers: a comparative study of P-HBT-T, P-FBT-T and P-FBT-O

Three random D-A copolymers containing thienopyrroledione (TPD) and benzodithiophene (BDT) named P-HBT-T, P-FBT-T, and P-FBT-O were synthesized. The effects of side chains on BDT and fluorination to benzothiadiazole on the photovoltaic performances of fabricated solar cells were investigated. The highest occupied molecular orbital (HOMO) levels of the polymers were −5.57, −5.51, and −5.65 eV for P-HBT-T, P-FBT-T, and P-FBT-O, respectively, suggesting low-lying HOMO energy levels. The optimized weight ratios of the polymer to PC71BM were determined as 1:2 with 24 mg/mL blend concentration for all polymers, and the maximum power conversion efficiencies (PCEs) of the devices were 7.35%, 7.76%, and 9.21% for P-HBT-T, P-FBT-T, and P-FBT-O, respectively, after optimizations with 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN). Trap-assisted recombination and bimolecular recombination loss mechanisms, which are PCE limiting mechanisms, were examined for all devices. The morphological and topographical properties were investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively. Our findings demonstrate that P-FBT-O-bearing organic solar cells (OSCs) emerged as the best-performing device due to their deeper HOMO level, high molecular weight, lower trap-assisted and bimolecular recombination, and superior morphology.

Design of novel organoboron small-molecule dyes based on dipolar nitrogen-boron-nitrogen unit for solution-processed photovoltaic devices

The nitrogen-boron-nitrogen (N–B–N) structure combined with strong polar B–N and B←N bonds simultaneously, opens a new window for the development of organoboron photovoltaic materials with narrow band gap and low highest occupied molecular orbital (HOMO) energy level. In this paper, two N–B–N-embedded blocks including boron dipyrromethane (BODIPY) and double B–N bridged bipyridyl (BNBP), are exploited to rationally regulate the band gap and energy level of the resulting material by virtue of their strong electron affinities. Thus, the thiophene as a weak electron-donating part is directly attached to strong electron-withdrawing BODIPY and BNBP respectively, giving much improved photoelectric properties for such simple push-pull architectures. To further improve photoelectric and thermal properties of the material, two novel extended D-π-A-π-D-type organoboron molecules namely BDPTPA and BNBPTPA, in which BODIPY and BNBP as strong electron-deficient core (A) connect strong electron-rich triphenylamine (D) via thiophene π-spacer, are synthesized by Stille reaction between BODIPY/BNBP and “π-D” segment. Therefore, BDPTPA exhibits a preferable electrochemical band gap as small as 1.36 eV close to near-infrared (NIR) region, which is one of the lowest values among the BODIPY-based small-molecule donors (SMDs). Furthermore, BNBPTPA shows stronger light absorption of up to 1.16 × 105 M−1 cm−1, deeper HOMO energy level of −5.28 eV and very excellent thermal stability (Td = 428 °C). It is mentioning that, BNBPTPA is first used as SMD material, blending with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) for solution-processed organic solar cell. Consequently, a reasonable power conversion efficiency (PCE) of 6.78% has been achieved with a satisfactory short-circuit density (Jsc) of 17.27 mA cm−2 and open-circuit voltage (Voc) of 0.87 V, which is the highest efficiency for BNBP-based SMDs so far. Our work demonstrates that a proposed molecular design and synthesis with dipolar N–B–N-containing unit and “π-D” fragment, can greatly broaden the types of new photovoltaic donor materials.

Balancing the Energy levels and Charge Mobility of the Conjugated Polymer PM6 by a Third Component to Enable Efficient Organic Solar Cells

AbstractThe notable wide bandgap conjugated polymer (WB‐CP) PM6 was optimized by introducing the third component of 4,8‐bis(tri‐iso‐propylsilicylethynyl)benzo[1,2‐b;4,5‐b’]dithiophene (BDT‐TIPS). With the increase of the BDT‐TIPS contents in the WB‐CPs, the maximal absorption peaks and on‐set‐band gap wavelengths of the WB‐CPs, are gradually blue‐shifted, alongside the successive deepening of the highest occupied molecular orbital (HOMO) from −5.54 eV to −5.68 eV. The more efficient OSCs with PCEs of 16.38 % were achieved in the OSCs from PM6‐TIPS5 paired with Y6 in contrast to that of 15.76 % for PM6 : Y6 based OSCs under AM1.5 sun stimulation (100 mA/cm2). Besides that, the investigations of the charge transporting, exciton dissociation and the recombination characteristics etc., were implemented and sugessted the improvement of the PCEs of PM6‐TIPS5 based OSCs was mainly ascribed to the subtly balancing of the HOMO energy levels and charge mobility of the PM6 by optimization of the feed ratio of the BDT‐TIPS.

Engineering of Hole Transporting Interface by Incorporating the Atomic-Precision Ag6 Nanoclusters for High-Efficiency Blue Perovskite Light-Emitting Diodes.

Properties of the underlying hole transport layer (HTL) play a crucial role in determining the optoelectronic performance of perovskite light-emitting devices (PeLEDs). However, endowing the current HTL system with a deep highest occupied molecular orbital (HOMO) level concurrent with high hole mobility is still a big challenge, in particular being an open constraint toward high-efficiency blue PeLEDs. In this regard, employing the poly(9-vinylcarbazole) as a model, we perform efficient incorporation of the atomic-precision metal nanoclusters (NCs), [Ag6PL6, PL = (S)-4-phenylthiazolidine-2-thione], to achieve significant tailoring in both HOMO energy level and hole mobility. As a result, the as-modified PeLEDs exhibit an external quantum efficiency (EQE) of 14.29% at 488 nm. The presented study exemplifies the success of metal NC involved HTL engineering and offers a simple yet effective additive strategy to settle the blue PeLED HTL dilemma, which paves the way for the fabrication of highly efficient blue PeLEDs.

Incorporating a weak acceptor unit into PTB7-Th to tune the open circuit voltage for non-fullerene polymer solar cells

PTB7-Th is one of the most effective polymer donors which have drawn huge attention in organic solar cells. However, the highest occupied molecular orbital (HOMO) level of PTB7-Th is relatively high, which limit open circuit voltage (Voc) of the cell devices. In this work, to develop the new members of PTB7-Th family materials with higher Vocs, two new random terpolymers PTB7-Th(0.9) and PTB7-Th(0.8) have been synthesized, in which contains 10% or 20% benzo[1,2-b:4,5-b′]dithiophene-2,6-dicarboxylate (VBDTC, a weak acceptor unit) moiety in PTB7-Th. It was found that the incorporating of VBDTC unit has great influence on optical and electronic properties of the related polymers. Comparison with PTB7-Th, the PTB7-Th(0.9) and PTB7-Th(0.8) exhibit blue shift in the UV−visible spectra, which forming a more complementary absorption with the low band gap non-fullerene acceptors, like ITIC and Y6. Increasing the percentage of VBDTC moiety, it can sufficiently deepen the low-lying HOMO level of the related polymers, which would expect to an enhancement in Voc. Non-fullerene solar cells blended with ITIC, PTB7-Th(0.9) exhibited a Voc of 0.839 V, with power conversion efficiency (PCE) of 4.86%. Interestingly, PTB7-Th(0.8) showed superior photovoltaic performance with a Voc of 0.862 V, and PCE of 5.24%. And when blended with Y6, the PCE of PTB7-Th(0.8) based device was further improved to 6.13%, due to increasing the short-circuit current (Jsc). The comprehensive study reveals that it is an effective strategy to tune the absorption spectra and deepens the HOMO energy level of the PTB7-Th related polymers by incorporation of a weak acceptor unit, thus, achieving higher Voc as well as photovoltaic performance.

Synthesis of D-A-Type Polymers Containing Thieno[3,2-b]thiophene Unit, Their Composites with Carbon, and Lithium Storage Performance as Anode Materials

Conjugated organic polymers have attracted extensive attention due to their light weight, mechanical flexibility, and structural diversity. However, poor electronic conductivity limits their application in the electrodes of lithium-ion batteries (LIBs). In this paper, two composites of D-A (donor-acceptor) polymer and activated carbon (AC)—PTPP@AC and PTPTD@AC—were designed and successfully prepared using thieno[3,2-b]thiophene (BTh) as the donor unit, benzo [1,2-b:6,5-b′] dithiophene-4,5-dione or 7a,11a-Dihydro-3,4-dithia-7,12-diaza[a,c]anthracene as the acceptor unit and AC as the substrate. PTPP@AC and PTPTD@AC were then studied as anode materials for LIBs. The successful preparation of the target products was demonstrated by FT-IR, Raman spectra, XRD, and XPS. Electrochemical properties, such as the specific capacity, cycling stability, and rate performance of the electrode materials, were tested by cyclic voltammetry and galvanostatic charge–discharge (GCD). The storage process of lithium ions was investigated by XPS and CV tests. Compared with PTPP@AC, PTPTD@AC had a higher reversible specific capacity (247.3 mAh g−1 after 300 cycles at 0.1 A g−1), a better rate performance (at 1 A g−1, specific capacity of 87.3 mAh g−1), and a higher long-term cycling performance (after 1000 cycles of 0.5 A g−1, the specific capacity remains at 146.6 mAh g−1). The better electrochemical performance of PTPTD compared to PTPP was due to the former’s significantly higher HOMO (highest occupied molecular orbital) energy level than that of PTPP, while the Eg of PTPTD was smaller than that of PTPP. The experimental results show that D-A conjugated polymers have great potential for applications as electrode materials for rechargeable batteries.

A potential sensor for assessing thorium (IV) based on Albuterol sulfate fluorescence enhancement: A density functional theory (DFT) study

• Introducing a new fluorescent sensor for assessing Th(IV) in environmental samples. • Fluorescence mechanism was discussed. • HOMO and LUMO energy levels has been calculated by DFT. This study introduces a potential fluorescence sensor for assessing thorium (Th(IV)) in aquatic environments. In the presence of Th(IV), Albuterol Sulfate ( ABS ) 4-[2-( tert -butylamino)-1-hydroxyethyl]-2-(hydroxymethyl)phenol; sulfuric acid exhibits significant fluorescence enhancement at 600 nm. The current ABS ligand sensor shows wide linear range from 6.0 × 10 −8 – 2.5 × 10 −7 mol/L and pH range of 4–6. Interestingly, when all evaluated interference ions coexisted, the change in fluorescence emission intensity of ABS -Th complex was roughly 2.3 %. The binding mode is studied and indicating a 2:1 complex formation between ABS ligand and Th (IV). Density functional theory (DFT) has been utilized to examine the interaction characteristics between the present ABS ligand sensor and Th(IV) and to compute the geometric configuration of the ABS and ABS -Th through the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The interaction properties exhibit considerable effect on the HOMO and LUMO properties of the complexes, as well as a fluorescence enhancement that could be attributable to the heavy atom effect of Th (IV). The ABS sensor shows remarkable features and provides good performance compared to some of the optical sensors, making it a potential new fluorescence sensor for Th(IV) assessment.

Edge carboxylation-induced charge separation dynamics of graphene quantum dot/cellulose nanocomposites

Graphene quantum dot (GQD)@cellulose nanocomposites possess optoelectronic properties of interest for photovoltaic applications. However, the optoelectronic properties related to the shapes and edge types of GQDs have not been fully explored. In the present work, we investigate the effects of carboxylation on the energy alignment and charge separation dynamics at the interface of GQD@cellulose nanocomposites using density functional theory calculations. Our results show that the GQD@cellulose nanocomposites composed of hexagonal GQDs with armchair edges exhibit better photoelectric performance than those composed of other types of GQDs. Carboxylation stabilizes the energy level of the highest occupied molecular orbital (HOMO) of the triangular GQDs with armchair edges but destabilizes the HOMO energy level of cellulose, resulting in hole transfer from the GQDs to cellulose upon photoexcitation. However, the calculated hole transfer rate is lower than the nonradiative recombination rate because excitonic effects dominate the dynamics of charge separation in GQD@cellulose nanocomposites.

Synergistic high efficiency and low energy loss of all-small-molecule organic solar cells based on benzotriazole-based π-bridge unit

Reducing energy loss (Vloss) is one of the most crucial challenges in organic photovoltaic cells. The Vloss, determined by the differences between the optical band gap (Eg) of the active layer material and the open-circuit voltage (Voc) of the device, is generally alleviated by lowering the energy difference between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) level of the donor (D) and acceptor (A). In this work, we synthesized two A-π-D-π-A-type small-molecule donors (SMDs) SM-benzotriazole (BTz)-1 and SM-BTz-2 by introducing a BTz π-bridge unit and terminal regulation. The BTz π-bridge unit significantly lowers the HOMO energy level of SMDs, resulting in high Voc and high mobility, achieving a balance of low energy loss (<0.5 eV) and high efficiency. Ultimately, the organic solar cells based on SM-BTz-2 as the donor and Y6 as the acceptor obtain a high Voc of 0.91 V, Jsc of 22.8 mA cm−2, fill factor of 68%, and power conversion efficiency (PCE) of 14.12%, which is one of the highest efficiencies based on the SMDs with triazole π-bridges to date. What’s more, the BTz π-bridge unit is a potential unit that can improve mobility and reduce energy loss.

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Synthesis of innovative triphenylamine-functionalized organic photosensitizers outperformed the benchmark dye N719 for high-efficiency dye-sensitized solar cells

Herein, we present a thorough photovoltaic investigation of four triphenylamine organic sensitizers with D–π–A configurations and compare their photovoltaic performances to the conventional ruthenium-based sensitizer N719. SFA-5–8 are synthesized and utilized as sensitizers for dye-sensitized solar cell (DSSC) applications. The effects of the donor unit (triphenylamine), π-conjugation bridge (thiophene ring), and various acceptors (phenylacetonitrile and 2-cyanoacetamide derivatives) were investigated. Moreover, this was asserted by profound calculations of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, the molecular electrostatic potential (MEP), and natural bond orbital (NBO) that had been studied for the TPA-sensitizers. Theoretical density functional theory (DFT) was performed to study the distribution of electron density between donor and acceptor moieties. The sensitization by the absorption of sensitizers SFA-5–8 leads to an obvious enhancement in the visible light absorption (300–750 nm) as well as a higher photovoltaic efficiency in the range of (5.53–7.56%). Under optimized conditions, SFA-7 showed outstanding sensitization of nanocrystalline TiO2, resulting in enhancing the visible light absorption and upgrading the power conversion efficiency (PCE) to approximately 7.56% over that reported for the N719 (7.29%). Remarkably, SFA-7 outperformed N719 by 4% in the total conversion efficiency. Significantly, the superior performance of SFA-7 could be mainly ascribed to the higher short-circuit photocurrents (Jsc) in parallel with larger open-circuit voltages (Voc) and more importantly, the presence of different anchoring moieties that could enhance the ability to fill the gaps on the surface of the TiO2 semiconductor. That could be largely reflected in the overall enhancement in the device efficiency. Moreover, the theoretical electronic and photovoltaic properties of all studied sensitizers have been compared with experimental results. All the 2-cyanoacrylamide derivative sensitizers demonstrated robust photovoltaic performance.