Molecular Orbital Energy Levels Research Articles

Manipulating Alkyl Inner Side Chain of Acceptor for Efficient As-Cast Organic Solar Cells.

As-cast organic solar cells (OSCs) possess tremendous potential for low-cost commercial applications. Herein, five small-molecule acceptors (A1-A5) are designed and synthesized by selectively and elaborately extending the alkyl inner side chain flanking on the pyrrole motif to prepare efficient as-cast devices. As the extension of the alkyl chain, the absorption spectra of the films are gradually blue-shifted from A1 to A5 along with slightly uplifted lowest unoccupied molecular orbital energy levels, which is conducive for optimizing the trade-off between short-circuit current density and open-circuit voltage of the devices. Moreover, a longer alkyl chain improves compatibility between the acceptor and donor. The in situ technique clarifies that good compatibility will prolong molecular assembly time and assist in the preferential formation of the donor phase, where the acceptor precipitates in the framework formed by the donor. The corresponding film-formation dynamics facilitate the realization of favorable film morphology with a suitable fibrillar structure, molecular stacking, and vertical phase separation, resulting in an incremental fill factor from A1 to A5-based devices. Consequently, the A3-based as-cast OSCs achieve a top-ranked efficiency of 18.29%. This work proposes an ingenious strategy to manipulate intermolecular interactions and control the film-formation process for constructing high-performance as-cast devices.

Highly Sensitive and Selective Fluorescence and Smartphone-Based Sensor for Detection of Rutin Using Boron Nitrogen Co-doped Graphene Quantum Dots.

This research explores the fluorescence properties and photostability of boron nitrogen co-doped graphene quantum dots (BN-GQDs), evaluating their effectiveness as sensors for rutin (RU). BN-GQDs are biocompatible and exhibit notable absorbance and fluorescence characteristics, making them suitable for sensing applications. The study utilized various analytical techniques to investigate the chemical composition, structure, morphology, optical attributes, elemental composition, and particle size of BN-GQDs. Techniques included X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The average particle size of the BN-GQDs was determined to be approximately 3.5 ± 0.3nm. A clear correlation between the emission intensity ratio and RU concentration was identified across the range of 0.42 to 4.1μM, featuring an impressively low detection limit (LOD) of 1.23nM. The application of BN-GQDs as fluorescent probes has facilitated the development of a highly sensitive and selective RU detection method based on Förster resonance energy transfer (FRET) principles. This technique leverages emission at 465nm. Density Functional Theory (DFT) analyses confirm that FRET is the primary mechanism behind fluorescence quenching, as indicated by the energy levels of the lowest unoccupied molecular orbitals (LUMOs) of BN-GQDs and RU. The method's effectiveness has been validated by measuring RU concentrations in human serum samples, showing a recovery range between 97.8% and 103.31%. Additionally, a smartphone-based detection method utilizing BN-GQDs has been successfully implemented, achieving a detection limit (LOD) of 49nM.

High-Performance PM6:Y6-Based Ternary Solar Cells with Enhanced Open Circuit Voltage and Balanced Mobilities via Doping a Wide-Band-Gap Amorphous Acceptor.

Great progress has been made in organic solar cells (OSCs) in recent years, especially after the report of the highly efficient small-molecule electron acceptor Y6. However, the relatively low open circuit voltage (VOC) and unbalanced charge mobilities remain two issues that need to be resolved for further improvement in the performance of OSCs. Herein, a wide-band-gap amorphous acceptor IO-4Cl, which possessed a shallower lowest unoccupied molecular orbital (LUMO) energy level than Y6, was introduced into the PM6:Y6 binary system to construct a ternary device. The mechanism study revealed that the introduced IO-4Cl was alloyed with Y6 to prevent the overaggregation of Y6 and offer dual channels for effective hole transportation, resulting in balanced hole and electron mobilities. Taking these advantages, an enhanced VOC of 0.894 V and an improved fill factor of 75.58% were achieved in the optimized PM6:Y6:IO-4Cl-based ternary device, yielding a promising power conversion efficiency (PCE) of 17.49%, which surpassed the 16.72% efficiency of the PM6:Y6 binary device. This work provides an alternative solution to balance the charge mobilities of PM6:Y6-based devices by incorporating an amorphous high-performance LUMO A-D-A small molecule as the third compound.

Elevating Thermoelectric Performance by Compositing Dibromo-Substituted Thienoacene with SWCNTs.

Composites of organic small molecules (OSMs) and single-walled carbon nanotubes (SWCNTs) have drawn great attention as flexible thermoelectric (TE) materials in recent years. Here, we synthesized thieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA) and 2,6-dibromothieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA-2Br) and compounded them with SWCNTs, obtaining thermoelectric TTA/SWCNT and TTA-2Br/SWCNT composites. The introduction of the electron-withdrawing Br group was found to decrease the highest molecular orbital energy level and bandgap (Eg) of TTA-2Br. As a result, the Seebeck coefficient (S) and power factor (PF) of the OSM/SWCNT composite films were significantly improved. Moreover, suitable energy barrier between TTA-2Br and SWCNTs facilitates the energy filtering effect, which further enhances thermoelectric properties of the 40 wt % TTA-2Br/SWCNT composite film with optimum thermoelectric properties (PF = 242.59 ± 9.42 μW m-1 K-2 at room temperature), good thermal stability, and mechanical flexibility. In addition, the thermoelectric generator (TEG) prepared using 40 wt % TTA-2Br/SWCNT composite films and n-type SWCNT films can generate an output power of 102.8 ± 7.4 nW at a temperature difference of 20 °C. This work provides new insights into the preparation of OSM/SWCNT composites with significantly enhanced thermoelectric properties.

Design and Performance of Small-Molecule Donors with Donor-π-Acceptor Architecture Toward Vacuum-Deposited Organic Photovoltaics Having Heretofore Highest Short-Circuit Current Density.

The development of high-performance organic photovoltaic materials is of crucial importance for the commercialization of organic solar cells (OSCs). Herein, two structurally simple donor-π-conjugated linker-acceptor (D-π-A)-configured small-molecule donors with methyl-substituted triphenylamine as D unit, 1,1-dicyanomethylene-3-indanone as A unit, and thiophene or furan as π-conjugated linker, named DTICPT and DTICPF, are developed. DTICPT and DTICPF are facilely prepared via a two-step synthetic process with simple procedures. DTICPF with a furan π-conjugated linker exhibits stronger and broader optical absorption, deeper highest occupied molecular orbital (HOMO) energy levels, and better charge transport, compared to its thiophene analog DTICPT. As a result, vacuum-deposited OSCs based on DTICPF: C70 show an impressive power conversion efficiency (PCE) of 9.36% (certified 9.15%) with short-circuit current density (Jsc) up to 17.49mA cm-2 (certified 17.56mA cm-2), which is the highest Jsc reported so far for vacuum-deposited OSCs. Besides, devices based on DTICPT: C70 and DTICPF: C70 exhibit excellent long-term stability under different aging conditions. This work offers important insights into the rational design of D-π-A configured small-molecule donors for high efficient and stable vacuum-deposited OSCs.

Wide Bandgap Polymer Donors Based on Succinimide-Substituted Thiophene for Nonfullerene Organic Solar Cells.

The advent of nonfullerene acceptors (NFAs) has greatly improved the photovoltaic performance of organic solar cells (OSCs). However, to compete with other solar cell technologies, there is a pressing need for accelerated research and development of improved NFAs as well as their compatible wide bandgap polymer donors. In this study, a novel electron-withdrawing building block, succinimide-substituted thiophene (TS), is utilized for the first time to synthesize three wide bandgap polymer donors: PBDT-TS-C5, PBDT-TSBT-C12, and PBDTF-TSBT-C16. These polymers exhibit complementary bandgaps for efficient sunlight harvesting and suitable frontier energy levels for exciton dissociation when paired with the extensively studied NFA, Y6. Among these donors, PBDTF-TSBT-C16 demonstrates the highest hole mobility and a relatively low highest occupied molecular orbital (HOMO) energy level, attributed to the incorporation of thiophene spacers and electron-withdrawing fluorine substituents. OSC devices based on the blend of PBDTF-TSBT-C16:Y6 achieve the highest power conversion efficiencyof 13.21%, with a short circuit current density (Jsc) of 26.83mA cm-2, an open circuit voltage (Voc) of 0.80V, and a fill factorof 0.62. Notably, the Voc × Jsc product reaches 21.46mW cm-2, demonstrating the potential of TS as an electron acceptor building block for the development of high-performance wide bandgap polymer donors in OSCs.

Nitrogen-Embedding Strategy for Short-Range Charge Transfer Excited States and Efficient Narrowband Deep-Blue Organic Light Emitting Diodes.

The development of deep-blue organic light-emitting diodes (OLEDs) featuring high efficiency and narrowband emission is of great importance for ultrahigh-definition displays with wide color gamut. Herein, based on the nitrogen-embedding strategy for modifying the short range charge transfer excited state energies of multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters, we introduce one or two nitrogen atoms into the central benzene ring of a versatile boron-embedded 1,3-bis(carbazol-9-yl)benzene skeleton. This approach resulted in the stabilization of the highest occupied molecular orbital energy levels and the formation of intramolecular hydrogen bonds, and thus systematic hypsochromic shifts and narrowing spectra. In toluene solution, two heterocyclic-based MR-TADF molecules, Py-BN and Pm-BN, exhibit deep-blue emissions with high photoluminescence quantum yields of 93% and 94%, and narrow full width at half maximum of 14 and 13 nm, respectively. A deep-blue hyperfluorescent OLED based on Py-BN exhibited a maximum external quantum efficiency of 27.7% and desired color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.150, 0.052). These results demonstrate the significant potential for the development of deep blue narrowband MR-TADF emitters.

Nitrogen‐Embedding Strategy for Short‐Range Charge Transfer Excited States and Efficient Narrowband Deep‐Blue Organic Light Emitting Diodes

The development of deep‐blue organic light‐emitting diodes (OLEDs) featuring high efficiency and narrowband emission is of great importance for ultrahigh‐definition displays with wide color gamut. Herein, based on the nitrogen‐embedding strategy for modifying the short range charge transfer excited state energies of multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitters, we introduce one or two nitrogen atoms into the central benzene ring of a versatile boron‐embedded 1,3‐bis(carbazol‐9‐yl)benzene skeleton. This approach resulted in the stabilization of the highest occupied molecular orbital energy levels and the formation of intramolecular hydrogen bonds, and thus systematic hypsochromic shifts and narrowing spectra. In toluene solution, two heterocyclic‐based MR‐TADF molecules, Py‐BN and Pm‐BN, exhibit deep‐blue emissions with high photoluminescence quantum yields of 93% and 94%, and narrow full width at half maximum of 14 and 13 nm, respectively. A deep‐blue hyperfluorescent OLED based on Py‐BN exhibited a maximum external quantum efficiency of 27.7% and desired color purity with Commission Internationale de L’Eclairage (CIE) coordinates of (0.150, 0.052). These results demonstrate the significant potential for the development of deep blue narrowband MR‐TADF emitters.

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.

Surface Passivation of Perovskite by Hole‐Blocking Layer toward Efficient and Stable Inverted Solar Cells

Inverted (p‐i‐n) perovskite solar cells (PSCs) are advantageous in terms of easy fabrication, low‐temperature processibility, negligible hysteresis, and excellent compatibility with the tandem devices in comparison with the regular (n‐i‐p) counterparts. Hole‐blocking layer is crucial for efficient electron transport of inverted PSCs, and only a single hole‐blocking layer of bathocuproine (BCP) is used typically. Herein, bis[2‐(diphenylphosphino)phenyl] ether oxide (DPEPO) with a deep highest occupied molecular orbital (HOMO) energy level is incorporated atop of perovskite film as an auxiliary hole‐blocking layer, resulting in an enhanced electron transport of inverted PSC devices. The P=O group within DPEPO can coordinate with Pb2+ cations of perovskite, leading to passivation of surface defects of perovskite. Besides, incorporation of DPEPO hole‐blocking layer prohibits undesired hole transport from perovskite to PCBM electron transport layer (ETL), thus suppressing non‐radiative electron–hole recombination. As a result, combined with BCP hole‐blocking layer, inverted PSC devices based on double hole‐blocking layers exhibit a decent power conversion efficiency (PCE) of 24.17% with a high open‐circuit voltage (Voc) of 1.15 V which dramatically surpasses that based on single hole‐blocking layer (22.26%). Moreover, incorporation of hydrophobic DPEPO helps to improve the ambient and thermal stabilities of inverted PSC devices.

Hückel molecular orbital theory on a quantum computer: A scalable system-agnostic variational implementation with compact encoding.

Hückel molecular orbital (HMO) theory provides a semi-empirical treatment of the electronic structure in conjugated π-electronic systems. A scalable system-agnostic execution of HMO theory on a quantum computer is reported here based on a variational quantum deflation (VQD) algorithm for excited state quantum simulation. A compact encoding scheme is proposed here that provides an exponential advantage over the direct mapping and allows for quantum simulation of the HMO model for systems with up to 2n conjugated centers with n qubits. The transformation of the Hückel Hamiltonian to qubit space is achieved by two different strategies: an iterative refinement transformation and the Frobenius-inner-product-based transformation. These methods are tested on a series of linear, cyclic, and hetero-nuclear conjugated π-electronic systems. The molecular orbital energy levels and wavefunctions from the quantum simulation are in excellent agreement with the exact classical results. However, the higher excited states of large systems are found to suffer from error accumulation in the VQD simulation. This is mitigated by formulating a variant of VQD that exploits the symmetry of the Hamiltonian. This strategy has been successfully demonstrated for the quantum simulation of C60 fullerene containing 680 Pauli strings encoded on six qubits. The methods developed in this work are easily adaptable to similar problems of different complexity in other fields of research.

Pushing the Limit of Photo-Controlled Polymerization: Hyperchromic and Bathochromic Effects.

The photocatalyst (PC) zinc tetraphenylporphyrin (ZnTPP) is highly efficient for photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. However, ZnTPP suffers from poor absorbance of orange light by the so-called Q-band of the absorption spectrum (maximum absorption wavelength λmax = 600 nm, at which molar extinction coefficient εmax = 1.0×104 L/(mol·cm)), hindering photo-curing applications that entail long light penetration paths. Over the past decade, there has not been any competing candidate in terms of efficiency, despite a myriad of efforts in PC design. By theoretical evaluation, here we rationally introduce a peripheral benzo moiety on each of the pyrrole rings of ZnTPP, giving zinc tetraphenyl tetrabenzoporphyrin (ZnTPTBP). This modification not only enlarges the conjugation length of the system, but also alters the a1u occupied π molecular orbital energy level and breaks the accidental degeneracy between the a1u and a2u orbitals, which is responsible for the low absorption intensity of the Q-band. As a consequence, not only is there a pronounced hyperchromic and bathochromic effect (λmax = 655 nm and εmax = 5.2×104 L/(mol·cm)) of the Q-band, but the hyperchromic effect is achieved without increasing the intensity of the less useful, low wavelength absorption peaks of the PC. Remarkably, this strong 655 nm absorption takes advantage of deep-red (650-700 nm) light, a major component of solar light exhibiting good atmosphere penetration, exploited by the natural PC chlorophyll a as well. Compared with ZnTPP, ZnTPTBP displayed a 49% increase in PET-RAFT polymerization rate with good control, marking a significant leap in the area of photo-controlled polymerization.

All chlorination strategy on end-group of guest acceptor enables 18.39 % efficiency and high VOC for ternary organic solar cells

The ternary strategy has been proven to be an effective method to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, a new non-fullerene fused-ring acceptor (BTMe-8Cl) with 3,8-dimethylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTMe) core and all chlorination end-group (4,5,6,7-tetrachloro-1H-indene-1,3(2H)-dione) is synthesized and incorporated as a guest electron acceptor in PM6:Y6:BTMe-8Cl ternary system. The addition of BTMe-8Cl effectively improves the open-circuit voltage (VOC) of the ternary OSCs due to the higher lowestunoccupied molecular orbital (LUMO) energy level of BTMe-8Cl than that of Y6. Fine-tuning the proportion of BTMe-8Cl in ternary OSCs results in the optimal phase separations in the ternary films. Finally, an excellent PCE of 18.39 % and a VOC of 0.896 V are achieved for the ternary OSCs based on PM6:Y6:BTMe-8Cl (1:1.2:0.2). Especially, the VOC of 0.896 V is the highest value for PM6:Y6 system up to now.

Mapping the correlations between bandgap, HOMO, and LUMO trends for meta substituted Zn-MOFs.

Bandgap is a key property that determines electrical and optical properties in materials. Modulating the bandgap thus is critical in developing novel materials particularly semiconductors with improved features. This study examines the bandgap, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energy level trends in a metal organic framework, metal-organic framework 5 (MOF-5), as a function of Hammett substituent effect (with the constant σm in the meta-position of the benzene ring) and solvent dielectric effect (with the constant ε). Specifically, experimental design and response surface methodologies helped to assess the significance of trends and correlations between these molecular properties with σm and ε. While the HOMO and LUMO decrease with increasing σm, the LUMO exhibits greater sensitivity to the substituent's electron withdrawing capability. The relative difference in these trends helps to explain why the bandgap tends to decrease with increasing σm.

Acceptor molecules with Carbon–Carbon singly bonded central and terminal units for efficient P3HT-based organic solar cells

Herein, we synthesized two small molecules named as 4TBTCN and 6TBTCN with strongly electron-rich 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydrothieno[3′,2′:4,5]cyclopenta[1,2-b]thieno[2″,3′′:3′,4′]cyclopenta[1′,2′:4,5]thieno[2,3-d]thiophene or 6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrothieno[2″,3′′:4′,5′]thieno[3′,2′:4,5]cyclopenta[1,2-b]thieno[2‴,3‴:4″,5′′]thieno[2″,3′′:3′,4′]cyclopenta[1′,2′:4,5]thieno[2,3-d]thiophene as central unit and weak electron-withdrawing benzo[c] [1,2,5] thiadiazole-4-carbonitrile as termini, which were connected by C–C single bond. Both molecules exhibited medium optical bandgap and high-lying frontier molecular orbital energy levels, which were matched with those of the representative low-cost polymer donor P3HT. Moreover, 4TBTCN and 6TBTCN showed high stability under continuous illumination and base condition, owing to a lack of exocyclic vinyl group between the central unit and end group. Compared to P3HT:6TBTCN, P3HT:4TBTCN blend system displayed lower miscibility and thus more distinct phase separation, leading to more efficient charge transport and collection. Although the LUMO energy level of 4TBTCN was 0.15 eV deeper than that of 6TBTCN, the energy loss for P3HT:4TBTCN based device was similar to that of P3HT:6TBTCN based device. As a result, P3HT:4TBTCN based device displayed a similar open-circuit voltage but higher fill factor and short-circuit current density, yielding a superior power conversion efficiency, in comparison to P3HT:6TBTCN based device. This work provides a new strategy for design of efficient and stable acceptor molecules.

An Asymmetric Coumarin-Anthracene Conjugate as Efficient Fullerene-Free Acceptor for Organic Solar Cells.

Asymmetric wide-bandgap fullerene-free acceptors (FFAs) play a crucial role in organic solar cells (OSCs). Here, we designed and synthesized a simple asymmetric coumarin-anthracene conjugate named CA-CN with optical bandgap of 2.1 eV in a single-step condensation reaction. Single crystal X-ray structure analysis confirms various multiple intermolecular non-covalent interactions. The molecular orbital energy levels of CA-CN estimated from cyclic voltammetry were found to be suitable for its use as an acceptor for OSCs. Binary OSCs fabricated using CA-CN as acceptor and PTB7-Th as the donor achieve a power conversion efficiency (PCE) of 11.13%. We further demonstrate that the insertion of 20 wt% of CA-CN as a third component in ternary OSCs with PTB7-Th:DICTF as the host material achieved an impressive PCE of 14.91%, an improvement of ~43% compared to the PTB7-Th:DICTF binary device (10.38%). Importantly, the ternary blend enhances the absorption coverage from 400 to 800 nm and improves the morphology of the active layer. The findings highlight the efficacy of an asymmetric design approach for FFAs, which paves the way for developing high-efficiency OSCs at low cost.

An Asymmetric Coumarin‐Anthracene Conjugate as Efficient Fullerene‐Free Acceptor for Organic Solar Cells

Asymmetric wide‐bandgap fullerene‐free acceptors (FFAs) play a crucial role in organic solar cells (OSCs). Here, we designed and synthesized a simple asymmetric coumarin‐anthracene conjugate named CA‐CN with optical bandgap of 2.1 eV in a single‐step condensation reaction. Single crystal X‐ray structure analysis confirms various multiple intermolecular non‐covalent interactions. The molecular orbital energy levels of CA‐CN estimated from cyclic voltammetry were found to be suitable for its use as an acceptor for OSCs. Binary OSCs fabricated using CA‐CN as acceptor and PTB7‐Th as the donor achieve a power conversion efficiency (PCE) of 11.13%. We further demonstrate that the insertion of 20 wt% of CA‐CN as a third component in ternary OSCs with PTB7‐Th:DICTF as the host material achieved an impressive PCE of 14.91%, an improvement of ~43% compared to the PTB7‐Th:DICTF binary device (10.38%). Importantly, the ternary blend enhances the absorption coverage from 400 to 800 nm and improves the morphology of the active layer. The findings highlight the efficacy of an asymmetric design approach for FFAs, which paves the way for developing high‐efficiency OSCs at low cost.

Enhancement of thermoelectric performance of thienoisoindigo based D‐A conjugated polymers through the incorporation of 3,4‐ethylenedioxythiophene as donor unit

AbstractWith the good planarity of conjugated backbone and high charge carrier mobilities, thienoisoindigo (TIIG)‐based polymers show great potential in organic electronic devices. In this work, two TIIG‐based D‐A conjugated polymers (PTIIG‐3T and PTIIG‐2T‐EDOT) were designed and synthesized, which exhibit high lying highest occupied molecular orbital (HOMO) energy level and can be facilely doped by FeCl3. Compared with PTIIG‐3T, one thiophene unit in the donor building block is replaced by 3,4‐ethylenedioxythiophene (EDOT) in PTIIG‐2T‐EDOT, and PTIIG‐2T‐EDOT shows a higher HOMO level with slightly higher coplanarity than PTIIG‐3T, which induce an enhancement in electrical conductivity after oxidation doping. After proper doping, doped PTIIG‐2T‐EDOT film achieved a higher TE power factor of 17.9 μW m−1 K−2 than that of PTIIG‐3T due to its higher conductivity. The results indicate that TIIG unit is a promising building block for future high‐performance conjugated polymers for thermoelectric applications, and incorporation of the EDOT unit into D‐A conjugated polymers could be an effective way to develop high performance thermoelectric polymers.

Dipole Moments Regulation of Biphosphonic Acid Molecules for Self-assembled Monolayers Boosts the Efficiency of Organic Solar Cells Exceeding 19.7.

PSS has been widely used as a hole extraction layer (HEL) in organic solar cells (OSCs). However, their acidic nature can potentially corrode the indium tin oxide (ITO) electrode over time, leading to adverse effects on the longevity of the OSCs. Herein, we have developed a class of biphosphonic acid molecules with tunable dipole moments for self-assembled monolayers (SAMs), namely, 3-BPIC(i), 3-BPIC, and 3-BPIC-F, which exhibit an increasing dipole moment in sequence. Compared to centrosymmetric 3-BPIC(i), the axisymmetric 3-BPIC and 3-BPIC-F exhibit higher adsorption energies (Eads) with ITO, shorter interface spacing, more uniform coverage on ITO surface, and better interfacial compatibility with the active layer. Thanks to the incorporation of fluorine atoms, 3-BPIC-F exhibits a deeper highest occupied molecular orbital (HOMO) energy level and a larger dipole moment compared to 3-BPIC, resulting in an enlarged work function (WF) for the ITO/3-BPIC-F substrate. These advantages of 3-BPIC-F could not only improve hole extraction within the device but also lower the interfacial impedance and reduce nonradiative recombination at the interface. As a result, the OSCs using SAM based on 3-BPIC-F obtained a record high efficiency of 19.71%, which is higher than that achieved from the cells based on 3-BPIC(i) (13.54%) and 3-BPIC (19.34%). Importantly, 3-BPIC-F-based OSCs exhibit significantly enhanced stability compared to that utilizing PEDOT:PSS as HEL. Our work offers guidance for the future design of functional molecules for SAMs to realize even higher performance in organic solar cells.

Improvement of Perovskite Solar Cells Efficiency by Management of the Electron Withdrawing Groups in Hole Transport Materials: Theoretical Calculation and Experimental Verification.

Management of functional groups in hole transporting materials (HTMs) is a feasible strategy to improve perovskite solar cells (PSCs) efficiency. Therefore, starting from the carbazole-diphenylamine-based JY7 molecule, JY8 and JY9 molecules are incorporated into the different electron-withdrawing groups of fluorine and cyano groups on the side chains. The theoretical results reveal that the introduction of electron-withdrawing groups of JY8 and JY9 can improve these highest occupied molecular orbital(HOMO)energy levels, intermolecular stacking arrangements, and stronger interface adsorption on the perovskite. Especially, the results of molecular dynamics (MD) indicate that the fluorinated JY8 molecule can yield a preferred surface orientation, which exhibits stronger interface adsorption on the perovskite. To validate the computational model, the JY7-JY9 are synthesized and assembled into PSC devices. Experimental results confirm that the HTMs of JY8 exhibit outstanding performance, such as high hole mobility, low defect density, and efficient hole extraction. Consequently, the PSC devices based on JY8 achieve a higher PCE than those of JY7 and JY9. This work highlights the management of the electron-withdrawing groups in HTMs to realize the goal of designing HTMs for the improvement of PSC efficiency.