Highest Occupied Molecular Orbital Level Research Articles

A Linear Relationship between the Charge Transfer Amount and Level Alignment in Molecule/Two-Dimensional Adsorption Systems.

We systematically study the adsorption of tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) on a variety of two-dimensional (2D) monolayers with weak van der Waals (vdW) interactions based on density functional theory. We confirm that TTF can act as an effective donor when its highest occupied molecular orbital (HOMO) level is higher than the conduction band minimum (CBM) state of 2D materials, while TCNQ and TCNE can act as effective acceptors when their lowest unoccupied molecular orbital (LUMO) levels are lower than the valence band maximum (VBM) state of 2D materials. Moreover, our calculations reveal a linear relationship between the charge transfer amount and level alignment between the molecule and 2D monolayer. In other words, the charge transfer is linearly dependent on the energy difference between the HOMO level and 2D CBM state for the donor molecule or the energy difference between the LUMO level and 2D VBM state for the acceptor molecule. The linear relationship indicates that the charge transfer is insensitive to the local binding environments due to the weak vdW interaction. However, the linear relationship cannot be applied to atoms or molecules that are chemisorbed on 2D materials.

Observation of “Outlaw” Dual Aromaticity in Unexpectedly Stable Open-Shell Metal Clusters Caused by Near-Degenerate Molecular Orbital Coupling

The Huckel’s rule, Baird’s rule, and electronic shell closure model are classical and well-established concepts in chemistry, which have long been employed in rationalizing the aromaticity/antiarom...

Novel porphyrin polymers: synthesis and photoelectric property

A series of novel porphyrin monomers with different tail lengths were synthesized through the Alder–Longo method, and the corresponding polymers were successfully synthesized via radical polymerization. The structures of the porphyrin monomers and polymers were all depicted through proton nuclear magnetic resonance (1H-NMR) and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, and the photophysical and electrochemical properties were confirmed through UV–Vis spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The results showed that the polymers exhibited a deep highest occupied molecular orbital (HOMO) energy level and a large optical band gap, demonstrating their usefulness in photovoltaic devices. All of the porphyrin monomers formed a typical columnar phase, and the cleaning point of these porphyrin monomers reduced with the increasing length of the alkoxy tail chain. Thermogravimetric analysis demonstrated that the polymers had excellent thermal stability; the decomposition temperature was higher than 400 °C. The UV absorption spectrum of the polymers was between 400 and 670 nm. Compared with the absorption peak of the solution, the absorption peak after film formation presented a certain redshift. The HOMO level was lower than the stable critical level of the conjugated polymer in air (− 5.2 eV), indicating that the polymer is stable in air. In addition, the lowest unoccupied molecular orbital energy level was 0.49–0.64 eV, which was higher than that of the recipient PCBM, indicating that the polymers can be used as a donor material for solar cells.

Two Compatible Polymer Donors Enabling Ternary Organic Solar Cells with a Small Nonradiative Energy Loss and Broad Composition Tolerance

High‐performance nonfullerene ternary organic solar cells (OSCs) with two polymer donors are less frequently reported because of the limited numbers of efficient polymer donors with good compatibility. Herein, a wide‐bandgap polymer P1 with a deep‐lying highest occupied molecular orbital (HOMO) level is incorporated as the third component into the benchmark PM6:Y6 binary system to fabricate ternary OSCs. The introduction of P1 not only leads to extended absorption coverage and forms a cascade‐like energy level alignment but also shows excellent compatibility with PM6, resulting in a favorable morphology in the ternary blend. More importantly, P1 possesses a deeper HOMO level (−5.6 eV) than most well‐known donor polymers, which enables resulting ternary OSCs with an improved open‐circuit voltage. As a result, the optimized ternary OSCs with 40 wt% P1 in donors achieve a power conversion efficiency (PCE) of 16.2% with a small nonradiative recombination loss of 0.23 eV, which is among the highest values of ternary OSCs based on two polymer donors. In addition, the ternary OSCs show a broad composition tolerance with a high PCE of over 14% throughout the whole blend ratios. These results provide an effective approach to fabricate efficient ternary OSCs by synergizing two wide‐bandgap polymer donors.

Synthesis and characterization of a wide‐bandgap polymer based on perfluorinated and alkylthiolated benzodithiophene with a deep highest occupied molecular orbital level for organic photovoltaics

AbstractA perfluorinated and alkylthiolated benzodithiophene (BDT)‐ttTPD‐based donor polymer (P2FS‐ttTPD) was synthesized via a Stille polymerization, and found to have a number average molecular weight (Mn) of 13,000 g/mol (Đ = 2.3). P2FS‐ttTPD has a wide bandgap (1.96 eV) and a deep highest occupied molecular orbital (HOMO) level (−5.70 eV). The perfluorination and alkylthiolation of the polymer backbone lower the polymer's HOMO level significantly. The hole and electron mobilities of P2FS‐ttTPD were determined to be 1.12 × 10−4 and 9.38 × 10−7 cm2/V s, respectively. Polymer solar cell devices prepared with a P2FS‐ttTPD:IT‐4F (1:1) blend as the active layer were found to exhibit power conversion efficiencies of 4.15%, a short‐circuit current density (JSC) of 10.29 mA/cm2, an open‐circuit voltage (VOC) of 0.97 V, and a fill factor of 41.6%. The (1:1) blend devices were found to exhibit high VOC and low Eloss values.

Fine-tuning HOMO energy levels between PM6 and PBDB-T polymer donors via ternary copolymerization

To achieve high-efficiency polymer solar cells (PSCs), it is not only important to develop high-performance small molecule acceptors (SMAs) but also to find a matching polymer donor to achieve optimal morphology and matching electronic properties. Currently, state-of-the-art SMAs mostly rely on a donor polymer named PM6. However, as the family of SMAs continues to expend, PM6 may not be the perfect polymer donor due to the requirement of energy level matching. In this work, we tune the energy level of PM6via the strategy of ternary copolymerization. We achieve two donor polymers (named PL-1 and PL-2) with upshifted HOMO (the highest occupied molecular orbital) energy level (compared with PM6), and can thus match with the SMAs with upshifted HOMO energy levels compared with Y6. These two copolymers exhibit slightly higher order of molecular packing and similar charge transport properties, which demonstrate that the method of ternary copolymerization can fine tune the HOMO level of donor polymers, while the morphology and mobility of the blend film remain mostly unaffected. Among them, the best device based on PL-1: Y6 exhibits power conversion efficiencies (PCEs) of 16.37% with lower open circuit voltage (Voc) but higher short circuit current voltage (Jsc) and fill factor (FF) than that of the device based on PM6: Y6. This work provides an effective approach to find polymer matches for the SMAs with upshifted HOMO levels.

Evaluating the Role of Molecular Heredity in the Optical and Electronic Properties of Cross-Conjugated Benzo[1,2-d:4,5-d']bisoxazoles.

A series of eight benzo[1,2-d:4,5-d′]bisoxazole (BBOs) were synthesized using the heredity principle as a design motif, whereby we investigated which characteristics of the linear parents were inherited by their cross-conjugated children. Four linear parents bearing 4-tert-butylbenzene (P) or 1,3-bis(4-tert-butylphenyl)benzene (M) at either the 2,6- or 4,8-position on the BBO and four cross-conjugated children bearing various combinations of the two isoelectronic aryl substituents were evaluated. Due to the bulky nature of the M substituent compared to that of the P substituent, the influence of steric hindrance along the BBO axes was explored theoretically and experimentally. The optical and electronic properties of each molecule were investigated in the solution and solid state using density functional theory (DFT) and time-dependent DFT (TD-DFT) and characterized using ultraviolet photoelectron spectroscopy (UPS), ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence (PL) spectroscopy. The well-correlated theoretical and experimental results showed that the selective tuning of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels was possible through the strategic placement of substituents without impacting the H → L transition energy. Specifically, the theoretical results demonstrated that for the BBO children the HOMO and LUMO energy levels were inherited from the 4,8- and 2,6-parents, respectively. Each molecule was found to exhibit emission maxima ≤451 nm, making them ideal candidates for blue organic light-emitting diode (OLED) materials.

A Novel Wide‐Bandgap Polymer with Deep Ionization Potential Enables Exceeding 16% Efficiency in Ternary Nonfullerene Polymer Solar Cells

AbstractTernary strategies have attracted extensive attention due to their potential in improving power conversion efficiencies (PCEs) of single‐junction polymer solar cells (PSCs). In this work, a novel wide bandgap polymer donor (Egopt ≈ 2.0 eV) named PBT(E)BTz with a deep highest occupied molecular orbital (HOMO) level (≈−5.73 eV) is designed and synthesized. PBT(E)BTz is first incorporated as the third component into the classic PBDB‐T‐SF:IT‐4F binary PSC system to fabricate efficient ternary PSCs. A higher PCE of 13.19% is achieved in the ternary PSCs with a 5% addition of PBT(E)BTz over binary PSCs (12.14%). Similarly, addition of PBT(E)BTz improves the PCE for PBDB‐T:IT‐M binary PSCs from 10.50% to 11.06%. The study shows that the improved PCE in ternary PSCs is mainly attributed to the suppressed charge carrier recombination and more balanced charge transport. The generality of PBT(E)BTz as a third component is further evidenced in another efficient binary PSC system—PBDB‐TF:BTP‐4Cl: an optimized PCE of 16.26% is realized in the ternary devices. This work shows that PBT(E)BTz possessing a deep HOMO level as an additional component is an effective ternary PSC construction strategy toward enhancing device performance. Furthermore, the ternary device with 5% PBT(E)BTz displays better thermal and light stability over binary devices.

Benzo[b]selenophene/thieno[3,2-b]indole-Based N,S,Se-Heteroacenes for Hole-Transporting Layers.

Two series of new N,S,Se-heteroacenes, namely, 6H-benzo[4′,5′]selenopheno[2′,3′:4,5]thieno[3,2-b]indoles and 12H-benzo[4″,5″]selenopheno[2″,3″:4′,5′]thieno[2′,3′4,5]thieno[3,2-b]indoles, were successfully obtained using an effective strategy based on Fiesselmann thiophene and Fischer indole synthesis. The new molecules exhibit a large optical band gap (2.82 eV < Egopt < 3.23 eV) and their highest occupied molecular orbital (HOMO) energy formed by the plane π-core ranges between −5.2 and −5.6 eV, with the narrower optical band gap and lower HOMO level corresponding to selenated heteroacenes. In thin solid films of the heteroacenes, hole mobility measured using the conventional CELIV technique ranges between 10–5 and 10–4 cm2·V–1·s–1. All these make the proposed condensed-ring compounds a promising platform for the development of hole-transporting materials applicable in organic electronics.

Degradation of bromobenzene via external electric field

Bromobenzene is one of the organic pollutants that damage the natural environment and poses a serious threat to human health. Therefore, it is meaningful to study its degradation characteristics under the electric field. In this paper, density functional theory (DFT) at BPV86/6-311G (d, p) level are employed for the study of C–Br bond distance, total energy, charge distribution, dipole moment, lowest unoccupied molecular orbital (LUMO) level, highest occupied molecular orbital (HOMO) level, energy gap and potential energy surface (PES) of bromobenzene in external electric field ([Formula: see text]15.43[Formula: see text]V[Formula: see text][Formula: see text][Formula: see text]nm[Formula: see text]–15.43[Formula: see text]V[Formula: see text][Formula: see text][Formula: see text]nm[Formula: see text]). It shows that as the electric field increases, the C–Br bond tends to break. The changes in the HOMO level and the LUMO level result in a rapid drop in the energy gap. In addition, the dissociation barrier gradually decreases. When the applied electric field reaches 15.43[Formula: see text]V[Formula: see text][Formula: see text]nm[Formula: see text], the dissociation barrier disappears completely, which means that the C–Br bond is broken and bromobenzene is degraded.

Brightness enhancement of a direct-current-driven electroluminescent device prepared with zinc-sulfide powder

In this paper, we report an improved luminous efficiency of a direct-current-driven electroluminescent (EL) device using ZnS powder by controlling electron and hole injection barriers. The emission layer was fabricated by screen-printing of an EL paste using Cu-coated ZnS particles on a transparent conductive indium–tin-oxide electrode. The device was completed by stacking an Al thin film on the emission layer by thermal evaporation. We applied various forming voltages to investigate the current–voltage–luminescence characteristics of the device. An abrupt change in current during the forming process was caused by variation of the electron-blocking barrier toward the anode. The hole-injection barrier from the anode to the emission layer increased with the forming voltage. The obtained results indicated that the hole-injection barrier to the emission layer can be lowered by inserting materials with a low highest-occupied-molecular-orbital (HOMO) energy level between the anode and emission layer. We achieved a brightness enhancement of 29% by employing a thin film of poly-N-vinyl carbazole with a HOMO level of −5.6 eV as a hole-injection layer on the anode. We believe that the presented results will guide further studies for efficiency improvement of EL devices using powder particles applicable to next-generation lighting and displays.

Accurate Determination of the Minimum HOMO Offset for Efficient Charge Generation using Organic Semiconducting Alloys

AbstractCurrent research indicates that exciton dissociation into free charge carriers can be achieved in material combinations with the highest occupied molecular orbital (HOMO) offset lowered to 0 eV in non‐fullerene organic solar cells. However, the quantitative relationship between the HOMO offset and exciton dissociation has not been established because of the difficulty in achieving continuously tunable HOMO offsets. Here, the binary blends of PTQ10:ZITI‐S and PTQ10:ZITI‐N are combined to form the positive and negative HOMO offsets of 0.20 and −0.07 eV, respectively. While the PTQ10:ZITI‐S binary blend delivers a decent power conversion efficiency (PCE) of 10.69% with a short‐circuit current (Jsc) of 16.94 mA cm−2, the PTQ10:ZITI‐N with the negative offset shows a much lower PCE of 7.06% mainly because of the low Jsc of 12.03 mA cm−2. Because the tunable HOMO levels can be realized in organic semiconducting alloys based on ZITI‐N and ZITI‐S acceptors, the transformation of the HOMO energy offset from negative to positive values is achieved in the PTQ10:ZITIN:ZITI‐S ternary blends, delivering much‐improved PCEs up to 13.26% with a significant, 74% enhancement of Jsc to 20.93 mA cm−2. With detailed investigations, the study reveals that the minimum HOMO offset of ≈40 meV is required to achieve the most‐efficient exciton dissociation and photovoltaic performance.

Cyclohexane-cored dendritic host materials with high triplet energy for efficient solution-processed blue thermally activated delayed fluorescence OLEDs

Two dendritic host materials (CH-2D1 and CH-2D2) are developed by using non-conjugated cyclohexane core and two first/second generation carbazole dendrons, which show excellent solubility in organic solvents, high thermal stability and high triplet energy (ET) of 2.78–2.84 eV, making them suitable for fabrication of solution-processed blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Compared to CH-2D1 with the first-generation carbazole dendron which shows low-lying highest occupied molecular orbital (HOMO) energy level of −5.48 eV, CH-2D2 with the second-generation carbazole dendrons exhibits higher HOMO level of −5.37 eV, which is more favourable for hole injection from the anode to the emissive layers. Consequently, solution-processed blue TADF OLEDs utilizing CH-2D2 as host show promising device performance with a low turn-on voltage of 3.4 V, maximum external quantum efficiency of 17.8%, maximum luminous efficiency of 41.3 cd A−1 and power efficiency of 33.9 lm W−1, which can compare with the most efficient solution-processed blue TADF OLEDs based on small-molecule and polymer hosts. These results indicate that dendritic host materials with well-defined chemical structure and good solubility are an attractive approach―beyond the soluble small-molecule hosts and polymer hosts―for the development of efficient solution-processed TADF OLEDs.

A Fundamental Reason for the Need of Two Different Semiconductor Technologies for Complementary Thin-Film Transistor Operations

In this short commentary, we discuss a fundamental reason why two different semiconductor technologies are needed for complementary thin-film transistor (TFT) operations. It is mainly related to an energy-level matching between the band edge of the semiconductor and the work-function energy of the metal, which is used for the source and drain electrodes. The reference energy level is determined by the energy range of work-functions of typical metals for the source and drain electrodes. With the exception of silicon, both the conduction band edge (EC) and valence band edge (EV) of a single organic or inorganic material are unlikely to match the metal work-function energy whose range is typically from –4 to –6 eV. For example, typical inorganic materials, e.g., Zn–O, have the EC of around –4.5 eV (i.e., electron affinity), so the conduction band edge is within the range of the metal work-function energy, suggesting its suitability for n-channel TFTs. On the other hand, p-type inorganic materials, such as Cu–O, have an EV of around –5.5 eV, so the valence band edge is aligned with metal work-function energy, thus the usage for p-channel TFTs. In the case of p-type and n-type organic materials, their highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) should be aligned with metal work-function energy. For example, p-type organic material, e.g., pentacene, has a HOMO level around –5 eV, which is within the range of the metal work-function energy, implying usage for p-channel TFTs. However, its LUMO level is around –3 eV, not being aligned with the metals’ work-function energy. So it is hard to use pentacene for n-channel TFTs. Along with this, n-type organic materials (e.g., C60) should have HOMO levels within the typical metals’ work-function energy for the usage of n-channel TFT. To support this, we provide a qualitative and comparative study on electronic material properties, such as the electron affinity and band-gap of representative organic and inorganic materials, and the work-function energy of typical metals.

Difluorobenzoxadiazole-based conjugated polymers for efficient non-fullerene polymer solar cells with low voltage loss

Two donor-acceptor (D-A) conjugated copolymers based on difluorobenzoxadiazole (ffBX) and oligothiophenes, i.e. , PffBX-2T and PffBX-TT, were designed and synthesized for polymer solar cells (PSCs). Compared to the polymers based on difluorobenzothiadiazole (ffBT) units, the two ffBX-based polymers presented identical optical bandgaps (~1.62 eV), but lower highest occupied molecular orbital (HOMO) energy levels. Owing to the down-shifted HOMO levels, the PSCs based on PffBX-2T and PffBX-TT showed lower voltage loss, and the open-circuit voltage ( V oc ) was ~0.1 V higher than that of the devices with the ffBT-based polymer. As a result, higher photovoltaic performance was achieved for the devices based on the ffBX-based polymers. The power conversion efficiencies (PCEs) of the non-fullerene PSCs with PffBX-2T and PffBX-TT as the donor were 8.72% and 10.12%, respectively. The superior device performance of PffBX-TT resulted from the efficient exciton dissociation and charge transport as well as weak charge recombination, which could be ascribed to the favorable face-on packing of the conjugated backbones and the desired morphology in the blend film. Our study demonstrates that difluorobenzoxadiazole is a promising building block for constructing conjugated polymers for high-performance non-fullerene PSCs. • Difluorobenzoxadiazole-based polymers with alkylthiophene side chains were synthesized. • PffBX-2T and PffBX-TT based PSC devices showed low voltage loss of 0.54 and 0.52 V, respectively. • A high PCE up to 10.12% was achieved for PSC devices based on PffBX-TT.

Descriptors for Electrolyte-Renormalized Oxidative Stability of Solvents in Lithium-Ion Batteries.

Electrolyte stability against oxidation is one of the important factors limiting the development of high energy density batteries. The highest occupied molecular orbital (HOMO) level of solvent molecules has been traditionally used for understanding trends in their oxidative stability, but this assumes a noninteracting environment. However, solvent HOMO levels are renormalized because of molecules in their solvation shells. In this work, we first demonstrate an inexpensive and accurate method to determine the HOMO level of the solvent followed by simple descriptors for renormalization of the HOMO level due to different electrolyte components. The descriptors are based on Gutmann donor and acceptor numbers of the solvent and other components. The method uses fast generalized gradient approximation-level density functional theory calculations compared to previously used expensive, experimental data-dependent methods. This method can be used to screen for unexplored stable solvents among the large number of known organic compounds to design novel high-voltage stable electrolytes.

Asymmetric push-pull small molecules with auxiliary electron-accepting unit for bulk heterojunction organic solar cells

Two small molecular donors (TPA-DPP and TPA-DPP-MDN) were designed with asymmetric push-pull structure, namely, donor-acceptor (D-A) and donor-acceptor-acceptor (D-A-A) systems. They were synthesized and investigated by thermogravimetric analysis, UV–vis spectra, X-ray diffraction, density functional theory (DFT) calculation, electrochemical and the photovoltaic (PV) measurement. The D-A-A architecture (TPA-DPP-MDN) exhibited lower highest occupied molecular orbital (HOMO) of –5.18 eV, narrower optical band gap of 1.52 eV, better thermal stability and higher degree of ordered aggregation than these of the D-A system (TPA-DPP). TPA-DPP-MDN based PV device showed better performance with higher open-circuit voltage (VOC) and short-circuit current density (JSC) than these of TPA-DPP based PV devices due to the low-lying HOMO level and wide spectral absorption range of TPA-DPP-MDN.

Energy level tuning of aromatic polyamines by [2 + 2] cycloaddition-retroelectrocyclization for the optimization of device performances

The highest occupied molecular orbital (HOMO) level of hole-transporting polymeric materials was tuned by postfunctionalization based on a highly-efficient [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction. After the CA-RE reaction, the HOMO level of an aromatic polyamine, determined by the electrochemical first oxidation potential, was lowered from −5.30 eV to −5.37 eV. This enabled the smooth hole injection from the perovskite layer of organic-inorganic perovskite solar cells. Although the hole mobility of the aromatic polyamine, determined by the space-charge limited current (SCLC) method, decreased by this postfunctionalization, the energy level adjustment was more significant for the improvement of the solar cell performances. The device based on the postfunctionalized polyamine with the HOMO level of −5.37 eV showed more than twice the photoconversion efficiency than that based on the precursor polyamine with the HOMO level of −5.30 eV.

Linear Correlations between Adsorption Energies and HOMO Levels for the Adsorption of Small Molecules on TiO2 Surfaces

Adsorption is a fundamental step in catalysis on a solid surface, and therefore, its understanding is important for explaining its behavior. This work investigated the adsorption of various small molecules, including H2, N2, CO, CO2, CH4, NH3, H2O, H2S, dimethyl sulfoxide, alkanes, alkenes, alkynes, aromatic compounds, alcohols, aldehydes, ketones, nitriles, carboxylic acids, amides, and amines, on the anatase (101) and rutile (110) surfaces of TiO2, using periodic density functional theory calculations and statistical methods. Adsorption energies were computed at the same level of theory to obtain a clean and consistent data set. A linear relationship was observed between the adsorption energies of these molecules and their highest occupied molecular orbital (HOMO) levels, whereas no obvious correlation was evident for the lowest unoccupied molecular orbital levels. Improved correlations between the adsorption energies and HOMO levels were generated by dividing these molecules into two subgroups: hydrocarbons and heteroatom-containing compounds. Interactions between frontier molecular orbitals and the surfaces were considered, to gain a better understanding of the significant correlations that were identified. The data show that these relationships can be primarily ascribed to the interactions between the HOMO of the small molecule and conduction state of the TiO2 surface. The statistical analysis using machine learning demonstrated that the HOMO and dipole moment are the first and second most important properties, respectively, in terms of rationalizing and predicting the adsorption energies.

Double Acceptor Block-Containing Copolymers with Deep HOMO Levels for Organic Solar Cells: Adjusting Carboxylate Substituent Position for Planarity.

A deep highest occupied molecular orbital (HOMO) level is a prerequisite for polymer donor material to boost the organic solar cells (OSCs) performance by achieving high open circuit voltage ( Voc). Abandoning the traditional concept of donor-acceptor (D-A) structure, two copolymers PBTZ-4TC and PBTZ-C4T based on acceptor1-π-acceptor2 (A1-π-A2) architecture, where thiophene as the bridge, the difluorinated benzotriazole (BTZ) as A1 unit alternating copolymerized with 4,4'-dicarboxylate-substituted difluorotetrathiophene (4TC) and 3,3'-dicarboxylate-substituted difluorotetrathiophene (C4T) as A2, respectively, are developed. Because of the double acceptor blocks with high electron affinity, both A1-π-A2 type copolymers possess the lower HOMO levels of 5.52-5.56 eV, which are lower than most D-A type donors. Polymer PBTZ-4TC and PBTZ-C4T have the same backbone but only differ with the position of carboxylate substituent on the A2 unit. Intriguingly, subtle optimizing the position of the carboxylate-substitute causes a significantly difference on the properties of the A1-π-A2 type copolymers. PBTZ-C4T with more planar geometry is demonstrated with better light absorption, higher crystallinity, more pronounced temperature-dependent aggregation effect, and favorable bulk heterojunction morphology but with slightly higher HOMO level and more emission energy loss relative to the PBTZ-4TC. The PBTZ-C4T device exhibits the higher power conversion efficiency (PCE) of 9.34% than the PBTZ-4TC-based one (8.75%). These results reveal that concept of A1-π-A2 type copolymers not only can afford more flexibility in tuning the energy levels to achieve the deep HOMO levels but also can provide a facial strategy to greatly enrich the types of polymer donors for high-performance OSCs.