and technologies in improving their charge-transport properties have been explored and practiced from molecular design, [9,10] synthetic method, [11,12] purification, [13,14] thin film microstructural optimization, [15,16] device configuration and fabrication, [17−20] to device interface engineering. [21−23] To be blunt, however, the carrier mobilities and device stability of polymer semiconductors nowadays are generally not adequate for the requirements of next-generation organic electronics. For example, the polymer semiconductors with carrier mobilities greater than 10 cm 2 V −1 s −1 are still few so far and almost all of them are thiophene-flanked diketopyrrolopyrrolebased copolymers (Table S1, Supporting Information). More importantly, the ambipolar or n-type polymer semiconductors with electron mobility exceeding 10 cm 2 V −1 s −1 are quite rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) and complementary metal-oxidesemiconductor-like circuits toward commercial high-grade electronics. [17,24−27] Nevertheless, the obtained fundamental understandings on charge-carrier transport mechanism in the exploring process still shows us invaluable guidelines for constructing high-mobility polymer semiconductors and PFETs. One fundamental understanding is "intrachain charge-carrier transport along the conjugated backbone chains is much faster than interchain charge-carrier transport, and the key limitation Polymer semiconductors with mobilities exceeding 10 cm 2 V −1 s −1 , especially ambipolar and n-type polymer semiconductors, are still rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) toward commercial high-grade electronics. Herein, two novel donor−acceptor copolymers, PNFFN-DTE and PNFFN-FDTE, are designed and synthesized based on the electron-deficient bisisoindigo (NFFN) and electron-rich dithienylethylenes (DTE or FDTE). The copolymer PNFFN-DTE, containing NFFN and DTE, possesses a partially locked polymeric conjugated backbone, whereas PNFFN-FDTE, containing NFFN and FDTE, has a fully locked one. Fluorine atoms in FDTE not only induce the formation of additional CH•••F hydrogen bonds, but also lower frontier molecular orbitals for PNFFN-FDTE. Both PNFFN-DTE and PNFFN-FDTE form more ordered molecular packing in thin films prepared from a polymer solution in bicomponent solvent containing 1,2-dichlorobenzene (DCB) and 1-chloronaphthalene (with volume ratio of 99.2/0.8) than pure DCB. The two copolymers-based flexible PFETs exhibit ambipolar charge-transport properties. Notably, the bicomponent solvent-processed PNFFN-FDTE-based PFETs afford a high electron mobility of 16.67 cm 2 V −1 s −1 , which is the highest electron-transport mobility for PFETs reported so far. The high electron mobility of PNFFN-FDTE is attributed to its fully locked conjugated backbone, dense molecular packing, and much matched LUMO energy level.

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA 0.8 Cs 0.2 PbI 3 , we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕμ), and carrier diffusion length (L D ) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of � 1.3 μs, high ϕμ of � 18.56 cm 2 V À 1 s À 1 , and long L D of � 7.85 μm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA 2 PbI 4 . This carrier diffusion length is comparable to that of some perovskite single crystals (> 5 μm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.

Molecular structures of hole transport materials (HTMs) have significant impact on the optoelectronic properties of perovskite/HTM heterojunction. But the structure–property relationship in the heterojunction remains poorly understood. By using poly­(3-alkylthiophene) (P3AT) as the HTM model, here we apply sum frequency generation vibrational spectroscopy to establish correlations among conformations of P3ATs, the hole extraction ability of P3ATs from the perovskite layer, and the charge mobility of P3ATs. It is revealed that with similar energy-level alignment, the conformational order of alkyl side chains in regioregular P3ATs can effectively regulate the hole extraction ability of P3ATs from perovskite layer by tuning reorganization energy. By contrast, the charge mobility of P3ATs strongly depends on the P3AT backbone’s coplanarity. Our findings decouple the roles of the long-hidden conformational order of alkyl side chain and the polythiophene backbone’s coplanarity on the performance of perovskite/HTM heterojunction, offering useful guidelines for boosting the performance of optoelectronic devices.

Constructing two-dimensional (2D)/three-dimensional (3D) organic–inorganic hybrid perovskite (OIHP) heterostructures is a promising strategy to simultaneously reduce defects and improve the stability of perovskite solar cells (PSCs). However, its regulating mechanism is not fully understood. In this study, we apply femtosecond time-resolved optical-pump terahertz-probe spectroscopy, supplemented by UV–vis absorption spectra measurements, to investigate charge-carrier dynamics of 2D/3D OIHP heterostructures and establish a correlation among effective charge-carrier mobility, hot-carrier cooling time, phonon frequency, and electronic disorder. We demonstrate that the electronic disorder dominates the charge-carrier dynamics during the heterojunction engineering in 2D/3D OIHPs and causes an exponential decrease in effective charge-carrier mobility and hot-carrier cooling time. The electronic disorder, quantitatively characterized by the Urbach energy, can offer an effective and general descriptor for evaluating the properties of 2D/3D hybrid perovskite materials. This work provides useful guidelines for boosting the performance of PSCs and optoelectronic devices by minimizing the Urbach energy.

Chemical modifications on aromatic spacers of 2D perovskites have been demonstrated to be an effective strategy to simultaneously improve optoelectronic properties and stability. However, its underlying mechanism is poorly understood. By using 2D phenyl‐based perovskites ([C6H5(CH2)mNH3]2PbI4) as models, the authors have revealed how the chemical nature of aromatic cations tunes the bandgap and charge transport of 2D perovskites by utilizing sum‐frequency generation vibrational spectroscopy to determine the stacking arrangement and orientation of aromatic cations. It is found that the antiparallel slip‐stack arrangement of phenyl rings between adjacent layers induces an indirect band gap, resulting in anomalous carrier dynamics. Incorporation of the CH2 moiety causes stacking rearrangement of the phenyl ring and thus promotes an indirect to direct bandgap transition. In direct‐bandgap perovskites, higher carrier mobility correlates with a larger orientation angle of the phenyl ring. Further optimizing the orientation angle by introducing a para‐substituted element in a phenyl ring, higher carrier mobility is obtained. This work highlights the importance of leveraging stacking arrangement and orientation of the aromatic cations to tune the photophysical properties, which opens up an avenue for advancing high‐performance 2D perovskites optoelectronics via molecular engineering.

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA 0.8 Cs 0.2 PbI 3 , we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕμ), and carrier diffusion length (L D ) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of � 1.3 μs, high ϕμ of � 18.56 cm 2 V À 1 s À 1 , and long L D of � 7.85 μm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA 2 PbI 4 . This carrier diffusion length is comparable to that of some perovskite single crystals (> 5 μm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.

Along with the development of narrow‐bandgap A–D–A and A–DA’D–A‐type small‐molecule acceptors (SMAs), polymer solar cells (PSCs) have witnessed a striking progress, with an impressing power conversion efficiency (PCE) approaching 20% recently. Aiming to realize the future commercial application of organic photovoltaic (OPV) technology, developing more efficient organic conjugated materials is urgently needed. Benefiting from the specific advantages in precisely adjusting the optoelectronic materials, random copolymerization strategy has drawn great attention during the past several years and has played a vital role in the development of PSCs. Herein, the functions of random copolymerization strategy in modulating the polymer properties are briefly discussed. Then the recent research progress of random copolymerization strategy of polymer photovoltaic materials in PSCs is reviewed. Finally, perspectives and a concise outlook on the further advancement of the random copolymerization strategy are put forward.

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