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.