Prominent Free Charges Tunneling Through Organic Interlayer of 2D Perovskites

Abstract

The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden‐Popper (RP) and Dion‐Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4‐(2‐Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)2PbI4 and DJ (4AEPy)PbI4 from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH3, respectively. The interaction of N‐H···N hydrogen bond between adjacent organic molecules in (4AEPy)2PbI4 leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)2PbI4) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI4 are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI4 device displays better light response and X‐ray detection capability with a high sensitivity of 5627 µC Gyair‐1 cm‐2 and the lowest detectable dose rate of 20 nGyair s‐1.

Synthetic approaches for perovskite thin films and single-crystals

“…3). 86,87 This large exciton BE is much higher than the thermal energy at room temperature ( k B T = 25.7 meV). Therefore, the photogenerated electron and hole pairs in RP HPs are strongly bound together by coulombic attraction.…”

The rise of quasi-2D Dion–Jacobson perovskites for photovoltaics

“…For instance, Wei and co-workers reported that (4AEPy)PbI 4 (4AEPy 2+ , 4-(2-aminoethyl)pyridinium) presents a higher formation energy than (BDA)PbI 4 (BDA 2+ , 1,4-butanediamonium) and (HDA)PbI 4 (HDA 2+ , 1,6-hexamethylenediammonium), which could benefit the stability of the devices. 46…”

“…For instance, Wei and co-workers reported that (4AEPy)PbI 4 (4AEPy 2+ , 4-(2-aminoethyl)pyridinium) presents a higher formation energy than (BDA)PbI 4 (BDA 2+ , 1,4-butanediamonium) and (HDA)PbI 4 (HDA 2+ , 1,6-hexamethylenediammonium), which could benefit the stability of the devices. 46 Recent studies have revealed that ion migration (MA + , Pb 2+ , I À ) plays a significant role in the hysteresis and degradation in hybrid perovskite materials, and thus influences the long-term stability of PSCs. [47][48][49] An appreciable number of ions should move along the field direction under an electric or light field, creating vacancies/excess defects that act as charge recombination centers in perovskite films.…”

Light‐Induced Dielectric Enhancement in a 2D Dion–Jacobson Type Perovskite Phase Transition Material

“…For example, ( t ‐ACH) 2 (EA) 2 Pb 3 Br 10 (where t ‐ACH is 4‐aminomethyl‐1‐cyclohexanecarboxylate and EA is ethylammonium) exhibits successive phase transitions at 355 and 380 K. [ 16 ] In contrast, 2D Dion–Jacobson (DJ) type perovskites form direct connections instead of van der Waals forces between the adjacent inorganic slabs, and hydrogen bonded to the two terminal amino groups, which strengthens the structure stability of DJ‐type perovskites. [ 17,18 ] This merit endows 2D DJ‐type candidates’ stability with anti‐fatigue characteristics, being essential for their practical device applications, as verified by (BDA)(EA) 2 Pb 3 Br 10 [ 19 ] (where BDA is 1,4‐butadiammonium) and (AMP)(MA)Pb 2 I 7 [ 20 ] (where AMP is 4‐aminomethylpiperidinium and MA is methylammonium). However, the rigid perovskite structure of 2D DJ‐type perovskites with elimination of the van der Waals gap is unfavorable for phase transition and switchable dielectric property.…”