Reconfiguring the band-edge states of photovoltaic perovskites by conjugated organic cations

Abstract

The band edges of metal-halide perovskites with a general chemical structure of ABX3 (A, usually a monovalent organic cation; B, a divalent cation; and X, a halide anion) are constructed mainly of the orbitals from B and X sites. Hence, the structural and compositional varieties of the inorganic B–X framework are primarily responsible for regulating their electronic properties, whereas A-site cations are thought to only help stabilize the lattice and not to directly contribute to near-edge states. We report a π-conjugation–induced extension of electronic states of A-site cations that affects perovskite frontier orbitals. The π-conjugated pyrene-containing A-site cations electronically contribute to the surface band edges and influence the carrier dynamics, with a properly tailored intercalation distance between layers of the inorganic framework. The ethylammonium pyrene increased hole mobilities, improved power conversion efficiencies relative to that of a reference perovskite, and enhanced device stability.

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…[201][202][203][204] These spacers are typically insulating, although there is currently a strong incentive to make them electroactive to improve charge transport in optoelectronic devices. [205][206][207][208][209][210][211] The insulating layer of spacer molecules induces quantum and dielectric connement of electronic states in the metal halide octahedra. [212][213][214][215][216][217][218][219] Therefore, the bandgap, exciton binding and recombination dynamics can be changed by varying the number of metal halide octahedra, n, within each perovskite layer.…”

Using steric hindrance to manipulate and stabilize metal halide perovskites for optoelectronics

“…Very recently, Xue et al compared three conjugated organic cations, pyrene-based ammonium (PRA), pyrene-based methylammonium (PRMA) and pyrene-based ethylammonium (PREA). 36 They found that the A-site cations can modify the band-edge state of perovskites. PRA without alkyl chains has shallow interaction depth because of the steric hindrance from the pyrene group.…”

Fluoroethylamine Engineering for Effective Passivation to Attain 23.4% Efficiency Perovskite Solar Cells with Superior Stability

“…Organic‐inorganic hybrid perovskites, exhibiting large absorption coefficient, high carrier mobility, long carrier diffusion length, low exciton binding energy, and controllable optical band gap, [ 1–4 ] have been widely researched in terms of both scientific theory and photovoltaic applications, which has motivated the rapid development of the power conversion efficiency of perovskite solar cells (PSCs) in recent years. [ 5–15 ] However, they still suffer severely from the lack of long‐term durability. [ 11,16–18 ] Due to the different ion deposition speeds, defects are induced inevitably during the preparation process of perovskite films.…”

“…Passivating defects is an effective strategy to reduce charge non‐radiative recombination and improve the performance of PSCs. [ 10,17,19–21 ] The passivation can occur through various mechanisms, including coordination bonds, ionic bonds, and hydrogen bonds. Some larger organic cations, such as phenethylamine, polyethylenimine, and trifluoroethylamine, are widely employed to passivate defects.…”