Electronic Structures and Photoconversion Mechanism in Perovskite/Fullerene Heterojunctions

Abstract

It has been generally believed and assumed that organometal halide perovskites would form type II P–N junctions with fullerene derivatives (C60 or PCBM), and the P–N junctions would provide driving force for exciton dissociation in perovskite‐based solar cell. To the best of our knowledge, there is so far no experiment proof on this assumption. On the other hand, whether photogenerated excitons can intrinsically dissociate into free carrier in the perovskite without any assistance from a P–N junction is still controversial. To address these, the interfacial electronic structures of a vacuum‐deposited perovskite/C60 and a solution‐processed perovskite/PCBM junctions is directly measured by ultraviolet photoelectron spectroscopy. Contrary to the common believes, both junctions are found to be type I N–N junctions with band gap of the perovskites embedded by that of the fullerenes. Meanwhile, device with such a charge inert junction can still effectively functions as a solar cell. These results give direct experimental evidence that excitons are dissociated to free carriers in the perovskite film even without any assistance from a P–N junction.

Research Update: The electronic structure of hybrid perovskite layers and their energetic alignment in devices

“…With increasing C 60 coverage, an upward bending of the transport levels by 800 meV occurs accompanied by an upward shift of the perovskite DOS, indicating an electron transfer into the C 60 layer. Third, Lo et al 20 observed in their UPS measurements a staggered interface as shown in Fig. 6(c), so the LUMO of C 60 at the interface is positioned 340 meV above the perovskite CB, leading to an extraction barrier of 340 meV while the HOMO is below the VB of the perovskite, so no hole blocking should be achieved.…”

Ionic Charge Transfer Complex Induced Visible Light Harvesting and Photocharge Generation in Perovskite

“…14 However, there is so far little studies probing the chemical nature of the ions and how these ions pay their role in the photocharge generation. 3,15 Organometal trihalide perovskites have properties differ considerably from their constituting components. [16][17] For example, MAI and PbCl 2 are themselves wide energy gap semiconductors and therefore are electrically and optically inert.…”

Fullerol modification ferrihydrite for the degradation of acid red 18 under simulated sunlight irradiation

“…The initial pH value of the solution was adjusted using 0.1 M NaOH or HNO 3 . All experiments were carried out under constant stirring to ensure well dispersion of the samples.…”

“…Fh was prepared by slowly and simultaneously titrating Fe(NO 3 ) 3 (1 M, 40 mL) and NaOH (6 M, 20 mL) into 10 mL ultrapure water, with vigorous magnetic stirring and controlling the solution pH at 7 ± 0.2. After continuous magnetic stirring for another 30 min, the products were centrifuged and washed.…”

“…Fullerene (C 60 ) possesses unique electronic properties and has potential applications in a variety of areas, e.g., as photovoltaic and photocatalytic materials [1][2][3]. The excited state C 60 and its derivatives such as fullerol (polyhydroxyfullerene, PHF) are able to generate 1 O 2 , a selective oxidant useful in applications such as photocatalysis for wastewater treatment, through photosensitization [4][5][6][7].…”