Highly Planar Benzodipyrrole‐Based Hole Transporting Materials with Passivation Effect for Efficient Perovskite Solar Cells

Abstract

Three benzodipyrrole (BDP)‐based organic small molecules with substituted 4‐methoxyphenyl (CB‐1), 3‐fluorophenyl (CB‐2), and 3‐trifluoromethylphenyl (CB‐3) are designed, synthesized, and used as a hole‐transporting material (HTM) for perovskite solar cells (PSCs). The electrochemical, optical, thermal, electronic, and optoelectronic properties of the HTMs are characterized to verify their suitability for PSCs. The terminal functional groups of the HTMs having different heteroatoms mainly target effective defect passivation of perovskites. Photoluminescence studies and molecular dynamic simulations reveal that fluorine atoms within CB‐2 and CB‐3 can contribute to the defect passivation via interaction with Pb of the perovskite. In particular, a highly planar conformation of CB‐2 on the perovskite surface can facilitate more efficient hole transfer at the interface. Thus, the PSCs employing CB‐2 achieve the highest power conversion efficiency (PCE) of 18.23% while the devices using CB‐1 and CB‐3 exhibit a lower PCE of 16.78% and 16.74%, respectively. PSCs with the BDP‐based HTMs demonstrate excellent long‐term storage stability without degradation in their PCEs over 6 months. The highly planar geometry, defect passivation effect, and hydrophobicity of CB‐2 show its great potential as an HTM for efficient and stable PSCs.

Passivation of Inverted Perovskite Solar Cells by Trifluoromethyl-Group-Modified Triphenylamine Dibenzofulvene Hole Transporting Interfacial Layers

“…Furthermore, the LUMO energy levels were determined by the formula E LUMO = E HOMO + E g. The LUMO energy level values of the HTMs ( CC-1 – 3 ) were −2.28, −2.28, and −2.26 eV, respectively. The calculation results of the LUMO level of the HTM compounds showed higher values than the conduction band of the perovskite, which mean that these will be excellent and effectively block the back-electron transfer …”

“…On the basis of the HI (hysteresis index) calculation, the value of the index was low, under 2%, which could be negligible. 50 Furthermore, the external quantum efficiency (EQE) was determined and is shown in Figure 12c. On the EQE curves, all the cells exhibited great intensity in the range of 350−800 nm.…”

Asymmetrically Substituted 10H,10′H‐9,9′‐Spirobi[acridine] Derivatives as Hole‐Transporting Materials for Perovskite Solar Cells

“…The 3,6-dimethoxy-9H-carbazole units within BSA50 exhibit a near-planar (2D-like) configuration, which may benefit the hole transportation, whereas the bis(4-methoxyphenyl)amine units within BSA51 display a bulkier 3D structure. [21] For the ground state orbitals, both highest occupied molecular orbitals (HOMOs) are concentrated on the borders of the spirobi…”

“…As shown in Figure 2 a‐h, the geometric structures with the ground state orbitals distribution of BSA50 and BSA51 were studied by the Density Functional Theory (DFT). The 3,6‐dimethoxy‐9H‐carbazole units within BSA50 exhibit a near‐planar (2D‐like) configuration, which may benefit the hole transportation, whereas the bis(4‐methoxyphenyl)amine units within BSA51 display a bulkier 3D structure [21] . For the ground state orbitals, both highest occupied molecular orbitals (HOMOs) are concentrated on the borders of the spirobi[acridine] (BSA) core, with BSA50 having a lower HOMO level.…”

Passivating Defects of Perovskite Solar Cells with Functional Donor‐Acceptor–Donor Type Hole Transporting Materials

“…It is known, the introduction of electron-acceptor functional groups in the HTM structure increases the dipole moment, which is beneficial for intramolecular charge transfer (ICT) and increases hole mobility of the resulting HTM. [26][27][28][29] Moreover, the strong interaction in donor-acceptor (D-A) systems effectively suppresses the nonradiative recombination loss and improves the device performance. On the other hand, previous studies have revealed that the uncoordinated Pb 2+ ions at the surface of perovskite are one of the primary sources of defects in the perovskite layer, which could act as charge recombination centers to hinder charge transfer.…”