Evaporated Self‐Assembled Monolayer Hole Transport Layers: Lossless Interfaces in p‐i‐n Perovskite Solar Cells

Abstract

Engineering of the interface between perovskite absorber thin films and charge transport layers has fueled the development of perovskite solar cells (PSCs) over the past decade. For p‐i‐n PSCs, the development and adoption of hole transport layers utilizing self‐assembled monolayers (SAM‐HTLs) based on carbazole functional groups with phosphonic acid anchoring groups has enabled almost lossless contacts, minimizing interfacial recombination to advance power conversion efficiency in single‐junction and tandem solar cells. However, so far these materials have been deposited exclusively via solution‐based methods. Here, for the first time, vacuum‐based evaporation of the most common carbazole‐based SAM‐HTLs (2PACz, MeO‐2PACz, and Me‐4PACz) is reported. X‐ray photoelectron spectroscopy and infrared spectroscopy demonstrate no observable chemical differences in the evaporated SAMs compared to solution‐processed counterparts. Consequently, the near lossless interfacial properties are either preserved or even slightly improved as demonstrated via photoluminescence measurements and an enhancement in open‐circuit voltage. Strikingly, applying evaporated SAM‐HTLs to complete PSCs demonstrates comparable performance to their solution‐processed counterparts. Furthermore, vacuum deposition is found to improve perovskite wetting and fabrication yield on previously non‐ideal materials (namely Me‐4PACz) and to display conformal and high‐quality coating of micrometer‐sized textured surfaces, improving the versatility of these materials without sacrificing their beneficial properties.

Fabrication of Highly Luminescent Quasi Two-Dimensional CsPbBr3 Perovskite Films in High Humidity Air for Light-Emitting Diodes

“…As Figure a presents, these SAMs are characterized by a phosphonic acid head and carbazole group, which shows an outstanding hole transporting property. − It has been reported that the phosphonic acid head in the SAMs is inclined to bind to the substrate, with the hydrophobic carbazole group facing upward to contact with the perovskite layer (Figure b) . Such arrangement of SAMs leads to a hydrophobic surface, which is confirmed by the contact angle measurement.…”

“…To obtain high-quality and bright perovskite films for constructing LEDs, suitable HTL materials need to be used. Self-assembled monolayer (SAM) materials have emerged as promising HTL materials for constructing high-performance perovskite optoelectronic devices in recent years. − Here, we select two representative SAM materials as HTLs for depositing perovskite films in ambient air, i.e., 2PACz and MeO-2PACz.…”

Advantages and challenges of self-assembled monolayer as a hole-selective contact for perovskite solar cells

“…Possible inhomogeneities such as unabsorbed SAM molecules can be removed by post-treatment, such as solvent washing. Recently, an interesting work reported that SAMs can be fabricated by vapor-phase deposition [60], which is also promising for future large-scale manufacturing.…”

Understanding and Mitigating the Degradation of Perovskite Solar Cells Based on a Nickel Oxide Hole Transport Material during Damp Heat Testing

“…Focusing on hole transport materials, high efficiencies have been obtained with extremely thin organic HTMs such as poly­(4-butyltriphenylamine) (poly-TPD), − poly­[ bis (4-phenyl)­(2,4,6-trimethylphenyl)­amine] (PTAA), and carbazole-based self-assembling monolayers (SAMs). − For small areas (<1 cm 2 ), these devices often outperform those with inorganic HTM in terms of efficiency . However, the deposition of <5 nm thick organic layers over a large scale by solution processes, such as spin coating, dip coating, and slot-die coating, is challenging and prone to pinhole formation, especially in the case of textured surfaces such as those used by the Si PV industry.…”