Deciphering the Reduced Loss in High Fill Factor Inverted Perovskite Solar Cells with Methoxy-Substituted Poly(Triarylamine) as the Hole Selective Contact

Deciphering the Impact of Aromatic Linkers in Self-Assembled Monolayers on the Performance of Monolithic Perovskite/Si Tandem Photovoltaic

Aromatic linker-constructed self-assembled monolayers (Ar-SAMs) with enlarged dipole moment can modulate the work function of indium tin oxide (ITO), thereby improving hole extraction/transport efficiency. However, the specific role of the aromatic linkers between the polycyclic head and the anchoring groups of SAMs in determining the performance of perovskite solar cells (PSCs) remains unclear. In this study, we developed a series of phenothiazine-based Ar-SAMs to investigate how different aromatic linkers could affect molecular stacking, the regulation of substrate work function, and charge carrier dynamics. When served as hole-selective layers (HSLs) in PSCs and monolithic perovskite/silicon tandem solar cells (P/S-TSCs), we found that the Ar-SAM with naphthalene linker along the 2,6-position axis (β-Nap) could form dense and highly ordered HSLs, enhancing interfacial interactions and favoring optimal energy level alignment with the perovskite films. Using this strategy, the optimized wide-band gap PSCs achieved an impressive power conversion efficiency (PCE) of 21.86 % with negligible hysteresis, utilizing a 1.68 eV perovskite. Additionally, the encapsulated devices demonstrated enhanced stability under damp-heat conditions (ISOS-D-2, 50 % RH, 65 °C) with a T91 of 1000 hours. Notably, the fabricated P/S-TSCs, based on solution-processed micron-scale textured silicon heterojunction (SHJ) solar cells, achieved an efficiency of 28.89 % while maintaining outstanding reproducibility. This strategy holds significant promise for developing aromatic linking groups to enhance the hole selectivity of SAMs.

Polymeric Charge-Transporting Materials for Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) hold exceptional promise as next-generation photovoltaic technology, where both perovskite absorbers and charge-transporting materials (CTMs) play critical roles in cell performance. In recent years, polymeric CTMs have played an important role in developing efficient, stable, and large-area inverted PSCs due to their unique properties of high conductivity, tunable structures, and mechanical flexibility. This review provides a comprehensive overview of polymeric CTMs used in inverted PSCs, encompassing polymeric hole transport materials (HTMs) and electron transport materials (ETMs). the relationship between their molecular structures, modification strategies are systematically summarized and analyzed for adjusting energy levels, and improving charge extraction, enabling a deep understanding of these widely used materials. The review also explores effective strategies for designing even more efficient polymeric CTMs. Finally, an outlook is proposed on the exciting research of novel polymeric CTMs, paving the way for their commercialized applications in PSCs.

Controlled NiOx Defect Engineering to Harnessing Redox Reactions in Perovskite Photovoltaic Cells via Atomic Layer Deposition

Albeit the undesirable attributes of NiOx, such as low conductivity, unmanageable defects, and redox reactions occurring at the perovskite/NiOx interface, which impede the progress in inverted perovskite solar cells (i-PSCs), it is the most favorable choice of technology for industrialization of PSCs. In this study, we propose a novel Ni vacancy defect modulate approach to leverage the conformal growth and surface self-limiting reaction characteristics of the atomic layer deposition (ALD)-fabricated NiOx by varying the O2 plasma injection time (tOE) to induce self-doping. Consequently, NiOx thin films with enhanced conductivity, an appropriate Ni3+/Ni2+ ratio, stable surface states, and ultrathinness are realized as hole-transporting layers (HTLs) in p-i-n PSCs. As a result of these improvements, ALD-NiOx-based devices exhibit the highest power conversion efficiency (PCE) of 19.86% and a fill factor (FF) of 81.86%. Notably, the optimal interfacial defects effectively suppressed the severe reaction between the perovskite and NiOx. This suppression is evidenced by the lowest decay rate observed in a harsh environment, lasting for 500 consecutive hours. The proposed approach introduces the possibility of a hierarchical distribution of defects and offers feasibility for the fabrication of large-area, uniform, and high-quality films.

Highly Solvent Resistant Small-Molecule Hole-Transporting Materials for Efficient Perovskite Quantum Dot Light-Emitting Diodes

Perovskite quantum dot light-emitting diodes (Pe-QLEDs) have been shown as promising candidates for next-generation displays and lightings due to their unique feature of wide color gamut and high color saturation. Hole-transporting materials (HTMs) play crucial roles in the device performance and stability of Pe-QLEDs. However, small-molecule HTMs have been less studied in Pe-QLEDs due to their poor solvent resistance and low hole mobility. In this work, three novel small-molecule HTMs employing benzimidazole as the center core, named X4, X5, and X6, were designed and synthesized for application in Pe-QLEDs. One of the tailored HTM-X6 exhibits excellent solvent resistant ability to the perovskite quantum dot (QD) inks due to its proper solubility and low surface energy. Our result clearly demonstrated that the synergistic effect of poor solubility and low surface energy facilitates the achievement of good solvent resistance to perovskite QD inks. As a result, a promising maximal external quantum efficiency (EQE) of 14.1% is achieved in X6-based CsPbBr3 Pe-QLEDs, which is much higher than that of X4 (9.16%) and X5 (6.60%)-based devices, which is comparable to the PTAA reference (EQE ∼ 15.8%) under the same conditions. To the best of our knowledge, this is the first example that a benzimidazole-based small-molecule HTM demonstrated a good application in Pe-QLEDs. Our work provides new guidance for the rational design of small-molecule HTMs with high solvent resistance for efficient Pe-QLEDs and other photoelectronic devices.

A Multifunctional Fluorinated Polymer Enabling Efficient MAPbI3-Based Inverted Perovskite Solar Cells

Exploring polymeric hole-transporting materials (HTMs) with passivation functions represents a simplified and effective approach to minimize the perovskite defect density. To date, most of reported polymeric HTMs were applied to fabricate n-i-p regular perovskite solar cells (PSCs). The polymers compatible for p-i-n inverted PSCs were very limited. Moreover, the passivation polymers were devoted to passivate the uncoordinated Pb²⁺. However, the MA⁺ cation defect has profound unwanted effect on device efficiency and long-term stability. In order to synchronously passivate the Pb²⁺ and MA⁺ defects in p-i-n inverted PSCs, a new nonfused polymer was intentionally explored via mild polymerization. The aromatic bridge instead of long alkyl chains enabled polymer BN-12 to achieve excellent thermal stability and good wettability of perovskite precursor. Furthermore, the incorporation of chemical anchor sites ("C═O" and "F") strongly controlled the crystallization of perovskite and restrained the MA⁺ ion migration. As a result, a significant fill factor (FF) of 82.9% and an enhanced power conversion efficiency (PCE) of 20.28% were achieved for MAPbI₃-based devices with the dopant-free BN-12, exceeding those with the commercial HTM PTAA (FF = 81.7%, PCE = 19.51%). More importantly, the unencapsulated devices based on BN-12 realized outstanding long-term stability, maintaining approximately 95% of its initial efficiency after stored for 85 days. By contrast, the PTAA-based device showed rapid decrease which retained only 50% of its initial value after 45 days.