Key Takeaways & Executive Findings
- •• • The NiOx/1,5-NOT-based device achieves a power conversion efficiency (PCE) of 24.20%, surpassing the NiOx control (18.12%) and 2,6-NOT-based (21.87%) devices, demonstrating a relative improvement of 33.5% over the control. • • The molecular planarity modulation via 1,5-NOT enhances hole extraction and transport capabilities and increases the conductivity of NiOx, directly addressing the bottleneck of low intrinsic conductivity in NiOx. • • The 1,5-NOT modification leads to excellent long-term stability, attributed to reduced interfacial defects and suppressed charge recombination, which is critical for commercial viability. • • The study provides a new strategy for NiOx modification using small organic molecules, with the planarity of the modifier being a key design parameter for optimizing hole transport in inverted PSCs.
Abstract
Nickel oxide (NiOx) is widely used as a hole transport material in inverted perovskite solar cells (PSCs). However, its practical application is limited by low intrinsic conductivity and insufficient hole extraction ability, leading to significant interfacial defects that reduce device efficiency and stability. To overcome these issues, two isomeric small organic molecules, 2,6-NOT and 1,5-NOT, were developed and introduced to modify NiOx. These isomers share the same structure but differ in the substitution positions of functional groups, resulting in distinct molecular planarity. Experimental results demonstrate that 1,5-NOT, featuring extended conjugation and enhanced planarity, more effectively enhances the hole extraction/transport capabilities and conductivity of NiOx compared to 2,6-NOT. The NiOx/1,5-NOT-based device achieves a remarkable power conversion efficiency (PCE) of 24.20%, along with excellent long-term stability, surpassing the NiOx control device (18.12%) and the 2,6-NOT-based device (21.87%). These findings indicate that modifying NiOx with small organic molecules significantly improves charge transport performance, and increasing molecular planarity is particularly beneficial for enhancing hole transport and reducing defect density, thereby increasing both efficiency and stability. This work provides a new strategy for NiOx modification via small organic molecules, offering a promising route to high-performance inverted PSCs.
1. Introduction
Inverted perovskite solar cells (PSCs) have emerged as a leading photovoltaic technology due to their simplified fabrication, low-temperature processing, and enhanced stability. However, the hole transport material (HTM) at the perovskite interface critically influences device performance. Nickel oxide (NiOx) is a promising HTM owing to its facile synthesis, high transparency, and chemical stability, yet its intrinsically low conductivity and insufficient hole extraction capability limit device efficiency. Furthermore, the presence of high-oxidation-state nickel species (Ni>3+) can induce detrimental reactions with the perovskite, accelerating degradation. These challenges necessitate interface engineering to optimize energy alignment, passivate defects, and suppress recombination.
This study introduces two isomeric small organic molecules, 2,6-NOT and 1,5-NOT, as interfacial modifiers for NiOx. By varying the substitution position, the molecular planarity is modulated, with 1,5-NOT exhibiting extended conjugation and enhanced planarity. This structural variation directly impacts the hole transport properties of the modified NiOx layer. The experimental results demonstrate that 1,5-NOT significantly improves hole extraction and conductivity, leading to a remarkable PCE of 24.20% and excellent stability. This work highlights the importance of molecular planarity in designing effective interfacial modifiers and provides a new strategy for enhancing NiOx-based inverted PSCs.
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Miaoxin Li, Hao Sun, Fei Wu, Huilin Xie, Mingxin Wang, Junhong Tan, Cheng Zhong, Linna Zhu (2026). Enhancing NiOx Hole Transport Properties through Planarity Modulation of Organic Small Molecules for Inverted Perovskite Solar Cells. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3605-0
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Frequently Asked Questions
What is the specific role of molecular planarity in enhancing the hole transport properties of NiOx?
The study demonstrates that 1,5-NOT, with its extended conjugation and enhanced planarity, more effectively enhances hole extraction and transport capabilities compared to 2,6-NOT. This is attributed to improved molecular packing and electronic coupling, which increases the conductivity of NiOx and reduces interfacial defects, leading to a higher PCE of 24.20% versus 21.87% for 2,6-NOT.
How does the modification with 1,5-NOT affect the long-term stability of the perovskite solar cells?
The NiOx/1,5-NOT-based device exhibits excellent long-term stability, surpassing both the control and 2,6-NOT-based devices. This is due to the passivation of interfacial defects and suppression of charge recombination, which mitigates the degradation pathways associated with NiOx, such as reactions with perovskite components.
What are the key performance metrics of the NiOx/1,5-NOT device compared to the control?
The NiOx/1,5-NOT device achieves a PCE of 24.20%, significantly higher than the NiOx control (18.12%) and the 2,6-NOT-based device (21.87%). This represents a relative improvement of 33.5% over the control, demonstrating the effectiveness of the molecular modification.
What is the industrial relevance of this work for large-scale production of inverted PSCs?
The use of small organic molecules as interfacial modifiers offers a simple and scalable approach to enhance NiOx performance. The improved efficiency and stability are critical for commercial viability, and the molecular design principles (planarity modulation) can be extended to other HTMs, potentially accelerating the deployment of inverted PSCs.
Are there any potential drawbacks or limitations of using 1,5-NOT as an interfacial modifier?
While the study reports significant improvements, potential limitations include the additional processing step and the cost of the organic molecules. However, the substantial gains in efficiency and stability justify the added complexity, and further optimization could reduce costs.
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