Effects of Self‐Assembled Monolayer Modification of Nickel Oxide Nanoparticles Layer on the Performance and Application of Inverted Perovskite Solar Cells

Abstract

Entirely low‐temperature solution‐processed (≤100 °C) planar p‐i‐n perovskite solar cells (PSCs) offer great potential for commercialization of roll‐to‐roll fabricated photovoltaic devices. However, the stable inorganic hole‐transporting layer (HTL) in PSCs is usually processed at high temperature (200–500 °C), which is far beyond the tolerant temperature (≤150 °C) of roll‐to‐roll fabrication. In this context, inorganic NiOx nanoparticles (NPs) are an excellent candidate to serve as the HTL in PSCs, owing to their excellent solution processability at room temperature. However, the low‐temperature processing condition is usually accompanied with defect formation, which deteriorates the film quality and device efficiency to a large extent. To suppress this setback, we used a series of benzoic acid selfassembled monolayers (SAMs) to passivate the surface defects of the NiOx NPs and found that 4‐bromobenzoic acid could effectively play the role of the surface passivation. This SAM layer reduces the trap‐assisted recombination, minimizes the energy offset between the NiOx NPs and perovskite, and changes the HTL surface wettability, thus enhancing the perovskite crystallization, resulting in more stable PSCs with enhanced power conversion efficiency (PCE) of 18.4 %, exceeding the control device PCE (15.5 %). Also, we incorporated the above‐mentioned SAMs into flexible PSCs (F‐PSCs) and achieved one of the highest PCE of 16.2 % on a polyethylene terephthalate (PET) substrate with a remarkable power‐per‐weight of 26.9 W g−1. This facile interfacial engineering method offers great potential for the large‐scale manufacturing and commercialization of PSCs.

Ligand‐Free, Highly Dispersed NiOx Nanocrystal for Efficient, Stable, Low‐Temperature Processable Perovskite Solar Cells

“…Jaramillo et al have elucidated the mechanism underlying the stabilization of solution‐processed W‐NiO x nanoparticles and have used that knowledge to produce a rigid PSC with a PCE of 16.6% and null hysteresis . Recently, Jen et al developed a benzoic acid‐derivative self‐assembled monolayer interfacial modification method that was used to produce rigid and flexible, W‐NiO x ‐based, inverted PSCs with a PCE of 18.4 and 16.2%, respectively . Unfortunately, the stability of PSCs made by using low‐temperature W‐NiO x remains inferior to that of devices fabricated with high‐temperature‐processed charge‐transporting layers .…”

“…[32] Unfortunately, the stability of PSCs made by using low-temperature W-NiO x remains inferior to that of devices fabricated with high-temperature-processed chargetransporting layers. [23,32] One reason for this is that the W-NiO x surface tends to adsorb ligands (e.g., water molecules, residual nitrate, hydroxide, and sodium ions) during the preparation process, [31] which reduces the stability of the devices. These ligands are difficult to remove from low-temperature processes.…”

Analysing the Prospects of Perovskite Solar Cells within the Purview of Recent Scientific Advancements

“…PTPD is a hydrophobic HTL, so it restricts moisture interaction with perovskite film. Wang and his co-workers showed an inorganic NiO x nanoparticles based HTL with para-bromobenzoic acid showing good stability, while maintaining 80% of its initial PCE after 15 days of exposure to 30% humidity [179]. This is accounted for the enhanced film morphology and passivation of defect states in NiO x by para-bromobenzoic acid.…”

Recent Progress of Flexible Perovskite Solar Cells

“…To further improve the quality of NiO x HTL, 4‐bromobenzoic acid self‐assembled monolayer was deposited onto the top of the NiO x film, which passivated the NiO x surface, improved the wettability and enhanced the perovskite crystallization, leading to the highest PCE of 16.2% for the resulting FPSC on a PET substrate . Cu(NO 3 ) 2 was also introduced to the reaction solution of Ni(OH) 2 to prepare Cu‐doped NiO x NPs, which was proved to increase the conductivity of the NiO x film .…”