After perovskite materials are used in solid-state batteries, the battery efficiency increases rapidly and has exceeded 25%. Jeon et al. obtained a mesoporous perovskite battery with an efficiency of 16.7% by adjusting the methoxy group sites on Spiro-OMeTAD . Since the purification of Spiro-OMeTAD is troublesome, many hole transport materials containing triphenylamine like spiro-OMeTAD are synthesized (Figure 1). The CH3NH3PbI3 battery using triphenylamine polymer PTAA also achieved an efficiency of 16.2%. However, these triphenylamine-based transport materials are superior to their conjugated parts and are not coplanarly spaced, and they cannot form an ordered stack through spin coating. Therefore, their own charge transport properties are very weak, and they need to be added by adding Li- TFSI and tBP can improve hole transport and achieve better device effects.
In addition, there are also reports of using high molecular conjugated polymers as hole transport layers in perovskite batteries (Figure 2). When P3HT is used as a hole transport layer in planar structure perovskite cells, the cell efficiency reaches more than 10%. Other researchers used PDPPDBTE as a hole transport layer and achieved an efficiency of 9.2% in a perovskite cell with a porous structure, surpassing the traditional hole transport material Spiro-OMeTAD. These conjugated polymers, originally used as donors in thin-film solar cells, have excellent intrinsic transport properties. However, in literature reports, higher devices still use Li-TFSI and tBP as additives.
However, Li-TFSI is easy to absorb moisture and will also liquefy at higher humidity. Its existence will not only increase the production cost, but also damage the lower perovskite layer that is very sensitive to water, which is detrimental to the stability of the device. Therefore, it is necessary to optimize and improve the above-mentioned hole transport system. We should not only consider the performance of the device, but more importantly, its impact on the stability of the device. To obtain better humidity stability, the use of this type of hydrophilic ionic additives should be avoided. This places high requirements on hole transport materials: first, it must have good hole mobility itself; thus eliminating the need for doped hydrophilic ion additives; second, it must have good hole mobility Only by its hydrophobicity can it be able to function as a water vapor barrier; third, it must be fabricated by solution method, so as to meet the needs of practical applications; fourth, its other physical properties must match those of perovskite. Suitable for use in perovskite cells. Currently, only a few hole transport materials can achieve comparable efficiencies to spiro-OMeTAD without adding such ionic additives. Gratzel et al. reported a branched conjugated hole transport material Fused-F. It achieves 12.8% efficiency without adding additives. However, its synthesis steps are very complicated and it does not show any advantages in stability.
Latest research progress in perovskite solar cells
1. Team of Ma Zhu & Lin Yuanhua of Southwest Petroleum University & Sun Kuan of Chongqing University: Anti-aging precursor with ultra-wide annealing window for 24.08% perovskite solar cells
https://onlinelibrary.wiley.com/doi/10.1002/aenm.202302769
2. Fudan University Zhang Hong & EPFL Michael Grätzel team: Implementing high-efficiency HTM-free perovskite solar cells through interface modulation of mixed-dimensional heterostructures
https://onlinelibrary.wiley.com/doi/10.1002/adfm.202309789
3. SUSTech Qiu Longbin’s research group "Small": Humidity promotes the diffusion of organic amine salts to prepare high-quality vapor-deposited perovskite films
https://onlinelibrary.wiley.com/doi/10.1002/smll.202307960
4. Viktor V. Brus team of Nazarbayev University: Effect of short pulse high-intensity proton irradiation on high-performance perovskite solar cells
https://onlinelibrary.wiley.com/doi/10.1002/adfm.202310404
5. Beijing University of Chemical Technology Li Minghua & Tan Zhan'ao's latest EES: Synergistic electrical management and light management can achieve high-efficiency monolithic inorganic perovskite/organic tandem tandem solar cells with an efficiency exceeding 24%
https://pubs.rsc.org/en/Content/ArticleLanding/2023/EE/D3EE02940A
6. Chen Zhaolai from Shandong University’s latest Matter: Phase-stable FAPbl3-based single crystal has an electron diffusion length of 600 μm https://www.sciencedirect.com/science/article/abs/pii/S2590238523005222
7. Wuhan University’s Fang Guoguo, Ke Weijun, Weiwei Meng and others exceeded 22% efficiency! High-efficiency wide-bandgap perovskite cells!
https://onlinelibrary.wiley.com/doi/10.1002/adma.202307987
8. In-situ decomposition of organometallic chalcogenides and directional perovskite defect management by the team of Xu Gang from the Fujian Institute of Material Structure, Chinese Academy of Sciences and Cao Jing from Lanzhou University