Prashant Sonar1 Hong Duc Pham3 Sagar Jain5 Yeng Ming Lam4 Yabing Qi2

1, Queensland University of Technology, Brisbane, Queensland, Australia
3, Queensland University of Technology, Brisbane, Queensland, Australia
5, Swansea University Bay Campus, Swansea, , United Kingdom
4, Nanyang Technology University, Singapore, , Singapore
2, Okinawa Institute of Science and Technology Graduate School (OIST), Okinawa, , Japan

Perovskite solar cells (PSCs) technology has attracted a big attention in the solar cell community due to their exceptional performance as the power conversion efficiency (PCE) surged to world record 22%. Though the highest PCE of 22.1% up to date used PTAA as polymeric hole transporting material (HTM) but it has some disadvantages such as super high cost and reproducibility. In contrast to polymers, small molecules possess advantages, e.g. batch-to-batch reproducibility, easy purification, high purity & definite structure. Among small molecular HTMs for PSCs, Spiro-OMeTAD has been employed intensively as standard HTM. Despite of the remarkable performance (20.8%), some main drawbacks of Spiro-OMeTAD, including high cost and multistep synthesis, can hamper the progress of low cost and large area flexible PSCs.1, 2

Herein, six new simple cost efficient solution processable small molecular HTMs, namely TPA-BPV-TPA, TPA-BP-TPA, TPA-TVT-TPA, TPA-NAP-TPA, TPA-ANT-TPA, and ACE-ANT-ACE, using triphenylamine(TPA) and acenaphthylene(ACE) as end-capping groups with different cores are reported. The variation in cores is aimed to change the highest occupied molecular orbital (HOMO) energy level of each HTM to match ot with the HOMO level of perovskite, enhancing the hole extraction and efficient performance.3-6 Thereafter, TPA-ANT-TPA, ACE-ANT-ACE, TPA-BPV-TPA and TPA-BP-TPA were implemented in mesoporous perovskite devices whereas TPA-TVT-TPA and TPA-NAP-TPA were fabricated in inverted ones. In case of conventional layouts, while doped TPA-BPV-TPA based devices give efficiency around 16.42%, dopant-free TPA-ANT-TPA ones achieves an overall efficiency of 17.5%. Notably, both TPA-BPV-TPA and TPA-ANT-TPA exhibits an impressive stability compared to Spiro-OMeTAD under identical aging condition. Additionally, TPA-ANT-TPA possesses the low synthetic cost of $67/g compared to that of Spiro-OMeTAD ($91/g). For inverted architecture, the devices based on pristine TPA-TVT-TPA and TPA-NAP-TPA as HTMs are found to be of 16.32% and 14.63%, respectively. The cut-price and straightforward synthesis with elegant scale up makes these classes of materials important for the industry to produce high-throughput printed perovskite solar cells for large area applications.

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[2] N. J. Jeon, J. H. Noh, W. S. Yang, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok, Nature 2015, 517, 476
[3] H. D. Pham, Z. Wu, L. K. Ono, S. Manzhos, K. Feron, N. Motta, Y. Qi, P. Sonar, Adv. Electron. Mater. 2017, 3, 1700139
[4] H. D. Pham, H. Hu, K. Feron, S. Manzhos, H. Wang, Y. M. Lam, P. Sonar, Solar RRL. 2017, 1, 1700105
[5] Patent filed
[6] H. D. Pham, T. T, Do, J. Kim, C. Charbonneau, S. Manzhos, K. Feron, W. C. Tsoi, J. Durrant, S. M. Jain, P. Sonar, manuscript submitted to Adv. Ener. Mater.