Novel Low Cost Triphenylamine Derivatives based Hole Transporting Organic Materials for Highly Efficient and Stable Perovskite Solar Cells

Hong Duc Pham^a, Hongwei Hu^b, Zhifang Wu^c, Thu Trang Do^a, Luis K. Ono^c, Krishna Feron^d, Sergei Manzhos^e, Hongxia Wang^a, Nunzio Motta^a, Yeng Ming Lam^b, Yabing Qi^c, Sagar Motilal Jain^f, Prashant Sonar^a

^aSchool of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), Australia, George Street, 2, Brisbane City, Australia

^bNTU Singapore - Nanyang Technological University, School of Materials Science and Engineering, Nanyang Avenue, 50, Singapore, Singapore

^cEnergy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa, Japan

^dCentre for Organic Electronics, University of Newcastle, University Drive, Callaghan, NSW 2308

^eDepartment of Mechanical Engineering, Faculty of Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, Singapore 117576

^fSPECIFIC, College of Engineering Swansea University, SPECIFIC, Baglan Bay Innovation Centre, Central Avenue, Baglan, Port Talbot, SA12 7AX, United Kingdom

Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics 2018 (AP-HOPV18)

Kitakyūshū-shi, Japan, 2018 January 28th - 30th

Organizers: Shuzi Hayase, Juan Bisquert and Hiroshi Segawa

Poster, Hong Duc Pham, 079
Publication date: 27th October 2017

Currently, 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 the world record 22% within last seven years. Though the highest PCE of 22.1% up to date used poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) as the hole transporting material (HTM), polymeric HTMs have some disadvantages related to the reproducibility of their synthesis and purification. In contrast to polymers, small molecules possess various advantages, including better batch-to-batch reproducibility, ease of purification, high purity, and definite structure. Among small molecular HTMs for PSCs, 2,2’,7,7’-tetrakis(N,N’-di-pmethoxyphenylamino)-9,9’-spirbiuorene (Spiro-OMeTAD) has been employed intensively as standard HTM. Despite 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.

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 p-conjugated cores, including biphenylene-vinylene(BPV), biphenylene(BP), thiophene-vinylene-thiophene(TVT), and naphthalene(NAP), and anthanthrone(ANT) are reported. The variation of these cores is aimed to change the highest occupied molecular orbital (HOMO) energy level of each HTM to match the proper energy level alignment with the HOMO level of perovskite (CH₃NH₃PbI₃), enhancing the hole extraction and efficient performance. 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. For conventional layouts, while doped TPA-BPV-TPA based devices give efficiency around 16.42%, dopant-free TPA-ANT-TPA ones achieve an overall efficiency of 17.5%. Notably, both TPA-BPV-TPA and TPA-ANT-TPA exhibit 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 architectures, 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. Particularly, TPA-TVT-TPA exhibits an impressive V_oc of 1.07 V, being one of the highest performances in inverted PSCs. Our study illustrates that our novel compounds, TPA-ANT-TPA, TPA-BPV-TPA, and TPA-TVT-TPA, are taken into account as the promising candidate HTMs of conventional and inverted PSCs, especially HTMs based on the cost-efficient anthanthrone dye. The cut-price and straightforward synthesis with elegant scale up makes these classes of materials important for large area applications of printed perovskite solar cells.

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