A series of hole-transporting materials (HTMs) based on [2,2]paracyclophane and triphenyl-amine (TPA) was synthesized. We studied the effect of the chemical structure of the HTM on the photovoltaic performance of perovskite solar cells by varying the number of TPA charge transporting components in the HTM. Tetra-TPA, in which four TPAs are incorporated into the [2,2]paracyclophane core, exhibited better hole transport properties than di-TPA and tri-TPA, which contain two and three TPAs, respectively. In particular, incorporation of the TPA group with a multi-armed structure effectively enhanced the conductivity of the HTM layer in the out-of-plane direction in the solar cell device. Due to the improved charge transport and appropriate molecular energy levels of tetra-TPA, the perovskite solar cell based on the tetra-TPA HTM achieved higher Jsc and FF values than the devices based on di-TPA and tri-TPA HTMs, with a high solar cell efficiency (17.9%).
Bibliographical noteFunding Information:
This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System and Basic Science Research Program (2015R1A1A1A05001115) funded by the National Research Foundation under the Ministry of Science, Korea Institute of Science and Technology (KIST, 2E26520), and Nano Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Grant 2012M3A7B4049989). K. K. thanks the NRF for its support (no. 2013R1A1A1010130). The authors thank Dongkyun Seo in Department of Chemistry at Chung-Ang University for assistance with the DFT calculations.
© 2016 The Royal Society of Chemistry.
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