| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 107 === In chapter 3, three azahelicene derivatives with electron-rich bis(4-methoxyphenyl)-amino or bis(p-methoxyphenyl)aminophenyl groups at the terminals were deliberately designed, synthesized, and characterized as HTMs for PSCs. A maximum PCE of 17.34% was observed for the bis(p-methoxyphenyl)amino-substituted derivative (SY1) and 16.10% for the bis(p-methoxyphenyl)aminophenyl-substituted derivative (SY2). Longer-chain substituent such as hexyloxy group (SY3) greatly diminishes the efficiency. In addition, the dopant-free devices fabricated with SY1 as the HTM shows an average PCE of 12.13%, which is significantly higher than that of spiro-OMeTAD (7.61%). The ambient long-term stability test revealed that after 500 h, the devices prepared from SY1 and SY2 retained more than 96% of its initial performance, which is much improved than the reference device with standard spiro-OMeTAD as the HTM under the same conditions. Detailed material cost analysis reveals that the material cost for SY1 is less than 8% of that for spiro-OMeTAD.
In view of the many advantages of the helicene structure, in chapter 4, another two inexpensive and efficient HTMs based on a carbohelicene core, CH1 and CH2, were developed to realize efficient and stable conventional PSCs. Owing to the rigid conformation of helicene-core, both compounds possess unique and strong CH− interactions in the polycrystalline packing pattern and good phase stabililty, which are distinct from the π−π intermolecular interactions of conventional planar and spiro-type molecules. Surprisingly, CH1 and CH2 derived PSCs delivered an impressive efficiency of > 19% and 18.71%, respectively, outperforming the (18.45%) of control device based on spiro-OMeTAD. Furthermore, both PSCs also possess better ambient stability, for which 90% of initial performance is retained after aging in a dry box with a 30% relative humidity at 28-32°C for over 500 h. Considering the low product cost of both compounds (< 1/10 of that for spiro-OMeTAD), these newly designed carbohelicene-type HTMs are promising potential candidates for the commercialization of PSCs.
Finally, we found that phenanthrene (Phe) combined the advantages of both low-cost and electron-rich aromatic unit, which can be easily obtained by two steps in mild conditions. Herein, we synthesized two low-cost U-shaped HTMs, U1 and U2. From crystal structure, both compounds possess strong CH− interactions in the polycrystalline packing pattern and U1 also has hydrogen bonding force. Surprisingly, U1 and U2 enable their derived PSCs to deliver high efficiency of 18.71 and 17.11%, respectively. Furthermore, both PSCs also possess better ambient stability, for which 85% of initial performance is retained after aging in a dry box for over 500 h.
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