In recent few years, the efficiency of organic-inorganic metal halide perovskite-based solar cells (PSCs) has been improved rapidly, because of the significant efforts in materials development and device fabrications. Hole transporting materials (HTMs) play an important role to the PSCs in charge extraction and interface modification. Currently, the most extensively studied and applied HTM for perovskite devices is 2,2’,7,7’-tetrakis(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene (Spiro-OMeTAD),[2-4] which is expensive because of its relative long synthesis and purification processes. For achieving large area solar cells, devices with satisfactory efficiencies and low-cost materials are urgently required. Thus, the development of high efficient and low-cost HTMs is very necessary for promoting PSCs from lab scale experimentation towards industrial scale application.
We have been working on the development of new organic and polymeric HTMs. For example, two HTMs were synthesized by connecting the arylamine side groups to the both sides of thiophene and/or benzene moieties, named as HTM1 and HTM2, respectively, in which the synthesis procedures are much shorter and simpler than those of Spiro-OMeTAD. When applied in the PSCs devices, the thiophene-based HTM1 and benzene-based HTM2 showed short circuit photocurrent densities (Jscs) of 21.08 mA cm-2 and 15.83 mA cm-2 , open circuit voltages (Vocs) of 1.01 V and 0.79 V and fill factors (FFs) of 0.59 and 0.46 respectively. The devices with the two HTMs showed average power conversion efficiencies (PCEs) of 13.7% and 6.4 % with best PCEs of 14.7% and 7.5%, while the device with Spiro-OMeTAD has a best PCE of 15.8% under the similar device preparation method and measurement conditions. These observations indicated that thiophene-based HTM1 has a comparable performance to the Spiro-OMeTAD. These results showed that selecting a proper π-linker is important for the performance of the HTMs. And the simple material of HTM1 is a promising HTM with the potential to replace the expensive Spiro-OMeTAD due to its comparable performance with much simpler synthesis route and much reduced cost (less than 1/10 folds of that of Spiro-OMeTAD).
1. Calió, L.; Kazim, S.; Grätzel, M.; Ahmad, S., Angew. Chem. Int. Ed. 2016, 55, 14522-14545.
2. Ding, I. K.; Tétreault, N.; Brillet, J.; Hardin, B. E.; Smith, E. H.; Rosenthal, S. J.; Sauvage, F.; Grätzel, M.; McGehee, M. D., Adv. Funct. Mater. 2009, 19, 2431-2436.
3. Jeon, N. J.; Lee, H. G.; Kim, Y. C.; Seo, J.; Noh, J. H.; Lee, J.; Seok, S. I., J. Am. Chem. Soc. 2014, 136, 7837-40.
4. Liu, D.; Kelly, T. L., Nat. Photon. 2014, 8, 133-138.