Date Published: January 31, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Šarūnė Daškevičiū tė, Nobuya Sakai, Marius Franckevičius, Marytė Daškevičienė, Artiom Magomedov, Vygintas Jankauskas, Henry J. Snaith, Vytautas Getautis.
Novel nonspiro, fluorene‐based, small‐molecule hole transporting materials (HTMs) V1050 and V1061 are designed and synthesized using a facile three‐step synthetic route. The synthesized compounds exhibit amorphous nature with a high glass transition temperature, a good solubility, and decent thermal stability. The planar perovskite solar cells (PSCs) employing V1050 generated an excellent power conversion efficiency of 18.3%, which is comparable to 18.9% obtained with the state‐of‐the‐art Spiro‐OMeTAD. Importantly, the devices based on V1050 and V1061 show better stability compared to devices based on Spiro‐OMeTAD when aged without any encapsulation under uncontrolled humidity conditions (relative humidity around 60%) in the dark and under continuous full sun illumination.
Due to the merits of intense absorption in an almost entire visible spectral region, perovskite materials first emerged as dye substitutes for dye‐sensitized solar cells with the liquid electrolyte showing a power conversion efficiency (PCE) around 4%.1 Since the first perovskite‐based solar cells (PSCs) suffered from fast degradation their architecture was shifted from liquid electrolyte‐based low PCE devices to solid‐state devices using small organic hole transporting molecule 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxy‐phenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD).2 In consequence, the photovoltaic performances have skyrocketed to 21.1% for small‐area cells3 and 20.5% for cells4 with the active area larger than 1 cm2 in just a few years. Since then, Spiro‐OMeTAD became a standard material for the development of the new hole transporting materials (HTMs) for PSCs. In the majority of the state‐of‐the‐art devices, Spiro‐OMeTAD is used as a hole transporting material.5, 6, 7, 8 However, the tedious synthetic procedures and purification processes of this HTM make it cost ineffective and thus limit its application and commercialization.9 Moreover, the study by A. Binek et al. showed that Spiro‐OMeTAD can significantly contribute to the overall cost of materials required for the PSC manufacturing.10
In conclusion, a new promising nonspiro fluorene‐based hole transport materials V1050 and V1061 were synthesized and characterized. The synthesis of these HTMs consists of three steps starting from the commercially available materials. Solar cells using V1050 exhibit PCEs of 18.3% which is comparable to the performance of PSC comprising Spiro‐OMeTAD (18.9%) as HTM. Compared with Spiro‐OMeTAD, new HTM additionally shows several significant advantages: it has much facile synthesis, has high glass transition temperature (166 °C) and does not form the crystalline state. Moreover, this new HTM also exhibits better environmental stability compared to Spiro‐OMeTAD. We believe that the V1050 can be a useful alternative HTM to Spiro‐OMeTAD for perovskite solar cells, thus bringing PSCs closer to commercial production.
The authors declare no conflict of interest.