Simple 9,10-dihydrophenanthrene based hole-transporting materials for efficient perovskite solar cells

It is a very important task of searching for novel hole-transporting materials (HTMs), along with effective building blocks, on the way towards commercialization of the perovskite solar cells (PSCs). 9,10-Dihydrophenanthrene (DHP) is a rigid conjugated system, whose skeleton is closely analogous to the widely used fluorene unit in developing HTMs. Herein, for the first time, DHP employed as a promising building block in the construction of HTMs for PSCs is presented. Two readily-available DHP-cored small molecules, namely K-DHP-1 and K-DHP-2, were synthesized and characterized. An attractive bridged ketal pattern of the two molecules was revealed by the X-ray crystallography of K-DHP-2. Afterwards, the two compounds were applied as HTMs in conventional PSCs with a FA(0.9)MA(0.1)Pb(I0.9Br0.1)(3) . 0.05 CsI perovskite, respectively. Thereinto, the champion device based on doped K-DHP-1 exhibits a power conversion efficiency (PCE) of up to 20.52% with J(sc) of 23.96 mA/cm(2), V-oc of 1.09 V and FF of 78.6%, rivalling the performance of device fabricated with spiro-OMeTAD (20.97%). More encouragingly, the K-DHP-1-based PSC displays good long-term stability, remaining 88% of its original performance after storing in atmosphere (30%similar to 50% relative humidity) for 45 d without encapsulation, which is better than the spiro-OMeTAD-based PSC. These results indicate that K-DHP-1 can be an effective HTM to realize high efficiency and stable PSCs, and furthermore DHP can serve as an excellent building block for the development of new HTMs in the future.