Quinoidal 2,2′, 6,6′-Tetraphenyl-Dipyranylidene as a Dopant-Free Hole-Transport Material for Stable and Cost-Effective Perovskite Solar Cells

We report on the use of 2,2', 6,6'-tetraphenyldipyranylidene (DIPO-Ph-4), a large quinoidal planar pi-conjugated heterocycle, as a simple, easy-to-synthetize, and efficient dopant-free hole-transport material in perovskite solar cells (PSCs). PSCs using pristine DIPO-Ph-4 show photon conversion efficiencies up to 10.1%, which is higher than a PSC utilizing dopantfree spiro-OMeTAD (5.1%). DIPO-Ph-4-based PSCs exhibit a short-circuit current density of 19.52 mA cm(-2) and an open-circuit voltage of 0.933 V, values that are superior to dopantfree spiro-OMeTAD and comparable to doped spiroOMeTAD. These better performances find their origin in a higher HOMO level (-4.74 eV) and a much higher hole mobility (2 X 10(-2) cm(2)V(-1) s(-1)). Finally, PSCs based on DIPO-Ph-4 possess a superior stability compared to doped-spiroOMeTAD-based devices when tested over 600 h.