Multifunctional organic semiconductor for dopant-free perovskite solar cells

Replacing the orthogonal molecular core in 2,2 & PRIME;,7,7 & PRIME;-Tetrakis[N,N-di(4-methoxyphenyl)amino]- 9,9 & PRIME;-spirobi-fluorene (spiro-OMeTAD) with pi-conjugated functional group is a promising strategy for designing of dopant-free hole transport materials (HTMs) for perovskite solar cells (PSCs). Here, an organic molecule with 9-fluorenone core, namely TPA-9F (2,7-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-9 H-fluoren-9-one), which featuring with excellent intermolecualr and interlayer interaction, was successfully developed and applied in PSCs. It's found that TPA-9F shows multifunctional characteristics, such as close interlayer interaction with perovskite surface, strong hole transport capacity and hydrophobicity. As a result, mesoscopic n-i-p structured PSCs employing dopant-free TPA-9F as HTM exhibit a high efficiency of 18.40%, which is much higher than that using dopant-free spiro-OMeTAD (9.38%). This work demonstrate the great potential of pi-conjugated functional group in designing efficient organic p-type semiconductors for dopant-free PSCs.