Multifunctional organic semiconductor for dopant-free perovskite solar cells

Replacing the orthogonal molecular core in 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]− 9,9′-spirobifluorene (spiro-OMeTAD) with π-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 π-conjugated functional group in designing efficient organic p-type semiconductors for dopant-free PSCs. •A HTM with desired molecular planarity and close interlayer interaction with perovskite surface.•The hole mobility improved significantly by replacing the cross-linked core in the spiro-OMeTAD with 9-fluorenone.•The PSCs based on dopant-free TPA-9 F achieve a PCE of 18.40%.