A linear D-π-A based hole transport material for high performance rigid and flexible planar organic-inorganic hybrid perovskite solar cells

A facile and less expensive hole transport material is essential to enhance the power conversion efficiency (PCE) of perovskite solar cells (PSC) without compromising the ambient stability. Here, we designed and synthesized a new class of HTM by introducing donor-π-acceptor (D-π-A). The HTM was synthesized by combining the moieties of triphenylamine, biphenyl and oxadiazole derivatives as electron donating, π-spacer and electron withdrawing moieties, respectively, named as 4'''-(5-(4-(hexyloxy)phenyl)-1,3,4-oxadiazol-2-yl)-N,N-bis(4-methoxyphenyl)-[1,1':4',1'':4'',1'''-quaterphenyl]-4-amine (TPA-BP-OXD). The π-π conjugation is increased by introducing biphenyl π-spacer. The HTM was terminated with OXD-based moiety and framed it as a D-π-A-based HTM that trigged to improve the transportation charging properties due to its π-π interactions. We rationally investigated the HTM by characterizing its photophysical, thermal, electrochemical, and charge transport properties. The great features of HTM stimulated us to explore on rigid and flexible substrates as dopant-free HTM in planar inverted-perovskite solar cells (i-PSCs). The device performance in solution processed i-PSCs on both rigid and flexible substrates and dopant-free HTM based device showed PCEs of 15.46% and 12.90%, respectively. The hysteresis is negligible, which is one of the most effective results based on TPA-BP-OXD HTM in planar i-PSCs. The device performance and stability based on TPA-BP-OXD HTM is better due to higher extraction and transportation of holes from the perovskite material, reduced charge recombination at the interface, and enhanced hydrophobicity of HTM to compete for a role in enhancing the stability. Overall, our findings demonstrate the potentiality of TPA-BP-OXD based HTM in planar i-PSCs.