Interfacial and bulk properties of hole transporting materials in perovskite solar cells: spiro-MeTAD versus spiro-OMeTAD
Résumé
Two spiro-MeTAD compounds (1 and 2) were synthesized, characterized by experimental and quantum
mechanical methods, and used as hole transporting materials (HTMs) in perovskite solar cells (PSCs). The
new compounds differ from spiro-OMeTAD only by the presence of methyl substituents as compared to
methoxy groups. This modification results in the absorption band blue shifting by 20 nm as compared
to spiro-OMeTAD, increased glass transition temperature for 2, and reduced ionization potentials by
0.02–0.12 eV. Hole mobilities five times larger were obtained for spiro-MeTAD/spiro-MeTAD, which is
maintained in the presence of additives. Despite this improvement, J–V measurements in PSCs resulted
in a power conversion efficiency (PCE) of 17.2% and 17.05% for 1 and 2 HTMs, respectively, as compared
to 19.24% for spiro-OMeTAD. Photoluminescence measurements of perovskite:HTM layers indicate
much stronger quenching in the case of spiro-OMeTAD/spiro-MeTAD. These results point to the
dominant importance of the perovskite:HTM interfacial properties as compared to the HTM holetransport properties in the bulk. Given that improved hole-mobility and energy-level alignment are the
main targets of the current research efforts in this domain, our results alert to the necessity to prioritize
the improvement of perovskite–HTM interaction properties.
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