perovskites incorporating hydrophobic organic spacer cations show improved film stability and morphology compared to their three-dimensional (3D) counterparts. However, 2D perovskites usually exhibit low photoluminescence quantum efficiency (PLQE) owing to strong exciton-phonon interaction at room temperature, which
Amelioration of the mobility and, in particular, the thermal stability of a hole-transporting molecular semiconductor is a practicable strategy to attain the enhancement of both power conversion efficiency (PCE) and operational durability of perovskite solar cells (PSCs). Here a cost-effective double-[4]helicene-based molecular semiconductor (DBC-OMeDPA) is synthesized for a solution-deposited thin film, exhibiting an improved hole mobility in comparison with state-of-the-art spiro-OMeTAD control. X-ray crystallographic analysis and theoretical calculation reveal the three-dimensional molecular stacking and multidirectional hole-transporting property of DBC-OMeDPA, clarifying the microscopic mechanism of the hole-transport process. A better PCE of 22% at the AM 1.5G conditions is achieved for PSCs with DBC-OMeDPA as the hole-transporter. Moreover, PSCs using DBC-OMeDPA characteristic of an elevated intrinsic glass transition temperature of 154 °C maintain a stable PCE output for hundreds of hours at 60 °C under equivalent full sunglight soaking.
Clarifying the structural basis and
microscopic mechanism lying
behind electronic properties of molecular semiconductors is of paramount
importance in further material design to enhance the performance of
perovskite solar cells. In this paper, three conjugated quasilinear
segments of 9,9-dimethyl-9H-fluorene, 9,9-dimethyl-2,7-diphenyl-9H-fluorene, and 2,6-diphenyldithieno[3,2-b:2′,3′-d]thiophene are end-capped
with two bis(4-methoxyphenyl)amino groups for structurally simple
molecular semiconductors Z1, Z2, and Z3, which crystallize in the
monoclinic
P
21/n, triclinic P1̅, and monoclinic
C
2/
c
space
groups, respectively. The modes and energies of intermolecular noncovalent
interactions in various closely packed dimers extracted from single
crystals are computed based on the quantum theory of atoms in molecules
and energy decomposition analysis. Transfer integrals, reorganization
energies, and center-of-mass distances in these dimers as well as
band structures of single crystals are also calculated to define the
theoretical limit of hole transport and microscopic transport pictures.
Joint X-ray diffraction and space-charge-limiting current measurements
on solution-deposited films suggest the dominant role of crystallinity
in thin-film hole mobility. Photoelectron spectroscopy and photoluminescence
measurements show that an enhanced interfacial interaction between
the perovskite and Z3 could attenuate the adverse impact of reducing
the energetic driving force of hole extraction. Our comparative studies
show that the molecular semiconductor Z3 with a properly aligned highest
occupied molecular orbital energy level and a high thin-film mobility
can be employed for efficient perovskite solar cells, achieving a
good power conversion efficiency of 20.84%, which is even higher than
that of 20.42% for the spiro-OMeTAD control.
Ionic organic-inorganic hybrid lead halide perovskites are prone to degrade at elevated temperatures, especially in the presence of water moisture. This grand challenge heavily impedes the outdoor application of high-efficiency...
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