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...
Despite the efficiency comparable to crystalline silicon photovoltaics, it is still a severe concern on the long-term stability under the stress of heat, light, and bias potential for perovskite solar cell (PSC).Here, we report a triple aza[6]helicene-based molecular semiconductor (TBTA[6]H) characteristic of a fully fused conjugated backbone. TBTA[6]H presents superior solubility and glass-transition temperature (T g ). An airdoped composite of TBTA[6]H with a high electrical conductivity of 353 μS cm −1 is still featured by a T g of 112 °C, enabling the fabrication of 22% efficiency, 85 °C durable PSCs. The TBTA[6]H composite not only exhibits an excellent morphology stability at 85 °C in PSCs, but also remarkably attenuates the thermal degradation of photoactive perovskite layer. The cell with TBTA[6]H also displays an excellent operation stability under the continuous full sunlight soaking at 55 °C.
Organic-inorganic hybrid perovskites in high-efficiency solar cells are prone to degradation at elevated temperatures, especially in the presence of water moisture. A hole-transporting conjugated copolymer (abbreviated as p-NP-E) characteristic of alternating N-annulated perylene and 3,4-ethylenedioxythiophene backbones, to achieve thermostable perovskite solar cells (PSCs) via controlling gas permeation and thus perovskite decomposition is reported. p-NP-E can be conveniently prepared via Pd-catalyzed direct arylation polycondensation. The air-doped p-NP-E composite film containing nonvolatile 4-tert-butylpyridinium bis(trifluoromethanesulfonyl)imide presents a higher hole mobility and an improved conductivity in comparison with the control based on the state-of-the-art polymer, p-TAA, leading to more efficient PSCs. More critically, the p-NP-E based hole transport layer is not only morphologically more heat-resistant, but also features a lower solubility coefficient and diffusion coefficient of both environmental water molecules and gaseous products such as CH 3 I and CH 3 NH 2 from the thermal decomposition of perovskite, enabling the fabrication of 21.7%-efficiency, 85 °C durable solar cells.
Judicious tailoring of a robust interlayer is central to maintain the durable operation of optoelectronic devices. In this paper, an ultrathin, compact, and uniform PbI2 shell on the surface of perovskite via the method of ZnI2 aided in situ transformation is produced. The resultant PbI2 interlayer can prolong the excited‐state lifetime of perovskite and attenuate the recombination kinetics of separated charges, leading to an improvement of power conversion efficiency up to 22.5% for perovskite solar cells (PSCs) at the AM 1.5G conditions. Moreover, the PSC with PbI2 interlayer exhibits an enhanced thermostability, retaining 87% of initial efficiency after aging at 60 °C for 1000 h.
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