Conjugated polymers of an oxa[5]helicene-derived polycyclic heteroaromatic: tailoring energy levels and compatibility for high-performance perovskite solar cells.

In the quest to enhance the efficiency and durability of n-i-p perovskite solar cells (PSCs), engineering hole-transporting conjugated polymers with well-matched energy levels, exceptional film-forming properties, rapid hole transport, and superior moduli is paramount. Here, we present a novel approach involving the customization of a conjugated polymer, designated as p-DTPF4-EBEH, comprising alternating units of an oxa[5]helicene-based polycyclic heteroaromatic (DTPF4) and 5,5'-(2,5-di(hexyloxy)-1,4-phenylene)bis(3,4-ethylenedioxythiophene) (EBEH), synthesized through palladium-catalyzed direct arylation. Relative to homopolymers p-DTPF4 and p-EBEH, p-DTPF4-EBEH demonstrates a proper HOMO energy level, hole density, and hole mobility, alongside superior film-forming capabilities. Remarkably, compared to the commonly used hole transport material spiro-OMeTAD, p-DTPF4-EBEH not only exhibits superior film-forming property and hole mobility but also offers increased modulus and improved waterproofing. Incorporating p-DTPF4-EBEH as the hole transport material in PSCs results in an average power conversion efficiency of 25.8%, surpassing the 24.3% achieved with spiro-OMeTAD. Importantly, devices utilizing p-DTPF4-EBEH demonstrate enhanced thermal storage stability at 85 °C, along with operational robustness.

Durable Perovskite Solar Cells with 24.5% Average Efficiency: The Role of Rigid Conjugated Core in Molecular Semiconductors.

Efficient and robust n-i-p perovskite solar cells necessitate superior organic hole-transport materials with both mechanical and electronic prowess. Deciphering the structure-property relationship of these materials is crucial for practical perovskite solar cell applications. Through direct arylation, two high glass transition temperature molecular semiconductors, DBC-ETPA (202 °C) and TPE-ETPA (180 °C) are synthesized, using dibenzo[g,p]chrysene (DBC) and 1,1,2,2-tetraphenylethene (TPE) tetrabromides with triphenylene-ethylenedioxythiophene-dimethoxytriphenylamine (ETPA). In comparison to spiro-OMeTAD, both semiconductors exhibit shallower HOMO energy levels, resulting in increased hole densities (generated by air oxidation doping) and accelerated hole extraction from photoexcited perovskite. Experimental and theoretical studies highlight the more rigid DBC core, enhancing hole mobility due to reduced reorganization energy and lower energy disorder. Importantly, DBC-ETPA possesses a higher cohesive energy density, leading to lower ion diffusion coefficients and higher Young's moduli. Leveraging these attributes, DBC-ETPA is employed as the primary hole-transport layer component, yielding perovskite solar cells with an average efficiency of 24.5%, surpassing spiro-OMeTAD reference cells (24.0%). Furthermore, DBC-ETPA-based cells exhibit superior operational stability and 85 °C thermal storage stability.

In Situ Formation of Compact PbI2 Shell Boosts the Efficiency and Thermostability of Perovskite 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.

Unraveling the Structure-Property Relationship of Molecular Hole-Transporting Materials for Perovskite Solar Cells.

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 P21/n, triclinic P1̅, and monoclinic C2/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.