The micellization process of the aqueous mixed system Triton X-100 (TX100) -Dodecyltrimethylammonium Bromide (DTAB) was studied with a battery of procedures: surface tension, static and dynamic light scattering and ion-selective electrodes. Results were also analysed with two thermodynamic procedures. The system shows some changes in its behaviour with changing the mole fraction of DTAB, DTAB, in the whole surfactant mixture. For DTAB 0.40 micelles are predominantly TX100 with scarce solubilized DTA + ions, and TX100 acts as a nearly ideal solvent. In the range 0.50 DTAB 0.75 it seems that none of the components acts as a solvent, and above DTAB 0.75 there are abrupt changes in the size and electrophoretic mobility of micelles.These phenomena have been interpreted in the light of the thermodynamic results and some TX100-ionic surfactant mixtures of literature.
The relatively low
stability of solar cells based on hybrid halide
perovskites is the main issue to be solved for the implementation
in real life of these extraordinary materials. Degradation is accelerated
by temperature, moisture, oxygen, and light and mediated by halide
easy hopping. The approach here is to incorporate pristine graphene,
which is hydrophobic and impermeable to gases and likely limits ionic
diffusion while maintaining adequate electronic conductivity. Low
concentrations of few-layer graphene platelets (up to 24 × 10
–3
wt %) were incorporated to MAPbI
3
films
for a detailed structural, optical, and transport study whose results
are then used to fabricate solar cells with graphene-doped active
layers. The lowest graphene content delays the degradation of films
with time and light irradiation and leads to enhanced photovoltaic
performance and stability of the solar cells, with relative improvement
over devices without graphene of 15% in the power conversion efficiency,
PCE. A higher graphene content further stabilizes the perovskite films
but is detrimental for in-operation devices. A trade-off between the
possible sealing effect of the perovskite grains by graphene, that
limits ionic diffusion, and the reduction of the crystalline domain
size that reduces electronic transport, and, especially, the detected
increase of film porosity, that facilitates the access to atmospheric
gases, is proposed to be at the origin of the observed trends. This
work demonstrated how the synergy between these materials can help
to develop cost-effective routes to overcome the stability barrier
of metal halide perovskites, introducing active layer design strategies
that allow commercialization to take off.
MA0.5FA0.5PbI3, increasing the average photoconversion efficiency (PCE) respect the reference cell by 18, 32 and 4 % respectively, observed for regular, n-i-p, and inverted, p-i-n, solar cell configurations. This analysis highlights the generality of this approach for halide perovskite materials in order to reduce non-radiative recombination as observed by impedance spectroscopy.
Interfaces between photoactive perovskite layer and selective contacts play a key role in the performance of perovskite solar cells (PSCs). The properties of the interface can be modified by the introduction of molecular interlayers between the halide perovskite and the transporting layers. Herein, two novel structurally related molecules, 1,3,5-tris(α-carbolin-6-yl)benzene (TACB) and the hexamethylated derivative of truxenotris(7azaindole) (TTAI), are reported. Both molecules have the ability to self-assemble through reciprocal hydrogen bond interactions, but they have different degrees of conformational freedom. The benefits of combining these tripodal 2D-self-assembled small molecular materials with well-known hole transporting layers (HTLs), such as PEDOT:PSS and PTAA, in PSCs with inverted configuration are described. The use of these molecules, particularly the more rigid TTAI, enhanced the charge extraction efficiency and reduced the charge recombination. Consequently, an improved photovoltaic performance was achieved in comparison to the devices fabricated with the standard HTLs.
Halide perovskite nanocrystals (PNCs) exhibit growing attention in optoelectronics due to their fascinating color purity and improved intrinsic properties. However, structural defects emerging in PNCs progressively hinder the radiative recombination and carrier transfer dynamics, limiting the performance of light-emitting devices. In this work, we explored the introduction of guanidinium (GA + ) during the synthesis of high-quality Cs 1−x GA x PbI 3 PNCs as a promising approach for the fabrication of efficient bright-red light-emitting diodes (R-LEDs). The substitution of Cs by 10 mol % GA allows the preparation of mixed-cation PNCs with PLQY up to 100% and long-term stability for 180 days, stored under air atmosphere and refrigerated condition (4 °C). Here, GA + cations fill/replace Cs + positions into the PNCs, compensating intrinsic defect sites and suppressing the nonradiative recombination pathway. LEDs fabricated with this optimum material show an external quantum efficiency (EQE) near to 19%, at an operational voltage of 5 V (50−100 cd/m 2 ) and an operational half-time (t 50 ) increased 67% respect CsPbI 3 R-LEDs. Our findings show the possibility to compensate the deficiency through A-site cation addition during the material synthesis, obtaining less defective PNCs for efficient and stable optoelectronic devices.
This study highlights that PbS QDs stabilize the target 15% guanidinium based perovskite solar cells due to a synergic combination of compressive strain and volume expansion of the MAPbI3 perovskite unit crystal cells.
Two hundred sixty-six films processed with flash infrared annealing were optically and structurally characterized. We determine the optimum conditions for the formation of the mixed-cations halide perovskite active phase.
Defects in polycrystalline halide perovskite films can cause a decrease of the solar cell photoconversion efficiency and stability. The perovskite film enhanced during crystal growth by controlling the processing method can alleviate defects and the related recombination sites that affect the performance of cells. Herein, flash infrared annealing is employed to crystallize methylammonium lead iodide perovskite with a single heating pulse, where uniform grain domains are optically observed and mapped. Films are annealed with different temperature ramps up to 48 °C s−1 heating rate. Annealing with higher heating rates presents lower defect densities, decreases the Urbach energy tail, and improves the optoelectrical performance of the films. These improvements are rationalized by Raman spectroscopy of nucleation points and grain surface differences among the process variations. The role of crystal growth and subsequent film quality allows to achieve a champion photovoltaic device growth at 48 °C s−1 with stability around 250 h under 1 sun illumination and 60% relative humidity for 100 h under 3 sun (AM1.5G) illumination. In situ optical imaging is recorded during the process, confirming that rapid annealing, i.e., higher heating rates, contributes to obtain more stable devices with the added advantage of shorter processing time.
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