Bat-El Cohen

Parameters Influencing the Deposition of Methylammonium Lead Halide Iodide in Hole Conductor Free Perovskite-Based Solar Cells

Perovskite is a promising light harvester for use in photovoltaic solar cells. In recent years, the power conversion efficiency of perovskite solar cells has been dramatically increased, making them a competitive source of renewable energy. An important parameter when designing high efficiency perovskite-based solar cells is the perovskite deposition, which must be performed to create complete coverage and optimal film thickness. This paper describes an in-depth study on two-step deposition, separating the perovskite deposition into two precursors. The effects of spin velocity, annealing temperature, dipping time, and methylammonium iodide concentration on the photovoltaic performance are studied. Observations include that current density is affected by changing the spin velocity, while the fill factor changes mainly due to the dipping time and methylammonium iodide concentration. Interestingly, the open circuit voltage is almost unaffected by these parameters. Hole conductor free perovskite solar cells are used in this work, in order to minimize other possible effects. This study provides better understanding and control over the perovskite deposition through highly efficient, low-cost perovskite-based solar cells.

High efficiency quasi 2D lead bromide perovskite solar cells using various barrier molecules

This work reports on the high power conversion efficiency (PCE) and high open circuit voltage (Voc) of bromide-based quasi 2D perovskite solar cells. A Voc of more than 1.4 V and, at the same time, a PCE of 9.5% for cells with hole transport material (HTM) were displayed, whereas a Voc value of 1.37 V and a PCE of 7.9% were achieved for HTM-free cells. Bromide quasi 2D perovskites were synthesized using various long organic barriers (e.g., benzyl ammonium, BA; phenylethyl ammonium, PEA; and propyl phenyl ammonium, PPA). The influence of different barrier molecules on the quasi 2D perovskites properties was studied using absorbance, X-ray diffraction, and scanning electron microscopy. No change was observed in the exciton binding energy as a result of changing the barrier molecule. Density functional theory (DFT) with spin–orbit coupling calculations showed that in the case of BA, holes are delocalized over the whole molecule, whereas for PEA and PPA, they are delocalized more at the phenyl ring. This factor influences the electrical conductivity of holes, which is highest for BA in comparison with the other barriers. In the case of electrons, the energy onset for the nonzero conductivity is lowest for BA. Both calculations support the better PV performance observed for the quasi 2D perovskite based on BA as the barrier. Finally, using contact angle measurements, it was shown that the quasi 2D perovskite is more hydrophobic than the 3D perovskite. Stability measurements showed that cells based on the quasi 2D perovskite are more stable than cells based on the 3D perovskite.

Self‐Assembly of Perovskite for Fabrication of Semitransparent Perovskite Solar Cells

DOI: 10.1002/admi.201500118 layer was deposited by evaporation technique. However, evaporation-based processes are very costly, require high capital investments, and are very complicated for upscaling, which is required for industrial applications. Semitransparent top electrode made of silver nanowires was introduced into perovskite-based solar cells. [ 24 ] The transparency in this case was controlled by the top electrode transparency and not by the perovskite fi lm. In addition, the silver nanowires can be used as an alternative top electrode made by solution-processed technique for semitransparent solar cells. Here, we report on a unique, simple wet deposition method for the fabrication of semitransparent perovskite-based solar cells. This deposition method is fundamentally different from previously reported deposition methods of CH 3 NH 3 PbI 3 (MAPbI 3 ) perovskite. The fi lm formation in this method is enabled by the mesh-assisted assembly of the perovskite solution through wetting along the wall of a conventional screen printing mesh, as described earlier. [ 25–27 ] Meaning, here the perovskite is deposited along a controlled pattern through solution-process and in ambient conditions. Semitransparent perovskite solar cells were fabricated; the perovskite grid was deposited upon a mesoporous TiO 2 layer, followed by 2,2′,7,7′-tetrakis-( N , N -di-4methoxyphenylamino)-9,9′-spirobifl uorene (spiro-OMeTAD) deposition and evaporation of gold back contact. In addition, semitransparent hole conductor free perovskite solar cells (without spiro-OMeTAD as the hole transporting material (HTM)) were prepared for comparison. Nontransparent HTM-free perovskite solar cells were already demonstrated to achieve 10.85% effi ciency. [ 26–29 ] Control of transparency is achieved by changing solution concentrations (wt%) and mesh openings of the printing screen. Using this method, semitransparent cells with 20–70% transparency were fabricated. Ultrahigh resolution scanning electron microscopy (UHR-SEM), optical microscope, and a profi lometer were used to characterize the perovskite grids. Intensity-modulated photovoltage spectroscopy (IMVS) was performed for the analysis of the recombination processes occurring in this unique structure of semitransparent perovskite solar cells.

Fully 2D and 3D printed anisotropic mechanoluminescent objects and their application for energy harvesting in the dark

We report on new material compositions enabling fully printed mechanoluminescent 3D devices by using a one-step direct write 3D printing technology. The ink is composed of PDMS, transition metal ion-doped ZnS particles, and a platinum curing retarder that enables a long open time for the printing process. 3D printed mechanoluminescent multi-material objects with complex structures were fabricated, in which light emission results from stretching or wind blowing. The multi-material printing yielded anisotropic light emission upon compression from different directions, enabling its use as a directional strain and pressure sensor. The mechanoluminescent light emission peak was tailored to match that of a perovskite material, and therefore, enabled the direct conversion of wind power in the dark into electricity, by linking the printed device to perovskite-based solar cells.