Inducing hybrid perovskite crystal growth on substrates for efficient, ambient stable optoelectronic devices

Hybrid lead perovskites are at the forefront of the emerging class of optoelectronic materials. With a certified photovoltaic efficiency of 25.2 % for 9 mm2 area devices, it is currently the most efficient emerging photovoltaic technology. The lion’s share of perovskite photovoltaic devices employs polycrystalline thin films of this material, with typical grain sizes around 300 nm. The optoelectronic characteristics like trap density and carrier lifetimes are several orders of magnitude better in perovskite single crystals, suggesting that these materials have the potential to deliver higher power conversion efficiencies than their polycrystalline film counterparts. Even though there are a plethora of reports on polycrystalline devices, works on monocrystalline perovskite photovoltaic cells are scanty, owing to their difficulties in device fabrication procedures. For the fabrication of efficient single crystal-based devices, the crystals need to be sliced into wafers of thickness typically lesser than the diffusion length of charge carriers (of the order of 100 μm). As this material is brittle and has a low shear modulus (of the order 10 GPa), it cannot be sliced down to these thickness regimes. Therefore, the only viable option to fabricate a single crystal/highly-crystalline hybrid perovskite device is to grow the crystals of these materials directly on the device substrates. Photovoltaic devices fabricated using methylammonium lead iodide (MAPbI3) monocrystalline films have yielded efficiencies of 21 % for a device area of 2 mm2; however, scaling beyond a few millimeters in lateral dimensions is yet to be achieved. In this work, two techniques were developed to grow highly crystalline layers of MAPbI3 films over substrates, without any constraint over their lateral dimensions. The mechanism of anti-solvent vapor crystallization (AVC) of lead halide perovskites was meticulously investigated, and sonication modified AVC (S-AVC) was developed. As the nucleation and initial crystal growth were initiated by sonication, this crystal growth technique was independent of the nature of substrates and their surfaces. The grain sizes of these films were around 100 micrometers, three orders of magnitude higher than standard polycrystalline thin films. These highly crystalline films were utilized to fabricate planar photodetectors with a responsivity of 20 AW-1, 1000 times higher than that of polycrystalline thin film-based devices. The thicknesses of S-AVC based films were of the order of hundred micrometers and were crystallographically random-oriented, making it inappropriate to fabricate vertical optoelectronic devices. In order to overcome these shortcomings of the technique, a second method was developed by modifying the standard spin-coating procedure used to deposit perovskite thin films. The perovskite precursor chemistry was tuned, and crystallization kinetics were optimized for inducing heterogeneous nucleation and growth of spherulitic perovskite crystals on substrate surfaces. These films were compact and pinhole-free with grain sizes above 100 micrometers. The film thicknesses were easily controllable to a few hundred nanometers by varying the spin coating parameters and the films were highly oriented along [200], [224] crystallographic planes, thus befitting it for vertical photovoltaic device fabrication. The fabricated photovoltaic cells exhibited superior room ambient stability along with good photoconversion efficiencies above 15 %, owing to the enhanced crystallinity of the perovskite layer. The films of various levels of crystallinity were used to unveil the role of grain boundaries on the ambient stability of the material. It was proved that a reduction in the number of grain boundaries hampers the moisture-induced degradation, thus can be used as an alternative strategy to enhance the ambient stability of perovskite-based optoelectronic devices. Lead halide perovskites are known mixed ionic-electronic conductors and the films of various levels of crystallinity were used to study the effect of grain boundaries on ionic motion through the material. In comparison to standard thin films, the ionic conductance was 100 times higher in S-AVC based films which demonstrated that grain boundaries can reduce ionic and electronic conductance by blocking the charge transport through the material. In a nutshell, two techniques were developed in this thesis to grow highly crystalline layers of hybrid lead halide perovskites over substrates. The grown films were utilized to study the effect of crystallinity on optoelectronic device characteristics, ionic conductance, and moisture stability of the material.Doctor of Philosoph

Differential and Integral Equations for the 3-Variable Hermite-Frobenius-Euler and Frobenius-Genocchi Polynomials

The main goal of the present article is to derive some new classes of differential equations including partial and integrodifferential equations for the 3-variable Hermite-Frobenius-Euler and Frobenius-Genocchi polynomials by use of the factorization method. We also perform a further investigation for aforementioned polynomials and derive corresponding homogeneous Volterra integral equations. The differential equations for these families of polynomials contain, as their special cases, the differential equations for some known special polynomials. Moreover, the inclusion of integral equations is a new and recent investigation which adds some extra attention to these polynomials

INTEGRASI MANAJEMEN KURIKULUM SEBAGAI UPAYA PENINGKATAN MUTU PEMBELAJARAN DI SEKOLAH

The purpose of this study was to determine the integration of curriculum management in Roushon Fikr Islamic Elementary School Jombang in improving the quality of learning. The locus of this research was taken, because SDI Roushon Fikr is an Islamic educational institution that was present in the era of the industrial revolution 4.0, and is located in the santri city of Jombang as the basis of a large Islamic boarding school in East Java. The research method used is a qualitative descriptive approach, with data mining techniques through observation, interviews, and relevant documentation as secondary data. The results showed that; first, planning the curriculum at SDI Roushon Fikr carefully and structured at the beginning of each year, but still needs to align the process of preparing the lesson plan (RPP), syllabus, and learning tools that are adjusted to the educational calendar and effective week; second, the organization of learning at SDI Roushon Fikr is carried out by representatives of the school in the field of curriculum, through the stage of division of responsibilities for each teacher that is relevant to the field of expertise of each teacher; third, the implementation of the curriculum and the relevance of the quality of learning at SDI Roushon Fikr, starting with opening activities, core activities, and closing activities; fourth, the monitoring and evaluation of the curriculum is carried out by the principal through supervising the school representatives in the curriculum field and the subject teachers in every semester and every year

Solution grown double heterostructure on large hybrid halide perovskite crystal

Heterostructure is playing a crucial role in current optoelectronic applications. Realizing the heterostructure in a recently exciting semiconductor material: hybrid halide perovskite crystals, has been a long-sought goal in the field. Here, we demonstrate modulation-doped layer growth on large hybrid halide perovskite crystals. We show that the well known problem of halide ion inter-diffusion can be controlled by (1) using low halide composition gradient and (2) adjusting solution concentrations just above the critical supersaturation, in the solvo-thermal liquid-phase growth process. In comparison to few seconds dipping time previously reported for ion exchange processes, our layer growth time could be conveniently extended up to 80 minutes to grow a uniform and controllable layer, with a very thin inter-diffusion region. The growth of CH3NH3PbBr3 layer on top of CH3NH3Pb(Br0.85Cl0.15)3 bulk substrate is studied for different growth times to obtain up to 30µm layer thickness. Ion diffusion profile and layer thickness are verified respectively by cross sectional characterization using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS). Electron Back-Scattering Diffraction (EBSD) suggests the similar crystallographic orientation for both substrate and grown layers. Our diffusion model illustrates the halide ion concentration at the interface, reflecting the EDS mapping results. Optical imaging and Photoluminescence (PL) characterization confirm the quality and the bandgap of the grown layers. Especially, the growth process is further extended for two consecutive layers to create a double heterostructure for the first time with a large perovskite crystal. Our low cost process could pave the way for many optoelectronic applications such as color tune-able light emitting diodes or photodetectors to be developed with perovskite crystals.MOE (Min. of Education, S’pore)Accepted versio

Integrating Curriculum Management Into School-based Learning Quality Improvement

The purpose of this study was to determine the integration of curriculum management in Roushon Fikr Islamic Elementary School Jombang in improving the quality of learning. The locus of this research was taken, because SDI Roushon Fikr is an Islamic educational institution that was present in the era of the industrial revolution 4.0, and is located in the santri city of Jombang as the basis of a large Islamic boarding school in East Java. The research method used is a qualitative descriptive approach, with data mining techniques through observation, interviews, and relevant documentation as secondary data. The results showed that; first, planning the curriculum at SDI Roushon Fikr carefully and structured at the beginning of each year, but still needs to align the process of preparing the lesson plan (RPP), syllabus, and learning tools that are adjusted to the educational calendar and effective week; second, the organization of learning at SDI Roushon Fikr is carried out by representatives of the school in the field of curriculum, through the stage of division of responsibilities for each teacher that is relevant to the field of expertise of each teacher; third, the implementation of the curriculum and the relevance of the quality of learning at SDI Roushon Fikr, starting with opening activities, core activities, and closing activities; fourth, the monitoring and evaluation of the curriculum is carried out by the principal through supervising the school representatives in the curriculum field and the subject teachers in every semester and every year

Crown Ethers Enable Room Temperature Synthesized CsPbBr3 Quantum Dots for Light-Emitting Diodes

The synthesis of all-inorganic cesium lead halide perovskite quantum dots (QDs) typically requires high temperatures, stringent conditions, large quantities of surface ligands, and judicious purification steps to overcome ligand-induced charge injection barriers in optoelectronic devices. Low-temperature syntheses generally require lower ligand concentrations, but are severely limited by the low solubility of the Cs precursor. We describe an innovative and general approach under ambient conditions to overcome these solubility limitations, by employing crown ethers. The crown ethers facilitate complete dissolution of the CsBr precursor, rendering CsPbBr3 QD inks practical for device fabrication. The resultant LEDs displayed bright green emission, with a current efficiency, and external quantum efficiency of 9.22 cd A-1 and 2.64%, respectively. This represents the first LED based on CsPbBr3 QDs prepared at room temperature. Lastly, the crown ethers form core-shell structures, opening new avenues to exploit their strong coordination strength.NRF (Natl Research Foundation, S’pore)Accepted versio

Perturbation-induced seeding and crystallization of hybrid perovskites over surface-modified substrates for optoelectronic devices

Growing a monocrystalline layer of lead halide perovskites directly over substrates is necessary to completely harness their stellar properties in optoelectronic devices, as the single crystals of these materials are extremely brittle. We study the crystallization mechanism of perovskites by antisolvent vapor diffusion to its precursor solution and find that heterogeneous nucleation prevails in the process, with the crystallization dish walls providing the energy to overcome the nucleation barrier. By perturbing the system using sonication, we are able to introduce homogeneously nucleated seed crystals in the precursor solution. These seeds lead to the growth of closely packed crystals over surface-modified substrates kept in the precursor solution. This crystallization process is substrate independent and scalable and can be utilized to fabricate planar optoelectronic devices. We demonstrate a methylammonium lead iodide planar crystal photoconductor with a colossal detectivity of 1.48 × 1013 Jones.NRF (Natl Research Foundation, S’pore)Accepted versio

Crown Ethers Enable Room-Temperature Synthesis of CsPbBr₃ Quantum Dots for Light-Emitting Diodes

The synthesis of all-inorganic cesium lead halide perovskite quantum dots (QDs) typically requires high temperatures, stringent conditions, large quantities of surface ligands, and judicious purification steps to overcome ligand-induced charge injection barriers in optoelectronic devices. Low-temperature syntheses generally require lower ligand concentrations but are severely limited by the low solubility of the Cs precursor. We describe an innovative and general approach employing crown ethers under ambient conditions to overcome these solubility limitations. The crown ethers facilitate complete dissolution of the CsBr precursor, rendering CsPbBr₃ QD inks practical for device fabrication. The resultant light-emitting diodes (LEDs) displayed bright green emission, with a current efficiency and external quantum efficiency of 9.22 cd A^–1 and 2.64%, respectively. This represents the first LED based on CsPbBr₃ QDs prepared at room temperature. Lastly, the crown ethers form core–shell structures, opening new avenues to exploit their strong coordination strength

Solution-processed, highly crystalline, and oriented MAPbI₃ thin films by engineering crystal-growth kinetics

Growing oriented and monocrystalline layers of lead halide perovskites over device substrates helps to harness their outstanding optoelectronic properties. Epitaxial growth of lead halide perovskites for device fabrication is limited by the lack of lattice-matched substrates and the requirement of compact pinhole-free films. Most optoelectronic devices use amorphous substrates, hindering oriented epitaxial growth. Here, we demonstrate highly crystalline methylammonium lead iodide (MAPbI3) thin films over amorphous substrates by meticulously optimizing the nucleation and growth kinetics in spin coating. The "epitaxial-like" films enable large-area crystalline layer fabrication, with larger than 100 μm spherulitic grains oriented along [200] and [224] planes. The compact, highly crystalline, and oriented films of MAPbI3 formed over ITO/SnO2 are used to fabricate perovskite solar cells (PSCs) with an area of 1 cm2. Despite the perovskite films being highly oriented and crystalline, the PSCs’ performances highlight the critical role the interfaces play in photovoltaic cells.Ministry of Education (MOE)Submitted/Accepted versionThe authors would like to acknowledge that this research is supported bythe Ministry of Education (MOE) under the grant no. MOE-T2EP50221-003