Morphology Control of Photoactive Layer for Highly Efficient Perovskite solar cells

Department of Energy EngineeringConsiderable effort to develop renewable energy sources has been expended over the last several decades, leading to the demonstration of several new classes of highly efficient photovoltaic cells. organic, inorganic and hybrid light absorbers such as organic bulk heterojunctions, colloidal quantum-dots and dye-sensitized metal oxide devices have been demonstrated as next generation photovoltaic materials. Among them, hybrid organic-inorganic perovskite materials have attracted substantial attention as photovoltaic light absorbers due to their outstanding electrical and optical properties. Since the processing for obtaining compact and uniform perovskite photoactive layer has intensively studied last few years to achieve high PCEs in solar cells, recent PCEs of perovskite solar cells(PeSCs) have exceeded 23% which is approaching those of commercialized PVs. These achievements have been marked by a constant improvement of deposition techniques by understanding of the crystallization processes. In this perspective, here, we demonstrate several deposition techniques which has a great influence on the crystallization kinetics. First, p-i-n structure PeSCs by optimizing the morphology of perovskite films via solvent mixtures in which all layers are deposited with solution processing at low temperature. we employ a simple device configuration of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS)/CH3NH3PbI3 perovskite/PCBM/aluminum (Al). Improved morphology is obtained in the perovskite film deposited from mixed solvents, leading to improved exciton dissociation efficiency and reduced recombination losses at the interface between perovskite and PCBM and improvements in device efficiency to over 6%. Second, we employed cesium-doped methylammonium lead iodide perovskites (CsXMA1-XPbI3) photoactive layer to improve the performance of planar heterojunction PeSCs. The CsXMA1-XPbI3 perovskite with optimized 10% Cs doping concentration remarkably improves device efficiency from 5.51% to 7.68% due to increases in short-circuit current density and open-circuit voltage by improving light absorption at optimum device thickness and morphology of perovskite film, and widening the energy difference between energy difference between the valence band of the perovskite and low unoccupied molecular orbital level of PCBM Third suggestion is a bridged ternary halide approach to process materials with the formula MAPbI3-y-xBryClx which yields high PCEs in planar, p-i-n type heterojunction PeSCs. This ternary halide perovskite system improves device performance from 12% to 16% when an optimal concentration of 10% Br is incorporated into the binary Cl ??? I systems, via increases in short-circuit current density (JSC), open-circuit voltage(VOC) and fill factor(FF) which arise from the formation of homogeneous crystal domains and a subtle widening of the optical band gap. Remarkably, the ternary halide perovskite devices exhibited approximately 100% internal quantum efficiency (IQE) throughout their entire absorption range (400~800 nm). Furthermore, high quality crystal growth of perovskite layer is critical point to enhance device performance. An easy and effective new process for high efficiency p-i-n planar heterojunction structure of PeSCs by handling the compact seed perovskite layer (CSPL). The CSPL assists vertical growth of perovskite crystal and obtains the high crystalline perovksite photoactive layer which leads to the reduction in the charge transfer resistance and longer photoluminescence lifetime. PeSC device with CSPL shows the remarkably improved PCEs from 15.07% to 19.25% with VOC of 1.16 V in p-i-n structure with pure crystal perovskite and negligible current density-voltage hysteresis. And 20.37% was achieved with CSPL assisted n-i-p structure PeSCs Finally, Lightweight and flexible photovoltaic devices have attracted great interest for specific potential applications, such as miniaturized drones, blimps, and aerospace electronics. This study aims to demonstrate ultralight and flexible perovskite solar cells (PSCs) with orthogonal silver nanowire (AgNW) transparent electrodes fabricated on 1.3-??m-thick polyethylene naphthalate foils. The smooth surface morphologies of the orthogonal AgNW transparent electrodes help prevent nonconducting silver halide formation generated by chemical reaction between the AgNWs and iodine in the active layer. The resultant PSCs with orthogonal AgNW transparent electrodes exhibit substantially improved device performance, achieving a power conversion efficiency (PCE) of 15.18%, over PSCs with random AgNW network electrodes (10.3% PCE). Moreover, ultralight and flexible PSCs with the orthogonal AgNW electrodes exhibit an excellent power-per-weight of 29.4 W??g???1, which is the highest value reported for a lightweight solar cell device. These lightweight energy harvesting platforms can be further expanded for various wearable optoelectronic devices.ope

Confidence in Government and Personal Networks

This Study empirically examines the core assumption of social capital argument that general trust promotes inter-group relation. More specifically, The study attempts to show how the trust in political institutions, which has been assumed to have close relationship with general trust, affects range and composition of personal network. Based on nationally representative data collected by ISDPR (Institute for Social development and Policy Research), this study shows that confidence in government increases the range of personal networks in terms of regional background. In addition, confidence in government also affects the composition of personal networks. The discussion focuses on the relationship between the instrumental value of social relationships and performance of the government. Although the mechanism varies across the characteristics of social parameter, this study concludes that the confidence in government increases the inter-group relationships

Spiro-derivatives as hole transporting materials for improving the performance of perovskite solar cells

The Sun is the most powerful source of energy in the Earth's solar system, which, in part, can be exploited by all the inhabitants of the Earth. The optimal exploitation of the fraction that arrives on earth is, undoubtedly, among the most important challenges nowadays of science. To convert sun light into chemical energy, the first silicon-based device Photovoltaic (PV) solar cells, prepared by Chapin in 1954 exhibiting an efficiency around 6% [1,2] used different semiconducting materials (inorganic, organic, molecular, polymeric, hybrids, quantum dots, etc.). Today the most promising technology to replace/complement crystalline silicon PV [3] are the Perovskites solar cells (PSCs) that emerged since 2009, achieving efficiencies of ~26 %. These results were obtained using commercially available spiro-OMeTAD as hole-transporting material (HTM) that are expensive materials due to its difficult purification and multi-step synthetic protocols (in harsh conditions) which limits its future use in large-scale applications. Considering the negative aspects related to the industrial production of the spiro-OMeTAD, we synthesized some intermediates necessary for the subsequent synthesis of four spiro-derivatives. Excellent results were obtained with some derivatives based on electron-rich spiranic scaffolds [4], synthesized by the Buchwald-Hartwig reaction, carried out in toluene. In this way it was possible to obtain the spiro-PTZ functionalized, by making structural modifications to the previously obtained derivatives, the yield of this synthesis was around 21%. The compounds obtained were incorporated into perovskite solar cells providing efficiencies higher than the standard used (spiroOMeTAD). The devices have been tested under illumination and have shown good stability over time

High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices

Fast vaporizing anti-solvent for high crystalline perovskite to achieve high performance perovskite solar cells

We have deeply studied vaporized anti-solvents effects on the perovskite solar cell performance. Various non polar anti-solvents were tested to achieve the high quality perovskite film. Depending on the boiling point of the anti-solvent, the surface morphology is dramatically changed. In case of high boiling point anti-solvent, 1,2-dichlorobenzene (180.5 degrees C) remains on the perovskite surface even after thermal annealing at 100 degrees C for 10 min. However, the low boiling point chloroform (61.2 degrees C) anti-solvent makes smooth surface morphology of the perovskite film which leads the high performance of perovskite solar cells. This report introduces the vaporization of the anti-solvent affect the surface morphology that needs careful optimization for high performance perovskite solar cells

Cesium-doped methylammonium lead iodide perovskite light absorber for hybrid solar cells

We demonstrate cesium-doping in methylammonium lead iodide perovskites (CsxMA1-xPbI3) light absorbers to improve the performance of inverted-type perovskite/fullerene planar heterojunction hybrid solar cells. CsxMA1-xPbI3 perovskite devices with an optimized 10% Cs doping concentration exhibit remarkable improvement in device efficiency from 5.51% to 7.68% due to increases in short-circuit current density and open-circuit voltage via increased light absorption at optimum device thickness, improved film morphology and a widening of the energy difference between the valence band of the perovskite and lowest unoccupied molecular orbital level of PCBM.close0

Mixed solvents for the optimization of morphology in solution-processed, inverted-type perovskite/fullerene hybrid solar cells

We investigate mixed solvents of N,N-dimethylformamide (DMF) and ??-butyrolactone (GBL) to produce the smooth surface of a perovskite film and uniform crystal domains. This ideal morphology from mixed solvents enhances the power conversion efficiency to over 6% by improving the exciton dissociation efficiency and reducing the recombination loss at both interfaces of PEDOT:PSS/perovskite and perovskite/PCBM.close28

The optimization of intermediate semi-bonding structure using solvent vapor annealing for high performance p-i-n structure perovskite solar cells

The high quality perovskite film construction is the most crucial factor for the high performance perovskite solar cells. Solvent vaopr annelaing (SVA) is one of the best method to achieve the high quality perovkite film. We have fully compared the various high boiling point aprotic solvents N,N-dimethylformamide (DMF), Dimethyl sulfoxide (DMSO) and 1-Methyl-2-pyrrolidone (NMP) for SVA effect for perovskite solar cells. By optimizing temperature and time of SVA, vertically growthed high quality perovskite film via intermediate phase of PbI2-NMP structure was achieved which induces high performance of device. PbI2-NMP intermediate phase of perovskite film can be attributed to pinhole-free, longer carrier lifetime, and oxygen state free. The optimized device with NMP SVA treatment achieved 15.71% of PCE compared to without SVA treatment 7.85% of PCE

Interfacial engineering from material to solvent : A mechanistic understanding on stabilizing alpha-formamidinium lead triiodide perovskite photovoltaics

Formamidinium lead triiodide (FAPbI3) has recently been considered as the most promising candidate to achieve highly efficient perovskite solar cells (PSCs). Excitingly, the state-of-the-art highest efficiency of FAPbI3 based PSCs have reached over 25%. However, their device stability still lags behind other compositions of mixed-cation and mixed-halide perovskites. Interfacial engineering is a very powerful method to address this issue and passivation agents have been intensively developed, however there is a lack of in-depth understanding regarding the solvent selection during post-treatment. Here, we employed cyclohexylmethylammonium iodide (CMAI) as passivation agent, which is investigated using either isopropanol (IPA) or chloroform (CF) as carrier mediator to study the solvent influence on the stabilization of FAPbI3. We observed a suppressed-defect perovskite surface toward distinguished composition with 2D CMA2PbI4 domain and CMAI domain induced by IPA and CF, respectively. Remarkably, post-treatment with solution of CMAI in CF creates a strain-free environment on the perovskite surface, leading to an improved efficiency of approaching 24% and concurrently an extraordinarily stable alpha-phase FAPbI3 PSCs under operation condition, retaining 95% of its initial efficiency after 1050-hour aging. Our resulting device stability is one of the most stable FAPbI3 based PSCs reported in literature

Size tailoring of aqueous germanium nanoparticle dispersions

We demonstrate a practical route to synthesize Ge nanoparticles (NPs) in multi-gram quantities via the laser pyrolysis of GeH4 gas. The size of the as-produced Ge NPs can be precisely controlled in the range of 19.0 to 65.9 nm via a subsequent etching procedure using a dilute H2O 2 solution. Stable water dispersions of Ge NPs yield particles with a Ge/GeO2 core-shell structure, however, the oxide shell can easily be removed and passivated by treatment with HCl. The feed materials used in this process are readily available and lead to non-toxic, water-based dispersions of Ge NPs. The scalability and convenience of this procedure make it attractive as a method to obtain Ge NP dispersions for use in applications such as optoelectronic devices and biosensors.close2