Current Advancements in Material Research and Techniques Focusing on Lead-free Perovskite Solar Cells

Organic-inorganic lead halide perovskite solar cells (PSCs) recently achieved a photo-to-electricity conversion efficiency (PCE) of 22.1%. They drew much attention as promising photovoltaic devices. However, the Pb-based PSCs face great challenges for commercial and industrial applications due to the instability and the toxicity of perovskite materials. Herein, we summarize the current development of various types of Pb-free perovskites, such as the Sn-, Bi-, Ge-, Sr-, and Cu-based perovskites and their devices. In addition, we will address some remaining issues and prospects of the Pb-free PSCs

First-principles study of electronic and optical properties of lead-free double perovskites Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I)

Organolead halide perovskite is regarded as the most promising light-harvesting material for next-generation solar cells; however, the intrinsic instability and toxicity of lead are still of great concern. Bismuth is ecofriendly and has electronic properties similar to those of lead, which has gradually attracted interest for optoelectronic applications. However, the valence state of bismuth is different from that of lead, eliminating the possibility of replacing lead by bismuth in organolead halide perovskites. To address this matter, one feasible strategy is to construct B-site double perovskites by the combination of Bi3+ and B+ in 1:1 ratio. In this work, lead-free halide double perovskites of the form Cs2NaBX6 (B = Sb, Bi; X = Cl, Br, I) were investigated by first-principles calculations. The electronic properties, optical absorption coefficients, and thermodynamic stability of these compounds were investigated to ascertain their potential application in solar energy conversion. The results provide theoretical support for the exploration of lead-free perovskite materials in potential optoelectronic applications

In-situ growth of nanowire WO2.72 on carbon cloth as a binder-free electrode for flexible asymmetric supercapacitors with high performance

For the first time, WO2.72 nanowires were in-situ grown on carbon cloth by a simple solvothermal reaction. The nanowire WO2.72/carbon cloth (NW WO2.72/CC) electrode showed good electrochemical performance with specific capacitance (C s) reaching up to 398 F g-1 at a current density of 2 A g-1. The capacitance of 240 F g-1 was retained at a high current density of 16 A g-1. To further evaluate the energy storage performance, flexible asymmetric supercapacitors (FASCs) were fabricated using the activated carbon/carbon cloth (AC/CC) as negative electrode and NW WO2.72/CC as positive electrode, respectively. The FASCs delivered a high energy density of 28 Wh kg-1 at a power density of 745 W kg-1 and 13 Wh kg-1 even at a high power density of 22.5 kW kg-1. More impressively, 81% of the specific capacitance of the FASCs was retained after 10,000 cycles, indicating excellent cycle stability. This work indicates the NW WO2.72/CC holds a great potential for application in energy storage devices

Minute quantities of hexagonal nanoplates PtFe alloy with facile operating conditions enhanced electrocatalytic activity and durability for oxygen reduction reaction

Pt-based alloys have been explored as the most promising cathode catalyst for fuel cells due to their excellent electrocatalytic activity in oxygen reduction reaction (ORR). However, the long-term performance of Pt-based alloys is compromised owing to the de-alloying behavior under the corrosive circumstance. More importantly, the complicated synthesized methods have hindered their further practical application. In this report, a facile and effective operating conditions-assisted method has been developed to synthesize the stable hexagonal nanoplates PtFe alloy with a high electrocatalytic activity. In the three prepared PtM (M: Fe, Co, Ni) alloy samples, the PtFe alloy exhibits a superior catalytic activity, which improves by about 100 and 178?mV for half-wave potential in alkaline and acidic medium with the same Pt-loading amount, respectively. In addition, the PtFe alloy catalyst exhibits an electrochemical stability, compared to the conventional carbon-supported Pt catalysts. In view of the advantages of the facile operating preparation and the excellent electrocatalytic performance, we believe that the hexagonal nanoplates PtFe alloy holds great application as a promising electrocatalyst in polymer electrolyte membrane fuel cell (PEMFC)

A review on electrochemical synthesized copper-based catalysts for electrochemical reduction of CO2 to C2+ products

In recent decades, catalytic reduction of CO2 is a hot topic in the research field of electrocatalysis. Copper is the only metal catalyst capable of producing multiple carbon (C2+) products in electrocatalytic CO2 reduction (ECR), however, there are still many challenges such as low selectivity, serious hydrogen evolution (HER) and poor stability. So far, various synthesis methods have been developed for Cu-based catalysts. Compared with ordinary chemical synthesis, electrochemical method has the advantages of simple process, controllable conditions, good safety and eco-friendly. In this review, the recent progress in synthesizing different types of Cu-based catalysts by means of the electrochemical method are comprehensively reviewed. The engineering strategies and the effects of the key preparation conditions on the catalytic performance of CO2 electroreduction for C2+ products are discussed in details. Besides, copper-based catalysts synthesized by electrochemical methods combined with the ordinary methods (wet chemical methods, plasma activated methods and other methods) were also outlined. Finally, the development potential of electrochemical synthesis for Cu-based catalysts are recommended, which provides a direction for the future development of Cu-based catalysts with low cost and high ECR performance

Transparent Conductive Oxide Layer and Hole Selective Layer Free Back-Contacted Hybrid Perovskite Solar Cell

Back-contacted architectures have been under intensive investigation for that transparent conductive oxide (TCO) less solar cells (SCs) can be easily realized which avoid the transmission loss of light caused by TCO, typically comprised in conventional solar cells. Here, network-like porous Ti was first utilized as the back-contacted electrode, and a new design allows for a novel back-contacted hybrid perovskite SC without TCO and hole selective layer, which shows a power output of 3.88% with long-term stability. In addition, it avoids limit available collection area of electrodes in the recent reported interdigitated electrode (IDE) based back-contacted TCO-less SCs

Metal-organic framework derived hierarchical porous TiO2 nanopills as a super stable anode for Na-ion batteries

Hierarchical porous TiO2 nanopills were synthesized using a titanium metal-organic framework MIL-125(Ti) as precursor. The as-synthesized TiO2 nanopills owned a large specific surface area of 102 m2/g and unique porous structure. Furthermore, the obtained TiO2 nanopills were applied as anode materials for Na-ion batteries for the first time. The as-synthesized TiO2 nanopills achieved a high discharge capacity of 196.4 mAh/g at a current density of 0.1 A/g. A discharge capacity of 115.9 mAh/g was obtained at a high current density of 0.5 A/g and the capacity retention was remained as high as 90% even after 3000 cycles. The excellent electrochemical performance can be attributed to its unique hierarchical porous feature

Preparation of Perovskite Films under Liquid Nitrogen Atmosphere for High Efficiency Perovskite Solar Cells

High quality perovskite film with high coverage and tight grain arrangement is critical for achieving high-efficiency and high-stability perovskite solar cells (PSCs). In this work, high quality perovskite films were successfully prepared by liquid nitrogen assisted method (LN method). Here, the vaporization of liquid nitrogen reduces the ambient temperature and absorb thermal energy from the substrate surface to accelerate the nucleation of perovskite. The results of scanning electron microscopy (SEM) shows that the perovskite films prepared by liquid nitrogen assisted method were dense and pinhole-free. The devices prepared by the LN method leads to a high-efficiency upto 16.53%, and the high efficiency device could maintain over 89% of the initial power conversion efficiency (PCE) even after 30 days storage in a desiccator at room temperature

Tandem Dye-Sensitized Solar Cells Based on TCO-less Back Contact Bottom Electrodes

Mechanically stacked and series connected tandem dye sensitized solar cells (T-DSSCs) are fabricated in novel architectures. The architecture consist of TCO tandem DSSCs stacked with TCO-less back contact DSSCs as bottom electrodes (TCO-less tandem DSSCs). Resulting TCO-less tandem DSSCs architecture finds its usefulness in efficient photon harvesting due to improved light transmission and enhanced photons reaching to the bottom electrodes. The fabricated tandem performance was verified with visible light harvesting model dyes D131 and N719 as a proof of concept and provided the photoconversion efficiency (PCE) of 6.06% under simulated condition. Introduction of panchromatic photon harvesting by utilizing near infrared light absorbing Si-phthalocyanine dye in combination with the modified tandem DSSC architecture led to enhancement in the PCE up to 7.19%.India-Japan Expert Group Meeting on Biomolecular Electronics & Organic Nanotechnology for Environment Preservation (IJEGMBE 2015), December 23-26, 2015, Fukuoka, Japa

Theoretical study of the influence of doped oxygen group elements on the properties of organic semiconductors

Organic semiconductor materials are widely used in the field of organic electronic devices due to their wide variety, low price, and light weight. However, their developments are still restrained by their low stability and carrier mobility. Density functional theory (DFT) was used to study the influence of doped oxygen group elements (O, S, Se, and Te) on the properties of organic semiconductor materials (seven-membered benzothiophene, o-pentacene, thiophene derivatives, and pentacene) in this paper. Based on the calculation of EHOMO, ELUMO, ΔE, and total energy, the performances of organic semiconductor materials without and with doped elements were compared, and it was found that the doping of multi-element Te makes the material have high stability and potential high mobility. For these studied organic semiconductor materials, when the atoms of the doped site change in the order of O, S, Se, and Te, the carrier mobility gradually increases, and the molecules show a tendency of stability. In this paper, promising doping elements and doping methods for these studied molecules are determined through calculations and screening out suitable materials more efficiently and economically without a large amount of repetitive experimental work, which may provide a theoretical basis and guidance for preparing high-performance organic semiconductor materials