Yaxiong Guo

MgO Nanoparticle Modified Anode for Highly Efficient SnO2-Based Planar Perovskite Solar Cells

Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO‐modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron–hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn‐doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole‐blocking layer exhibits a remarkable improvement of all J–V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification.

Single phase, high hole mobility Cu2O films as an efficient and robust hole transporting layer for organic solar cells

Inorganic hole transport materials (HTMs) are being extensively studied as they are promising for efficient and stable organic solar cells (OSCs) and organic–inorganic hybrid perovskite solar cells. High mobility, earth-abundant, environmentally stable and nontoxic HTMs are the focus of research. This work demonstrates that highly transparent, high mobility and phase pure Cu2O nano-crystal films are promising HTMs for efficient OSC applications. The Cu2O films are synthesized by reactive magnetron sputtering at room temperature. The highest power conversion efficiency of OSCs based on the classical PTB7:PC71BM active layer reaches 8.61% with the Cu2O HTM, which is 15% higher than that of the OSCs with the standard PEDOT:PSS HTM layer. Our study shows that the device based on the Cu2O HTM exhibited better energy level alignment, reduced series resistance and therefore improved charge extraction compared with those based on CuO and PEDOT:PSS HTM layers. The improved photovoltaic performance suggests that Cu2O is a promising HTM for future low temperature roll to roll organic solar cell and even perovskite solar cell fabrication.

Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe2 nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe2 in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe2 has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe2 delivers a high specific capacitance of 759.5 F g-1 at 1 mA cm-2 , which is much larger than that of CoO nanocones (319.5 F g-1 ). In addition, the CoSe2 electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2 . An asymmetric supercapacitor using the CoSe2 as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg-1 at a power density of 1914.7 W kg-1 , and maintains 24.9 Wh kg-1 when power density increased to 7354.8 W kg-1 . Moreover, the CoSe2 electrode also exhibits better oxygen evolution reaction activity than that of CoO.

An integrated organic–inorganic hole transport layer for efficient and stable perovskite solar cells

Certified power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased to an impressive value of 22.1%. The most efficient perovskite solar cells have the n–i–p device architecture and use 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as the hole transport material (HTM). However, there exists microscopic inhomogeneity that is detrimental to the long-term performance of the solar cells, primarily as a result of the hygroscopicity of the lithium bis((trifluomethyl)sulfonyl)amide (LiTFSI) dopant. Here, we report a strategy for reducing heterogeneity by using an organic–inorganic integrated hole transport layer (HTL) composed of the solution-processable conjugated polymer FBT-Th4 and copper oxide (CuxO). The optimized PSCs show significant performance enhancement with power conversion efficiency up to 18.85% from a reverse voltage scan and a stabilized champion efficiency of 18.24% with negligible hysteresis. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells under a high humidity of 70–80% in air.

Improved performance in Ag2S/P3HT hybrid solar cells with a solution processed SnO2 electron transport layer

We successfully constructed a heterojunction structure composed of Ag2S nanocrystals/P3HT conjugated polymer with a relatively high absorption coefficient and broader absorption from the ultraviolet to near-infrared region. The assembled P3HT:Ag2S devices exhibited outstanding short-circuit current density around 19 mA cm−2. Meanwhile, we demonstrated that a low-temperature solution-processed nanocrystalline SnO2 thin film prepared by a facile synthesis method can be an excellent electron transport layer (ETL) material for hybrid solar cells. The SnO2 based hybrid solar cells exhibit an open circuit voltage of 280 mV, which was 100 mV higher than those for devices without SnO2. Based on the above work, we hypothesized that the higher power conversion efficiency is due to the excellent properties of nanocrystalline SnO2 films, such as high electron mobility and excellent transparency at visible wavelength and enhanced exciton dissociation efficiency, and better energy level alignment between FTO and Ag2S for greater photovoltage retention. The simple low temperature low energy consumption, and low-cost soft-chemical process is compatible with the roll-to-roll manufacturing of low-cost hybrid solar cells on flexible substrates.

Organic solar cells based on a Cu2O/FBT-TH4 anode buffer layer with enhanced power conversion efficiency and ambient stability

An organic–inorganic integrated hole transport layer (HTL) composed of a semicrystalline 5,6-difluorobenzothiadiazole based conjugated polymer FBT-TH4 and cuprous oxide (Cu2O) is successfully incorporated into conventional structured organic solar cells (OSCs). The optimized OSCs show a high power conversion efficiency of up to 9.56% and good stability under ambient conditions. The results highlight the potential application of this organic–inorganic integrated HTL in OSCs.

Enhanced performance of perovskite solar cells via anti-solvent nonfullerene Lewis base IT-4F induced trap-passivation

The defects at the surfaces and grain boundaries of organic–inorganic halide perovskite films are detrimental to both the efficiency and stability of perovskite solar cells. Here, we introduce an in situ method with a new nonfullerene small molecule (IT-4F) that can effectively passivate ionic defects of hybrid perovskites with their positively charged components, under-coordinated Pb2+, during the anti-solvent process of perovskite film formation. This efficient defect passivation reduces the charge trap density and increases the carrier recombination lifetime. Furthermore, it reduces the open-circuit-voltage deficit of the p–i–n-structured device, and boosts the efficiency to a value of 18.3%. Moreover, the defect healing also significantly enhances the stability of films under ambient conditions. Our findings provide an avenue for defect passivation to further improve both the efficiency and stability of perovskite solar cells.

A simple synthesis of transparent and highly conducting p-type CuxAl1−xSy nanocomposite thin films as the hole transporting layer for organic solar cells

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (CuxAl1−xSy) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated CuxAl1−xSy films were deposited at 60 °C using an aqueous solution of copper(II) chloride dihydrate (CuCl2·2H2O), aluminium nitrate nonohydrate [Al(NO3)3·9H2O], thiourea [(NH2)2CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the CuxAl1−xSy films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm2 V−1 s−1 and the best conductivity obtained was 546 S cm−1. The CuxAl1−xSy films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the CuxAl1−xSy films as the HTL. These results demonstrate the remarkable potential of CuxAl1−xSy as hole transport material for opto-electronic devices.