Borui Li

Low-Temperature Solution-Processed Tin Oxide as an Alternative Electron Transporting Layer for Efficient Perovskite Solar Cells

Lead halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO2 as the electron transporting layers (ETLs). Here, we demonstrate that low-temperature solution-processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Our best-performing planar cell using such a SnO2 ETL has achieved an average efficiency of 16.02%, obtained from efficiencies measured from both reverse and forward voltage scans. The outstanding performance of SnO2 ETLs is attributed to the excellent properties of nanocrystalline SnO2 films, such as good antireflection, suitable band edge positions, and high electron mobility. The simple low-temperature process is compatible with the roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates.

Self-powered narrowband p-NiO/n-ZnO nanowire ultraviolet photodetector with interface modification of Al2O3

All inorganic, self-powered, narrowband, and rapid response p-NiO/n-ZnO nanowire (NW) ultraviolet (UV) photodetectors were fabricated and investigated with Al2O3 as an interface modification layer. Al2O3 films grown by atomic layer deposition can greatly suppress the surface defects on ZnO NWs and improve the p-NiO/n-ZnO NW interface. The photo-response of the photodetector in the 430–500 nm wavelength range was greatly inhibited and the full-width at half-maximum of the response spectrum was less than 30 nm. A large responsivity of 1.4 mA/W was achieved under a 380 nm UV irradiation (0.36 mW/cm2) at zero bias and the response time of the device was less than 0.04 s. Such a simple interface modification method might promote the developing of ZnO NW based narrowband photodetectors.

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.

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.

NH4F-assisted one-pot solution synthesis of hexagonal ZnO microdiscs for efficient ultraviolet photodetection

One-pot solution method to grow large hexagonal ZnO microdiscs with the aid of ammonium fluoride (NH4F) mineralizer has been realized. The size, morphology, crystallinity and optical properties of the synthesized ZnO microdiscs can be efficiently modulated by the concentration of NH4F. X-ray diffraction and scanning electron microscopy analyses illustrate that hexagonal ZnO microdiscs achieved at 0.03 M NH4F concentration have larger disc size and narrower full-width value at half maximum of (002) peak. It implies better crystal quality compared with those from other additive concentrations. Photoluminescence results also demonstrate the same trend. These results indicate that with proper addition of NH4F, the crystal quality of ZnO microdiscs has been improved and defects have been suppressed. Furthermore, a UV photodetector has been fabricated by simply transferring the ZnO microdiscs grown with 0.03 M NH4F onto a p-type silicon substrate. The device exhibits photosensitive behaviour at 365 nm UV light illuminating when −0.6 V is applied. The response time as well as recovery time is less than 0.1 s. The relatively large photoresponsivity of 1.19 A W−1 with power consumption less than 10 nW makes it possible in application field of highly efficient low power consumption UV detection.

Indium-doped ZnO horizontal nanorods for high on-current field effect transistors

High on-current field effect transistors (FETs) are highly desirable for driving information displays such as active matrix organic light-emitting diode displays. Herein, indium-doped ZnO (IZO) horizontal nanorod arrays were fabricated for high on-current FETs by a facile and tunable hydrothermal method. We have found that indium doping can influence the growth behavior of ZnO nanorods. After indium doping, the ZnO nanorods tend to grow better along the horizontal direction and have a better flat morphology. More importantly, indium doping increases the carrier concentration of the IZO nanorods; this leads to better transfer and output performances of the IZO nanorod FETs. Therefore, the IZO nanorod FET with a high on-current of 6.39 × 10−4 A and a field effect mobility of 26.3 cm2 V−1 s−1 has been synthesized and demonstrated in this study.