Xiaokun Yang

Flexible and Semitransparent Organolead Triiodide Perovskite Network Photodetector Arrays with High Stability.

Organolead triiodide perovskite (CH3NH3PbI3) as a light-sensitive material has attracted extensive attention in optoelectronics. The reported perovskite photodetectors (PDs) mainly focus on the individual, which limits their spatial imaging applications. Uniform perovskite networks combining transparency and device performance were synthesized on poly(ethylene terephthalate) (PET) by controlling perovskite crystallization. Photodetector arrays based on above network were fabricated to demonstrate the potential for image mapping. The trade-off between the PD performance and transparency was systematically investigated and the optimal device was obtained from 30 wt % precursor concentration. The switching ratio, normalized detectivity, and equivalent dark current derived shot noise as the critical parameters of PD arrays reached 300, 1.02 × 10(12) Jones, and 4.73 × 10(-15)A Hz(-1/2), respectively. Furthermore, the PD arrays could clearly detect spatial light intensity distribution, thus demonstrating its preliminary imaging function. The perovskite network PD arrays fabricated on PET substrates could also conduct superior flexibility under wide angle and large number of bending. For the common problem of perovskite optoelectronics in stability, the perovskite networks sheathed with hydrophobic polymers greatly enhanced the device stability due to the improved interface contacts, surface passivation, and moisture isolation. Taking into consideration transparency, flexibility, imaging and stability, the present PD arrays were expected to be widely applied in visualized portable optoelectronic system.

High Quantum Yield Blue Emission from Lead-Free Inorganic Antimony Halide Perovskite Colloidal Quantum Dots

Colloidal quantum dots (QDs) of lead halide perovskite have recently received great attention owing to their remarkable performances in optoelectronic applications. However, their wide applications are hindered from toxic lead element, which is not environment- and consumer-friendly. Herein, we utilized heterovalent substitution of divalent lead (Pb2+) with trivalent antimony (Sb3+) to synthesize stable and brightly luminescent Cs3Sb2Br9 QDs. The lead-free, full-inorganic QDs were fabricated by a modified ligand-assisted reprecipitation strategy. A photoluminescence quantum yield (PLQY) was determined to be 46% at 410 nm, which was superior to that of other reported halide perovskite QDs. The PL enhancement mechanism was unraveled by surface composition derived quantum-well band structure and their large exciton binding energy. The Br-rich surface and the observed 530 meV exciton binding energy were proposed to guarantee the efficient radiative recombination. In addition, we can also tune the inorganic perovskite QD (Cs3Sb2X9) emission wavelength from 370 to 560 nm via anion exchange reactions. The developed full-inorganic lead-free Sb-perovskite QDs with high PLQY and stable emission promise great potential for efficient emission candidates.

2D Lead Dihalides for High-Performance Ultraviolet Photodetectors and their Detection Mechanism Investigation

2D halide semiconductors, a new family of 2D materials in addition to transition metal dichalcogenides, present ultralow dark current and high light conversion yield, which hold great potential in photoconductive detectors. Herein, a facile aqueous solution method is developed for the preparation of large-scale 2D lead dihalide nanosheets (PbF2-x Ix ). High-performance UV photodetectors are successfully implemented based on 2D PbF2-x Ix nanosheets. By modulating the components of halogens, the bandgap of PbF2-x Ix nanosheets can be tuned to meet varied detection spectra. The photoresponse dependence on incident power density, wavelength, detection environment, and temperature are systematically studied to investigate their detection mechanism. For PbI2 photodetectors, they are dominantly driven by a photoconduction mechanism and show a fast response speed and a low noise current density. A high normalized detectivity of 1.5 × 1012 Jones and an ION /IOFF ratio up to 103 are reached. On the other hand, PbFI photodetectors demonstrate a photogating mechanism mediated by trap states showing high responsivity. The novel 2D halide materials with wide bandgaps, superior detection performance, and facile synthesis process can enrich the Van der Waals solids family and hold great potential for a wide variety of applications in advanced optoelectronics.

Improving the Performance of PbS Quantum Dot Solar Cells by Optimizing ZnO Window Layer

AbstractComparing with hot researches in absorber layer, window layer has attracted less attention in PbS quantum dot solar cells (QD SCs). Actually, the window layer plays a key role in exciton separation, charge drifting, and so on. Herein, ZnO window layer was systematically investigated for its roles in QD SCs performance. The physical mechanism of improved performance was also explored. It was found that the optimized ZnO films with appropriate thickness and doping concentration can balance the optical and electrical properties, and its energy band align well with the absorber layer for efficient charge extraction. Further characterizations demonstrated that the window layer optimization can help to reduce the surface defects, improve the heterojunction quality, as well as extend the depletion width. Compared with the control devices, the optimized devices have obtained an efficiency of 6.7% with an enhanced Voc of 18%, Jsc of 21%, FF of 10%, and power conversion efficiency of 58%. The present work suggests a useful strategy to improve the device performance by optimizing the window layer besides the absorber layer.

Low-temperature-processed SnO2–Cl for efficient PbS quantum-dot solar cells via defect passivation

Colloidal quantum dots (CQDs) exhibit extraordinary features due to their bandgap tunability and solution processing. Instead of the ZnO layer usually used as the electron transport layer (ETL) in CQD heterojunction devices, we developed, for the first time, tin dioxide (SnO2) as the ETL in colloidal quantum dot solar cells (QDSCs). Its wider bandgap and higher electron mobility, as well as appropriate band alignment with PbS QDs, could favor light absorption and photocarrier extraction. Our low-temperature processed SnO2 film could retain chlorine atoms (SnO2–Cl) to achieve interface passivation in QDSCs. Utilizing 1-ethyl-3-methylimidazolium iodide (EMII) as the absorber ligand, our superior device obtained a power conversion efficiency of 9.37%, which was 44% higher than that of a control device. Physical characterizations revealed that this remarkable improvement could be ascribed to the chlorine passivation of the SnO2/QD interface contact and to the EMII ligand passivation effect on the QD surface. Our newly developed ETL, along with an efficient interface passivation technique, is expected to enhance the performance of full solution-processed colloidal QDSCs.

Efficient interface and bulk passivation of PbS quantum dot infrared photodetectors by PbI2 incorporation

Lead sulfide colloidal quantum dots (PbS CQDs) exhibit outstanding optoelectronic properties owing to their low temperature solution-processability and bandgap tunability. PbS QD heterojunction detectors suffer from an incomplete interface and bulk passivation. Herein, a simple passivation method based on PbI2 was developed, which can effectively suppress the heterojunction interface and PbS QD surface defects by interface and ligand passivation. Utilizing the present strategies, PbS QD photodetectors can decrease the dark current and simultaneously increase the photocurrent. Such photodiode detectors also showed a fast response on the order of microseconds which is much faster than that of photoconductive CQD detectors (millisecond order). Also, an ultra-high specific detectivity of 1013 Jones was obtained. Meanwhile, the energy conversion efficiency of PbI2 based devices reached 8%, a twofold value compared to the control one. The convenient and efficient passivation method is expected to hold great potential for high performance QD optoelectronic devices.