Qi Jiang

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000u2009cdu2009m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

Planar-Structure Perovskite Solar Cells with Efficiency beyond 21%

Low temperature solution processed planar-structure perovskite solar cells gain great attention recently, while their power conversions are still lower than that of high temperature mesoporous counterpart. Previous reports are mainly focused on perovskite morphology control and interface engineering to improve performance. Here, this study systematically investigates the effect of precise stoichiometry, especially the PbI2 contents on device performance including efficiency, hysteresis and stability. This study finds that a moderate residual of PbI2 can deliver stable and high efficiency of solar cells without hysteresis, while too much residual PbI2 will lead to serious hysteresis and poor transit stability. Solar cells with the efficiencies of 21.6% in small size (0.0737 cm2 ) and 20.1% in large size (1 cm2 ) with moderate residual PbI2 in perovskite layer are obtained. The certificated efficiency for small size shows the efficiency of 20.9%, which is the highest efficiency ever recorded in planar-structure perovskite solar cells, showing the planar-structure perovskite solar cells are very promising.

Highly efficient and stable planar heterojunction perovskite solar cells via a low temperature solution process

Both high efficiency and good stability of organometal trihalide perovskite solar cells are of central importance for their practical application. Here we report the fabrication of highly efficient and stable planar heterojunction perovskite solar cells through a simple and low temperature solution process. By combining the slow growth of the perovskite film and the introduction of a ZnO interlayer, a maximum power conversion efficiency of 16.8% was achieved. More importantly, the devices showed excellent stability, which can maintain their almost original performance after storing in ambient air for two months. It has been found that the ZnO interlayer is critical in enhancing the efficiency and stability of the devices. Furthermore, the low temperature solution process and the planar device structure used in this work are well compatible with the large-area and flexible substrates.

Efficient green light-emitting diodes based on quasi-two-dimensional composition and phase engineered perovskite with surface passivation

Perovskite light-emitting diodes (LEDs) are attracting great attention due to their efficient and narrow emission. Quasi-two-dimensional perovskites with Ruddlesden–Popper-type layered structures can enlarge exciton binding energy and confine charge carriers and are considered good candidate materials for efficient LEDs. However, these materials usually contain a mixture of phasesxa0and the phase impurity couldxa0cause low emission efficiency. In addition, converting three-dimensional into quasi-two-dimensional perovskite introduces more defects on the surface or at the grain boundaries due to the reduction of crystal sizes. Both factors limit the emission efficiency of LEDs. Here, firstly, through composition and phase engineering, optimal quasi-two-dimensional perovskites are selected. Secondly, surface passivation is carried out by coating organic small molecule trioctylphosphine oxide on the perovskite thin film surface. Accordingly, green LEDs based on quasi-two-dimensional perovskite reach a current efficiency of 62.4u2009cdu2009A−1 and external quantum efficiency of 14.36%.Solution-processable halide perovskites have high luminous efficiency and excellent chemical tunability, making them ideal candidates for light-emitting diodes. Here Yang et al. achieve high external quantum efficiency of 14% in the devices by fine-tuning the phase and passivating the surface defects.

Solvent-controlled growth of inorganic perovskite films in dry environment for efficient and stable solar cells

Inorganic halide perovskites such as cesium lead halide are promising due to their excellent thermal stability. Cesium lead iodide (CsPbI3) has a bandgap of 1.73u2009eV and is very suitable for making efficient tandem solar cells, either with low-bandgap perovskite or silicon. However, the phase instability of CsPbI3xa0is hindering the further optimization of device performance. Here, we show that high quality and stable α-phase CsPbI3 film is obtained via solvent-controlled growth of the precursor film in a dry environment. A 15.7% power conversion efficiency of CsPbI3 solar cells is achieved, which is the highest efficiency reported for inorganic perovskite solar cells up to now. And more importantly, the devices can tolerate continuous light soaking for more than 500u2009h without efficiency drop.Cesium lead iodide inorganic perovskite solar cells have great potential but the phase instability hinders their development. Here Wang et al. show a controlled drying process to make phase stable and highly efficient solar cells with power conversion efficiency of 15.7%.

A high-performance photodetector based on an inorganic perovskite–ZnO heterostructure

All-inorganic perovskites, such as CsPbX3 (X = Cl, Br, I), have recently emerged as highly promising optoelectronic materials due to their excellent physical properties, especially their higher thermal stability. However, the performance of a CsPbX3-based photodetector is worse than its counterparts based on organic–inorganic hybrid perovskites. In this work, we demonstrate flexible high performance photodetectors based on the CsPbBr3/ZnO heterostructure using solution-processesing. Owing to the interfacial charge transfer from perovskite to ZnO, the photocurrent of devices was enhanced by more than one order of magnitude after the introduction of a ZnO layer. The CsPbBr3/ZnO heterostructure photodetectors exhibited high sensitivity with an on/off ratio of >104 under 450 nm light illumination and a high photoresponsivity of 4.25 A W−1. Furthermore, CsPbBr3/ZnO photodetectors with excellent stability and outstanding flexibility were also demonstrated. This work demonstrates that CsPbBr3/ZnO heterostructures are promising for the construction of high-performance photodetectors and other optoelectronic devices.

SnO2: A Wonderful Electron Transport Layer for Perovskite Solar Cells

The highest power conversion efficiency of perovskite solar cells is beyond 22%. Charge transport layers are found to be critical for device performance and stability. A traditional electron transport layer (ETL), such as TiO2 , is not very efficient for charge extraction at the interface, especially in planar structure. In addition, the devices using TiO2 suffer from serious degradation under ultraviolet illumination. SnO2 owns a better band alignment with the perovskite absorption layer and high electron mobility, which is helpful for electron extraction. In this Review, recent progresses in efficient and stable perovskite solar cells using SnO2 as ETL are summarized.

Interface Engineering of High-Performance Perovskite Photodetectors Based on PVP/SnO2 Electron Transport Layer

Hybrid organic-inorganic perovskites have attracted intensive interest as active materials for high-performance photodetectors. However, studies on the electron transport layer (ETL) and its influence on the response time of photodetectors remain limited. Herein, we compare the performances of perovskite photodetectors with TiO2 and SnO2 ETLs, especially on the response time. Both photodetectors exhibit a high on/off current ratio of 105, a large detectivity around 1012 Jones, and a linear dynamic range over 80 dB. The SnO2-based perovskite photodiodes show ultrahigh response rates of 3 and 6 μs for the rise and decay times, respectively. However, photodetectors with TiO2 ETLs have low responsivity and long response time at low driving voltage, which is attributed to the electron extraction barrier at the TiO2/perovskite interface and the charge traps in the TiO2 layer. Furthermore, the dark current of SnO2-based perovskite photodiodes is effectively suppressed by inserting a poly(vinylpyrrolidone) interlayer, and then the on/off current ratio increases to 1.2 × 106, corresponding to an improvement of 1 order of magnitude. Such low-cost, solution-processable perovskite photodetectors with high performance show promising potential for future optoelectronic applications.