No abstract

The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in by up to 100 millivolts. We achieved a high of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

We present MMDetection, an object detection toolbox that contains a rich set of object detection and instance segmentation methods as well as related components and modules. The toolbox started from a codebase of MMDet team who won the detection track of COCO Challenge 2018. It gradually evolves into a unified platform that covers many popular detection methods and contemporary modules. It not only includes training and inference codes, but also provides weights for more than 200 network models. We believe this toolbox is by far the most complete detection toolbox. In this paper, we introduce the various features of this toolbox. In addition, we also conduct a benchmarking study on different methods, components, and their hyper-parameters. We wish that the toolbox and benchmark could serve the growing research community by providing a flexible toolkit to reimplement existing methods and develop their own new detectors. Code and models are available at https: //github.com/open-mmlab/mmdetection. The project is under active development and we will keep this document updated.

Photovoltaic solar cells based on metal halide perovskites have gained considerable attention over the past decade because of their potentially low production cost, earth-abundant raw materials, ease of fabrication and ever-increasing power conversion efficiencies of up to 25.2%. This type of solar cells offers the promise of generating electricity at a more competitive unit price than traditional fossil fuels by 2035.Nevertheless, the best research cell efficiencies are still below the theoretical limit defined by the Shockley-Queissier theory owing to the presence of non-radiative recombination losses. In this Review, we analyse the predominant pathways that contribute to nonradiative recombination losses in perovskite solar cells, and evaluate their impact on device performance. We then discuss how non-radiative recombination losses can be estimated through reliable characterization techniques, and highlight some notable advances in mitigating these losses, which hint at pathways towards defect-free perovskite solar cells.

Visibly transparent photovoltaic devices can open photovoltaic applications in many areas, such as building-integrated photovoltaics or integrated photovoltaic chargers for portable electronics. We demonstrate high-performance, visibly transparent polymer solar cells fabricated via solution processing. The photoactive layer of these visibly transparent polymer solar cells harvests solar energy from the near-infrared region while being less sensitive to visible photons. The top transparent electrode employs a highly transparent silver nanowire-metal oxide composite conducting film, which is coated through mild solution processes. With this combination, we have achieved 4% power-conversion efficiency for solution-processed and visibly transparent polymer solar cells. The optimized devices have a maximum transparency of 66% at 550 nm.

During the past 6 years, perovskite solar cells have experienced a rapid development and shown great potential as the next‐generation photovoltaics. For the perovskite solar cells with regular structure (n‐i‐p structure), device efficiency has reached over 20% after the intense efforts of researchers from all over the world. Recently, perovskite solar cells with the inverted structure (p‐i‐n structure) have been becoming more and more attractive, owing to their easy‐fabrication, cost‐effectiveness, and suppressed hysteresis characteristics. Some recent progress in their device performance and stability has indicated their promising future. Here, recent developments and future perspectives about inverted perovskite solar cells are reviewed. Interface engineering, film morphology control, device stability, hysteresis phenomena and other research hotspots are discussed to present the roadmap for the development of inverted perovskite solar cells.

BROADER CONTEXTPerovskite solar cells, which promise to deliver the highest efficiency, lowest cost nextgeneration PV technology, have been largely advanced over the last few years by improvements in the polycrystalline thin film quality. So far, improvements in film uniformity and smoothness, have mainly been at the expense of crystalline grain-size, and charge recombination losses at defect sites. High luminescence efficiency, which is an indication of better optoelectronic quality, has generally been found in films with polycrystalline grains of many micrometres in scale. This suggests a current compromise between ideal morphology and ideal optoelectronic quality.For traditional semiconductors and crystalline solids, the influence of impurity ion doping has been studied extensively and can either alter the crystallisation or induced electronic positive or negative type doping. However, in the perovskite community, impurity doping has been largely unexplored. Here, we show that doping the perovskite solution with Al 3+ , which has a much smaller ionic radius than Pb 2+ , has profoundly positive influenced on the crystalline and optoelectronic quality of the perovskite absorber layer: We demonstrate a two-fold increase in the photoluminescence quantum efficiency and a significantly reduced electronic disorder, despite the films still having polycrystalline grains on the order of one micrometer is scale. This largely overcomes the trade-off between film smoothness and optoelectronic quality, and these improvements translate into highly efficient planar heterojunction perovskite solar cells.Our work paves the way for further improvement of the optoelectronic quality of perovskite thin films, and subsequent devices, via highlighting a new avenue for investigation of the role of dopant impurities upon crystallisation and controlling the electronic defect density in the perovskite thin films. ABSTRACTRealizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices. One of the main challenges is to eliminate the presence of charge recombination centres throughout the film which have been observed to be most densely located at regions near the grain boundaries.Here, we introduce aluminium acetylacetonate to the perovskite precursor solution, which improves the crystal quality by reducing the microstrain in the polycrystalline film. At the same time, we achieve a reduction in the non-radiative recombination rate, a remarkable improvement in the photoluminescence quantum efficiency (PLQE) and a reduction in the electronic disorder deduced from an Urbach energy of only 12.6 meV in complete devices. As a result, we demonstrate a power-conversion efficiency (PCE) of 19.1% with negligible hysteresis in planar heterojunction solar cells comprising all organic p and n-type charge collection layers. Our work shows that...

Blue luminescent reduced state carbon dots were prepared by reducing carbon dots with NaBH(4). The quantum yield of the reduced state carbon dots increased from 2% to 24% and the maximum emission wavelength shifted from 520 to 450 nm. This offers a simple pathway to enhance the luminescence of carbon dots.