Since the first introduction of the organic–inorganic hybrid perovskite in the field of optoelectronics, extraordinary progress in both the photoelectric-conversion-efficiency and stability of perovskite solar cells (PSCs) have been witnessed. However, a variety of drawbacks associated with defects in PSCs, such as energy deficits, ion migration, operational instability and hysteresis, greatly hinder the potential industrial applications of PSCs. Herein, a systematic and comprehensive understanding of the origin, classification, nature, relationships and overlapping effects of defects in perovskite is summarized and reviewed. According to their positions in the energy structure relative to band edges, shallow- and deep-level defects are summarized, while point defects, undercoordinated ions, impurities and pinholes are categorized based on a dimension-criterion. We look at the established understanding of how the detrimental defects induce non-radiative recombination, charge trapping and scattering, ion migration and hysteresis, providing a relatively clear relationship between the performance and defects in perovskite films. An overview of the defect passivation strategies is presented on the fabrication route, including film formation, post-treatment and interlayer engineering between the perovskite layer and charge transport layer, giving a unique perspective. Based on defect passivation engineering, challenges and suggestions to break the bottlenecks of PSCs on the way to commercialization are proposed.

Defect passivation strategies in perovskites for an enhanced photovoltaic performance

With the help of a quantum simulator and Bayesian inference it is possible to determine the unknown Hamiltonian of a quantum system. An experiment demonstrates this using a photonic quantum simulator and a solid-state system. The efficient characterization of quantum systems1,2,3, the verification of the operations of quantum devices4,5,6 and the validation of underpinning physical models7,8,9, are central challenges for quantum technologies10,11,12 and fundamental physics13,14. The computational cost of such studies could be improved by machine learning enhanced by quantum simulators15,16. Here we interface two different quantum systems through a classical channel—a silicon-photonics quantum simulator and an electron spin in a diamond nitrogen–vacancy centre—and use the former to learn the Hamiltonian of the latter via Bayesian inference. We learn the salient Hamiltonian parameter with an uncertainty of approximately 10−5. Furthermore, an observed saturation in the learning algorithm suggests deficiencies in the underlying Hamiltonian model, which we exploit to further improve the model. We implement an interactive version of the protocol and experimentally show its ability to characterize the operation of the quantum photonic device.

Experimental quantum Hamiltonian learning

Highly Efficient Sn/Pb Binary Perovskite Solar Cell via Precursor Engineering: A Two-Step Fabrication Process

A high-quality perovskite photoactive layer plays a crucial role in determining the device performance. An additive engineering strategy is introduced by utilizing different concentrations of N,1-diiodoformamidine (DIFA) in the perovskite precursor solution to essentially achieve high-quality monolayer-like perovskite films with enhanced crystallinity, hydrophobic property, smooth surface, and grain size up to nearly 3 µm, leading to significantly reduced grain boundaries, trap densities, and thus diminished hysteresis in the resultant perovskite solar cells (PSCs). The optimized devices with 2% DIFA additive show the best device performance with a significantly enhanced power conversion efficiency (PCE) of 21.22%, as compared to the control devices with the highest PCE of 19.07%. 2% DIFA modified devices show better stability than the control ones. Overall, the introduction of DIFA additive is demonstrated to be a facile approach to obtain high-efficiency, hysteresis-less, and simultaneously stable PSCs.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201901241

Additive Engineering to Grow Micron-Sized Grains for Stable High Efficiency Perovskite Solar Cells

Growing large, oriented grains of perovskite often leads to efficient devices, but it is unclear if properties of the grains are responsible for the efficiency. Domains observed in SEM are commonly misidentified with crystallographic grains, but SEM images do not provide diffraction information. We study methylammoinium lead iodide (MAPbI3) films fabricated via flash infrared annealing (FIRA) and the conventional antisolvent (AS) method by measuring grain size and orientation using electron back-scattered diffraction (EBSD) and studying how these affect optoelectronic properties such as local photoluminescence (PL), charge carrier lifetimes, and mobilities. We observe a local enhancement and shift of the PL emission at different regions of the FIRA clusters, but we observe no effect of crystal orientation on the optoelectronic properties. Additionally, despite substantial differences in grain size between the two systems, we find similar optoelectronic properties. These findings show that optoelectronic quality is not necessarily related to the orientation and size of crystalline domains.

Crystal Orientation and Grain Size: Do They Determine Optoelectronic Properties of MAPbI3 Perovskite?

Environmental-Friendly Urea Additive Induced Large Perovskite Grains for High Performance Inverted Solar Cells

Mid-infrared single photon detector with superconductor Mo0.8Si0.2 nanowire

Niobium nitride (NbN) nanowires have a high repetition rate and efficiency, making them ideal for superconducting nanowire single photon detectors (SNSPDs). However, it is difficult to fabricate NbN arrays over large areas, which is critical for various applications. This paper describes a 4 × 4 NbN SNSPD array (16 pixels) and optical coupling with a 300-μm-diameter multimode fiber using beam compression technology. This is the first NbN SNSPD coupled with such large-diameter fibers. The designed pixels are positioned as closely as possible (pixel filling factor about 98.5%), almost without dead area between them. This results in a system efficiency of 46% and a quantum efficiency of 94.5% for photons (λ = 1064 nm) coupled from multimode fibers. An intrinsic time resolution of less than 69 ps can be obtained. The proposed high-performance single photon detector is suitable for satellite laser ranging. Furthermore, the proposed system is feasible for large SNSPD arrays with NbN, paving the way for the development of efficient photon cameras with NbN nanowires.

/pdf/sixteen-pixel-nbn-nanowire-single-photon-detector-coupled-zcwgkeoigb.pdf

Sixteen-Pixel NbN Nanowire Single Photon Detector Coupled With 300-μm Fiber

Laser communication using photons should consider not only the transmission environment’s effects, but also the performance of the single-photon detector used and the photon number distribution. Photon communication based on the superconducting nanowire single-photon detector (SNSPD) is a new technology that addresses the current sensitivity limitations at the level of single photons in deep space communication. The communication’s bit error rate (BER) is limited by dark noise in the space environment and the photon number distribution with a traditional single-pixel SNSPD, which is unable to resolve the photon number distribution. In this work, an enhanced photon communication method was proposed based on the photon number resolving function of four-pixel array SNSPDs. A simulated picture transmission was carried out, and the error rate in this counting mode can be reduced by 2 orders of magnitude when compared with classical optical communication. However, in the communication mode using photon-enhanced counting, the four-pixel response amplitude for counting was found to restrain the communication rate, and this counting mode is extremely dependent on the incident light intensity through experiments, which limits the sensitivity and speed of the SNSPD array’s performance advantage. Therefore, a BER theoretical calculation model for laser communication was presented using the Bayesian estimation algorithm in order to analyze the selection of counting methods for information acquisition under different light intensities and to make better use of the SNSPD array’s high sensitivity and speed and thus to obtain a lower BER. The counting method and theoretical model proposed in this work refer to array SNSPDs in the deep space field.

Enhanced photon communication through Bayesian estimation with an SNSPD array

Amorphous materials are attractive candidates for fabricating the superconducting nanowire single-photon detectors (SNSPDs) due to their superior tolerance and scalability over crystalline niobium nitride. However, the reduced superconducting transition temperature degenerates both operating temperature and saturation efficiency. Herein, the SNSPD (6.5 nm thickness and 50 nm width) based on the amorphous Mo0.8Si0.2 film with a high optical absorption coefficient demonstrates close-to-unity intrinsic detection efficiency for 1550 nm photons from 75 mK to 2.2 K. Further, a high-performance array SNSPD with optimized 90 nm-width wires is also demonstrated. As-fabricated uniform 4-pixel SNSPD exhibits a saturation plateau for the photon counts at 2.2 K, which overcomes the limitation of operation at low temperature (<1  K) for traditional amorphous SNSPDs. Coupled with superior intrinsic quantum efficiency, highly efficient photon counts, and low dark count ratio, this detector paves a way for achieving high efficiency and superior yield for large array systems.

Biao Zhang

Papers

Environmental-Friendly Urea Additive Induced Large Perovskite Grains for High Performance Inverted Solar Cells

Mid-infrared single photon detector with superconductor Mo0.8Si0.2 nanowire

Sixteen-Pixel NbN Nanowire Single Photon Detector Coupled With 300-μm Fiber

Enhanced photon communication through Bayesian estimation with an SNSPD array

Saturation efficiency for detecting 1550 nm photons with a 2 × 2 array of Mo 0.8 Si 0.2 nanowires at 2.2 K