There is little question that the 'electronic revolution' of the 20 th century has impacted every aspect of humanity. However, the emergence of solid-state electronics as a ubiquitous feature of an advanced modern society is posing new challenges that the management of electronic waste (e-waste) will remain through the 21 st century. In addition to developing strategies to manage such e-waste, further challenges can be identified concerning the conservation and recycling of scarce elements, reducing the W. Li and Q. Liu contributed equally to this work. A. K. K. Kyaw is grateful to Guangdong University Key Laboratory for Advanced Quantum Dot Displays and Lighting (No. 2017KSYS007); Shenzhen Science, Technology and Innovation Commission (No. JCYJ20180305180645221); Guangdong Basic and Applied Basic Research Foundation (No. 2020A1515010916); and High-level University Fund (G02236004). Q. Liu wishes to thank Queensland University of Technology (QUT) for offering a scholarship through the QUT Postgraduate Research Award (QUTPRA) to conduct his research. P. S.wishes to thank QUT for the financial support from the Australian Research Council (ARC) for the Future Fellowship (FT130101337) and QUT core funding (QUT/322150-0301/07).

Recently, lead sulfide (PbS) quantum dots (QDs) have demonstrated great potential in becoming one of the most promising next-generation photoelectrical materials for photodetectors. PbS QDs provide fascinating properties including size-controllable spectral sensitivity, a wide and tunable absorption range, cost-efficient solution processability, and flexible substrate compatibility. One of the key problems that limit the performance of PbS QDs-based photodetectors is inefficient carrier transfer. Long ligands decorating the outside surface of PbS QDs to protect them against degeneration inhibit the transfer of electrical charge carriers and thereby limit the device performance. To overcome this problem, the long ligands need to be effectively exchanged. Here, a two-step ligand-exchange method is demonstrated. The QDs are pretreated using methylammonium iodide in solution as the first step ligand exchange before the layer-by-layer deposition process and solid-state ligand exchange. The grazing-incidence small-angle X-ray scattering and X-ray photoelectron spectroscopy analyses prove a smaller spacing among the QDs and an increased ligand-exchange ratio by adopting the two-step method. This strongly indicates a better capability of charge transfer than the traditional one-step solid-state ligand-exchange technology. Devices fabricated using the two-step method present an enhancement of the charge-transfer capability with a larger current. The efficient charge transfer is further demonstrated by a significant 94% increase of the responsivity and a 57% enhancement of the detectivity of the PbS QDs-based photodetector, reaching 3302 mA/W and 5.06 × 1012 J, respectively.

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Organic solar cells (OSCs) based on polymer donor and non-fullerene acceptor achieve power conversion efficiency (PCE) more than 19% but their poor absorption below 550 nm restricts the harvesting of high-energy photons. In contrast, wide bandgap all-inorganic perovskites limit the absorption of low-energy photons and cause serious below bandgap loss. Therefore, a 2-terminal (2T) monolithic perovskite/organic tandem solar cell (TSC) incorporating wide bandgap CsPbI 2 Br is demonstrated as front cell absorber and organic PM6:Y6 blend as rear cell absorber, to extend the absorption of OSCs into high-energy photon region. The perovskite sub-cell, featuring a sol-gel prepared ZnO/SnO 2 bilayer electron transporting layer, renders a high open-circuit voltage (V OC ). The V OC is further enhanced by employing thermal annealing (TA)-free process in the fabrication of rear sub-cell, demonstrating a record high V OC of 2.116 V. The TA-free Ag/PFN-Br interface in organic sub-cell facilitates charge transport and restrains nonradiative recombination. Consequently, a remarkable PCE of 20.6% is achieved in monolithic 2T-TSCs configuration, which is higher than that of both reported single junction and tandem OSCs, demonstrating that tandem with wide bandgap all-inorganic perovskite is a promising strategy to improve the efficiency of OSCs.

For organic-inorganic perovskite to be considered as the most promising materials for light emitting diodes and solar cell applications, the active materials must be proven to be stable under various conditions, such as ambient environment, heat and electrical bias. Understanding the degradation process in organic-inorganic perovskite light emitting diodes (PeLEDs) is important to improve the stability and the performance of the device. We revealed that electrical bias can greatly influence the luminance and external quantum efficiency of PeLEDs. It was found that device performance could be improved under low voltage bias with short operation time, and decreased with continuous operation. The degradation of perovskite film under high electrical bias leads to the decrease of device performance. Variations in the absorption, morphology and element distribution of perovskite films under different electrical bias revealed that organic-inorganic perovskites are unstable at high electrical bias. We bring new insights in the PeLEDs which are crucial for improving the stability.