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Near-infrared (NIR) II detection at weak flux intensity is required in medical imaging and is especially urgent in light of the low quantum efficiency of NIR-II dyes. The low responsivity of traditional photodetectors in this region limits image quality. Here, we report a NIR-II photodetector with high gain based on perovskite coupled PbS colloidal quantum dots (CQDs). Tailoring the trap density of CQDs by designing surface ligands with dual functionality contributed to control over trap-induced charge-injection upon light illumination. As a result, a detector with high gain is realized, showing external quantum efficiency of 1260% at 1200 nm and achieving the lowest detectable light intensity, that is, as low as 0.67 pW cm

Solution-processed perovskites as emerging semiconductors have achieved unprecedented milestones in sensor optoelectric devices. Stability along with the device noise issues are the major obstacle for photodetectors to compete with the traditional devices. Here, we demonstrated that l-ascorbic acid (l-AA) as a polyhydroxy ester can coordinate with the amino group of formamidine cations (FA+) through multiple hydrogen bond interactions to stabilize the perovskite, which protect the FA+ ions from nucleophile attack and effectively suppress the degradation of FA+ ions, improving the perovskite stability and suppressing the device noise to below 0.3 pA Hz-1/2 with a large linear dynamic range of 239 dB. The dual functions of l-AA enable the perovskite photodetector to have a high detectivity of 1012 Jones. The self-powered device works with no energy consumption and maintains an undegraded performance over 1200 h of inspection at ambient conditions, which is promising for infrastructure construction, signal sensing, and real-time information delivery.

Halide perovskite solar cells have achieved unprecedented progress in efficiency and high-throughput module manufacturing; however, the stability of perovskite devices remains to be a major obstacl...

Organic–inorganic halide perovskites have emerged as a promising semiconductor family because of their remarkable performance in optoelectronic devices. On the other hand, the stability of perovskites remains a critical issue. In this work, we report a quantitative and systematic investigation of in situ cleaved MAPbBr3 single-crystal degradation processes in X-ray, N2, O2, and H2O environments. The high-quality crystals were monitored by high-resolution X-ray photoelectron spectroscopy with careful control of the exposure time and pressure. The detailed electronic structure and compositional changes of the crystal were tracked throughout the different exposures, and these studies provided insights into the various degradation mechanisms. We identified that ∼10% of the surface MAPbBr3 degraded to metallic lead under X-rays in vacuum, while N2 could protect the sample from the degradation for 9 h under the same condition. Other measurements showed that while the surface was not sensitive to pure O2, it was...

The efficiency of a solar cell generally decreases over time due to degradation of the devices. Here we report a spontaneous increase of device efficiency for organic–inorganic hybrid perovskite (OIHP) solar cells after a period of storage that is speculated to be related to the sodium ions (Na+) diffused from the substrate. The efficiency of a p–i–n planar heterojunction structure device rises from 18.8 to 20.2% after 24 h of storage in nitrogen. The increased efficiency can be explained by the prolonged carrier lifetime and reduced trap density in the OIHP films. The expected contribution by Na+ in defect passivation has been evidenced by studying the evolution of the film’s photoluminescence (PL) lifetime, trap density, and device efficiency over storage duration on varied substrates that either contain Na+ or do not. The passivation effect of Na+ is further identified by the improved PL lifetime observed in the OIHP film made on a silicon substrate with intentionally added Na+.

Due to their environmentally friendly ideology, aqueous-processed hybrid solar cells (HSCs) are favored for industrial production. However, relatively low device performance urges the progress in power conversion efficiency (PCE) for their further applications. In this work, the function of polymer and nanocrystal (NC) is studied by investigating three different device structures. The polymer (low hole mobility), which plays an important role even if the content is extremely low, is mainly responsible for enhancing the Voc and FF, while the NC (high hole mobility) is the principle part in light absorbing, carrier generating, and transporting. The intensive study of polymer and NC makes it possible to achieve high performance through adjusting the thickness of different active layers by using device structures of the cathode/electron transport layer (ETL)/NC/polymer:NC/hole transport layer (HTL)/anode. An efficient aqueous-processed HSC with PCE of 5.64% is obtained which presents the highest performance a...

Aqueous-processed solar cells have evolved into a new generation of promising and renewable energy materials due to their excellent optical, electrical, and low-cost properties. In this work, Cd0.75Hg0.25Te colloid quantum dots (CQDs) were incorporated into a water-soluble conjugated polymer with broad absorption and high charge-carrier-mobility (5 × 10(-4) cm(2) V(-1) s(-1)) to obtain a composite with an absorption spectrum ranging from 300 to 1200 nm. The matched energy level between polymer and CQDs ensured the effective electron transfer, while the interpenetrating network structure formed via heat treatment guaranteed the quick electron transport. Moreover, the formation process of the interpenetrating network was systematically monitored by using AFM and TEM instruments and further confirmed through the measurement of charge-carrier-mobility of the active layers. In combination with the surface modification of a single Cd0.75Hg0.25Te layer, this aqueous-processed solar cell showed excellent photovoltaic response and the power conversion efficiency (PCE) reached 2.7% under AM 1.5 G illumination (100 mW cm(-2)). Especially, the contribution of the Herschel infrared region (780-1100 nm) to the photocurrent was as high as 15.04%. This device showed the highest PCE among organic-inorganic hybrid solar cells (HSCs) based on CdxHg1-xTe CQDs and the highest near infrared (NIR) contribution among aqueous-processed HSCs, indicating the enormous potential of taking advantage of NIR energy in a solar spectrum and a promising application in solar cells especially used in cloudy weather.

In this work, we investigated the correlation between the inner structure of aqueous solution processed polymer:nanocrystals (NCs) hybrid solar cells and its performance. By altering the compositional concentration, annealing temperature, annealing time, and the thickness of the active layer, the diameter of CdTe NCs increased from 2.8 nm to tens of nanometers. Also, the performance of poly (1,4-phenylene vinylene) (PPV):CdTe hybrid solar cells changed accordingly. Systematical analysis revealed that the best performance of hybrid solar cells was achieved when CdTe was 30 mg/mL and the annealing temperature was above 250 °C with the active layer thickness of about 100 nm. The inner structure showed the size of CdTe NCs was around 26 nm, with the spacing of 6–12 nm. The data of transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that the CdTe NCs grew mainly via dynamic coalescence.

Poly(1,4-naphthalenevinylene), prepared from a water-soluble precursor, was used to fabricate hybrid solar cells by blending with water-soluble CdTe nanocrystals (NCs) to act as the photoactive layer. In composites with CdTe NCs as the electron acceptors in a bulk heterojunction configuration, the devices exhibited a short-circuit current density of -6.14 mA/cm(2), an open-circuit voltage of 0.44 V, a fill factor of 0.32, and a power conversion efficiency of 0.86% under AM1.5G conditions. Because the devices were fabricated from water-soluble materials, the procedure was generally simple and environmentally friendly in comparison to the conventional devices fabricated from oil-soluble materials.

In this paper, we demonstrated a modified hot-injection method to synthesize high-quality Cu2–xSe nanocrystals (NCs) in liquid paraffin without using the hazardous and unstable alkylphosphines as the ligand of Se. The key of this method is the capability for tuning the reactivity of Se at the stage of formation of Cu2–xSe nuclei. The low reactivity of Se facilitated the decomposition of copper(II) acetylacetonate into Cu2O, whereas the increase of Se reactivity promoted the reaction between Cu and Se. By control of the experimental variables, such as reaction time, Se concentration, reaction temperature, and, particularly, the addition of the noncoordinating solvent of Se, high-quality Cu2–xSe NCs were prepared. The resultant Cu2–xSe NCs possessed an indirect band-gap absorption around 1050 nm, potentially applicable in photovoltaic investigations. As an example, the optoelectronic properties of Cu2–xSe NCs were investigated, which showed a promising increase in photocurrent under AM 1.5 illumination. Bec...