Perovskite semiconductors for direct X-ray detection and imaging

Halide perovskites have emerged as the next generation of optoelectronic materials and their remarkable performances have been attractive in the fields of solar cells,light-emitting diodes,photodetectors,etc.In addition,halide perovskites have been reported as an attractive new class of X-ray direct detecting materials recently,owning to the strong X-ray stopping capacity,excellent carrier transport,high sensitivity,and cost-effective manufacturing.Meanwhile,perovskite based direct Xray imagers have been successfully demonstrated as well.In this review article,we firstly introduced some fundamental principles of direct X-ray detection and imaging,and summarized the advances of perovskite materials for these purposes and finally put forward some needful and feasible directions.

Solution-processed halide perovskite microcavity exciton-polariton light-emitting diodes working at room temperature

Exciton-polaritons offer the potential to achieve electrically pumped perovskite polariton lasers with much lower current thresholds than conventional photonic lasers. While optically pumped exciton-polaritons have been widely studied in halide perovskites, electrically-pumped polaritons remain limited. In this study, we demonstrate the use of a solution-processing strategy to develop halide perovskite polariton light-emitting diodes(LEDs) that operate at room temperature. The strong coupling of excitons and cavity photons is confirmed through the dispersion relation from angle-resolved reflectivity, with a Rabi splitting energy of 64 meV. Our devices exhibit angle-resolved electroluminescence following the low polariton branch and achieve external quantum efficiencies of 1.7%, 3.85%, and 3.7% for detunings of 1.1,-77, and-128 meV, respectively. We also explore devices with higher efficiency of 5.37% and a narrower spectral bandwidth of 6.5 nm through the optimization of a top emitting electrode. Our work demonstrates, to our knowledge, the first room-temperature perovskite polariton LED with a typical vertical geometry and represents a significant step towards realizing electrically pumped perovskite polariton lasers.

Low-dose real-time X-ray imaging with nontoxic double perovskite scintillators

X-rays are widely used in probing inside information nondestructively,enabling broad applications in the medical radiography and electronic industries.X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently.However,the strong self-absorption,relatively low light yield and lead toxicity of these perovskites restrict their practical applications.Here,we report a series of nontoxic double-perovskite scintillators of Cs_(2)Ag_(0.6)Na_(0.4)In_(1-y)Bi_(y)Cl_(6).By controlling the content of the heavy atom Bi^(3+),the X-ray absorption coefficient,radiative emission efficiency,light yield and light decay were manipulated to maximise the scintillator performance.A light yield of up to 39,000±7000 photons/MeV for Cs_(2)Ag_(0.6)Na_(0.4)In_(0.85)Bi_(0.15)Cl_(6) was obtained,which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr_(3)(21,000 photons/MeV).The large Stokes shift between the radioluminescence(RL)and absorption spectra benefiting from self-trapped excitons(STEs)led to a negligible selfabsorption effect.Given the high light output and fast light decay of this scintillator,static X-ray imaging was attained under an extremely low dose of ∼1μGy_(air),and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2μGy_(air) s^(−1).After thermal treatment at 85℃ for 50 h followed by X-ray irradiation for 50 h in ambient air,the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged.Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites,not only for avoiding toxicity but also for better performance.

Dopant-free hole transporting materials with supramolecular interactions and reverse diffusion for efficient and modular p-i-n perovskite solar cells

The rational design of dopant-free organic hole-transporting layer(HTL) materials is still a challenge for realizing high-efficient and stable p-i-n planar perovskite solar cells(pero-SCs). Here, we synthesized two π-conjugated small-molecule HTL materials through tailoring the backbone and conjugated side chain to carefully control molecular conformation. The resultant BDT-TPAs Th containing a planar fused benzo[1,2-b:4,5-b′]dithiophene(BDT) core and a conjugated thiophene side chain showed the planar conformation. X-ray crystallography showed a favorable stacking model in solid states under the parallel-displaced π-πand additional S-π weak-bond supramolecular interactions, thus achieving an obviously increased hole mobility without dopants.As an HTL material in p-i-n planar pero-SCs, the marginal solubility of BDT-TPA-s Th enabled inverse diffusion into the perovskite precursor solution for assisting the subsequent perovskite film growth and passivating the uncoordinated Pb2+ ion defects. As a result, the planar p-i-n pero-SCs exhibited a champion power conversion efficiency(PCE) of 20.5% and enhanced moisture stability. Importantly, the BDT-TPA-s Th HTL material also showed weak thickness-photovoltaic dependence, and the pero-SCs with blade-coated BDT-TPA-s Th as a HTL achieved a 15.30% PCE for the 1-cm2 modularized device. This HTL material design strategy is expected to pave the way toward high-performance, dopant-free and printing large-area planar p-i-n pero-SCs.

Efficiency breakthrough for all-perovskite tandem solar cells

The power conversion efficiency(PCE)of single-junction perovskite solar cells(PSCs)has rapidly boosted to 25.2%[1],approaching the Shockley-Queisser limit.A potential strategy to further elevate the PCE of single-junction PSCs is to fabricate all-perovskite tandem solar cells[2,3],which is composed of a wide-bandgap(1.7–1.9 eV)top sub-cell and a low-bandgap(0.9–1.2 eV)bottom sub-cell.

19.34 cm2 large-area quaternary organic photovoltaic module with 12.36% certified efficiency

In this study, a quaternary blending strategy was applied in the fabrication of organic photovoltaic devices and large-area modules. As a result, the ultimate quaternary organic solar cells(OSCs) deliver 16.71% efficiency for small-area devices and 13.25% for large-area(19.34 cm2) modules(certified as 12.36%), which is one of the highest efficiencies for organic solar modules to date. Our results have proved the synergistic effects of multiple components in OSCs, providing an effective strategy for achieving high-performance organic photovoltaic devices and modules.

Large-area perovskite solar cells

Perovskite solar cells(PSCs)have been attracting much attention during the past years due to the advantages of perovskite materials such as high light absorption coefficient,excellent charge mobility,long charge diffusion length,tunable direct band gap,low cost,etc.,exhibiting great potential as the next-generation photovoltaic technology[1–3].

Advances in halide perovskite semiconductors for energy-integrated and energy-resolved X-ray detection

X-ray andγ-ray detectors are widely used in medical,military,security,material analysis,and industrial inspection.In recent years,perovskite materials have become promising materials for radiation detection owing to their strong stopping power,considerable carrier transportation ability,and simple synthesis process.Previous studies have demonstrated both direct and indirect radiation detectors using perovskite materials.In this review,we aim to elucidate the mechanism by which X-rays andγ-rays interact with matter,explain the principles of the energy integrating mode and photon counting mode for direct detection,and discuss the key factors determining device performance.Furthermore,we summarize recent advances in perovskite-based radiation detectors for both modes.Additionally,we identify challenges that need to be overcome to enable perovskite materials to be successfully commercialized.