low-carbon and renewable clean energy due to its high carrier mobility, wide absorbance, low exciton energy, long carrier lifetime and diffusion length, high defect tolerance and low-cost preparation. [9,10] Researchers have made considerable effort to improve the power conversion efficiency (PCE) and longterm stability of PSCs. In 2009, MAPbBr 3 (MA = methylamine, CH 3 NH 2 ) was used as a new dye in a dye-sensitized solar cell. [3] Later, all-solid-state perovskite solar cells were prepared in 2012. [11,12] During the first stage, researchers attempted to improve the preparation technology for the solid perovskite absorber. The anti-solvent method, gas pumping, blade coating, vacuum deposition, magnetron sputtering, and other methods have been developed to eliminate macro defects such as pin holes and prepare dense thin films of perovskites. [13] Micro-defects, such as point defects in the bulk, grain boundaries, dangling bonds on the film surface and interfacial stress from thermal mismatch, have also been reduced by additive engineering, solvent engineering, composite engineering and strain engineering. [14] After great effort, the efficiency and long-term stability of PSCs have been improved considerably. However, the mechanisms of how efficiency and stability are affected by bandgap, trap density, grain boundaries, carrier lifetime and film roughness remain unknown due to too many involved parameters.Understanding the key factor driving the efficiency and stability of semiconductor devices is vital. To date, the key factor influencing the long-term stability of perovskite solar cells (PSCs) remains unknown because of the many influencing factors. In this work, through machine learning, the influences of five factors, including grain size, defect density, bandgap, fluorescence lifetime, and surface roughness, on the efficiency and stability of PSCs have been revealed. It is found that the bandgap has the greatest influence on the efficiency, and the surface roughness and grain size are most influential to the long-term stability. A mathematical model is given to predict efficiency based on fluorescence lifetime and bandgap. Guided by the model, four groups of experiments are conducted to confirm the machine-learning predictions and a PSC with 23.4% efficiency and excellent long-term stability is obtained, as manifested by retention of 97.6% of the initial efficiency after 3288 h aging in the ambient environment, the best stability under these conditions. This work shows that machine learning is an effective means to enrich semiconductor physical models.
Lead‐free A3Bi2I9‐type perovskites are demonstrated as a class of promising semiconductors for high‐performance X‐ray detection due to their high bulk resistivity and strong X‐ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c‐axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A‐site cation of aminoguanidinium (AG) with all‐NH2 terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG3Bi2I9 single crystals (SCs) render shorter interlamellar distance for a larger mobility‐lifetime product of 7.94 × 10−3 cm2 V−1, which is three times higher than the value measured on the best MA3Bi2I9 SC (2.87 × 10−3 cm2 V−1). Therefore, the X‐ray detectors fabricated on the AG3Bi2I9 SC exhibit high sensitivity of 5791 uC Gy−1 cm−2, a low detection limit of 2.6 nGy s−1, and a short response time of 690 µs, all of which are far better than those of the state‐of‐the‐art MA3Bi2I9 SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lp mm−1) X‐ray imaging. This work will facilitate the development of low‐cost and high‐performance lead‐free X‐ray detectors.
Theoretical analyses indicate that a two-dimensional (2D) layered metal halide perovskite, with its unique quantum-well structure and large exciton binding energy, should render both fast and strong fluorescence, making it ideal for fast X-ray imaging. Herein, an airflow-controlled solvent evaporation system is designed to grow an inch-sized 2D (PEA) 2 PbBr 4 single crystal (SC) at low temperature (30 °C). Under X-rays, the (PEA) 2 PbBr 4 SC exhibits a high light yield of 73226 photons/MeV and a fast response time of 14 ns, which is approximately 1.4 times higher and 75 times faster than those of the commercial CsI:Tl scintillator (54000 photons/MeV and 1049 ns), respectively. With such significant merits, an X-ray imager is assembled by integrating a (PEA) 2 PbBr 4 SC with dimensions of 57 × 41 mm 2 for X-ray imaging, and a high spatial resolution of 11.1 lp/mm is achieved, which demonstrates the application prospect of the large-size (PEA) 2 PbBr 4 SC in high-speed nondestructive medical diagnosis.
The perovskite layer contains a large number of charged defects that seriously impair the efficiency and stability of perovskite solar cells (PSCs), thus it is essential to develop an effective passivation strategy to heal them. Based on theoretical calculations, it is found that enhancing the electrostatic potential of passivators can improve passivation effect and adsorption energy between charged defects and passivators. Herein, an electrostatic potential modulation (EPM) strategy is developed to design passivators for highly efficient and stable PSCs. With the EPM strategy, 1‐phenylethylbiguanide (PEBG) and 1‐phenylbiguanide (PBG) are designed. It is found that the charge distribution and electrostatic potential of phenyl‐ and phenylethyl‐ substituent on the biguanide are significantly enhanced. The N atom directly bonding to the phenyl group shows larger positive charge than that bonding to the phenylethyl group. The modulated electrostatic potential makes PBG bind stronger with the defects on perovskite surface. Based on the effective passivation of EPM, a champion efficiency of 24.67% is realized and the device retain 91.5% of its initial PCE after ≈1300 h. The promising EPM strategy, which provides a principle of passivator design and allows passivation to be controllable, may advance further optimization and application of perovskite solar cells toward commercialization.
Effective modification of the structure and properties of halide perovskites via the pressure engineering strategy has attracted enormous interest in the past decade. However, sufficient effort and insights regarding the potential properties and applications of the high-pressure amorphous phase are still lacking. Here, the superior and tunable photoelectric properties that occur in the pressure-induced amorphization process of the halide perovskite Cs 3 Bi 2 I 9 are demonstrated. With increasing pressure, the photocurrent with xenon lamp illumination exhibits a rapid increase and achieves an almost five orders of magnitude increment compared to its initial value. Impressively, a broadband photoresponse from 520 to 1650 nm with an optimal responsivity of 6.81 mA W −1 and fast response times of 95/96 ms at 1650 nm is achieved upon successive compression. The high-gain, fast, broadband, and dramatically enhanced photoresponse properties of Cs 3 Bi 2 I 9 are the result of comprehensive photoconductive and photothermoelectric mechanisms, which are associated with enhanced orbital coupling caused by an increase in Bi-I interactions in the [BiI 6 ] 3− cluster, even in the amorphous state. These findings provide new insights for further exploring the potential properties and applications of amorphous perovskites.
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