D-π-D molecular layer electronically bridges the NiO_(x) hole transport layer and the perovskite layer towards high performance photovoltaics

Nickel oxide (NiO_(x)) has significant cost and stability advantages over poly[bis (4-phenyl)(2,4,6-trimethyl phenyl)amine](PTAA) for inverted p-i-n perovskite solar cells (PSCs),but the poor NiO_(x)/perovskite contact stemming from some reactive species at the interface led to suboptimal device performance.To solve this problem,we take a multiple donor molecule approach,using 3,3’-(4,8-bis(hexylthio)benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl)bis(10-(6-bromohexyl)-10H-phenoxazine)(BDT-POZ) as an example,to modify the NiO_(x)/perovskite interface.The primary goal was to reduce the under-coordinated Ni^(≥3+) cations via electron transfer from the donor molecules to NiO_(x),thus mitigating the detrimental reactions between perovskite and NiO_(x).Equally importantly,the hole extraction at the interface was greatly enhanced after the organic donor modification,since the hydrophobic species atop NiO_(x) not only enabled pinhole-free crystallization of the perovskite but also properly tuned the interfacial energy level alignment.Consequently,the PSCs with NiO_(x)/BDT-POZ HTL achieved a high power conversion efficiency (PCE) up to 20.16%,which compared excellently with that of the non-modified devices (17.83%).This work provides a new strategy to tackle the exacting issues that have so far impeded the development of NiO_(x) based PSCs.

一种量身定制的双锥形光纤阵列使最先进的闪烁体成为可能

Scintillators, capable of converting X-/γ-ray to light, find widespread applications in medical diagnostics, industrial product inspection, security screening, and high-energy physics [1], [2]. Despite the significant success, the growing need of peeking deep into matters in different modalities calls for the revolution of current scintillators. Apart from the ongoing goal of reducing radiation dosage, entailing scintillators with mechanical flexibility and ultrahigh spatiotemporal resolution is now at the forefront [3], [4]. For example, if the scintillator is made flexible, three-dimensional (3D) imaging of curved objects can be enabled without the use of multi-angle scanning and algorithmic image reconstruction [5].

Revealing the crystallization process and realizing uniform 1.8 eV MA-based wide-bandgap mixed-halide perovskites via solution engineering

Wide-bandgap perovskites are recently drawing tremendous attention in the community for high-efficiency all-perovskite tandem solar cells.However,the formamidinium (FA^+) and methylammonium (MA^+) based wide-bandgap mixed halide perovskites suffered from high density of traps and pin-holes,respectively.Fundamental understanding on the crystallization and film formation processes are keys to overcome those challenges but not yet clearly understood.In this study,an in-situ photoluminescence technique was used to investigate the perovskite crystallization during the thermal annealing process.It is found that the crystallization of a mixed halide perovskite with bromide (Br^-) and iodine (I^-) ions following the Ostward ripening crystal growth.Interestingly,it is found that the initial nucleation reaction is quickly completed in the first few seconds,however,leaving the small crystals with inhomogeneous composition.The different aggregation affinities of such inhomogeneous small crystals provoke the formation of pin-holes during the thermal annealing process.By engineering the precursor solution to control the nucleation rate,the chemical composition of the small crystals has become homogenous.Uniform pin-hole free high Br-composited wide-bandgap MA0.9Cs0.1Pb(I0.6Br0.4)3 perovskite films with bandgap energy of 1.8 eV have been realized.The corresponding photovoltaic devices have achieved an encouraging device efficiency of 15.1% with superb photostability.