All-vacuum deposited and thermally stable perovskite solar cells with F4-TCNQ/CuPc hole transport layer.

Hole transporting layers (HTLs) play a crucial role in the realization of efficient and stable perovskite solar cells (PSCs). Copper phthalocyanine (CuPc) is a promising HTL owing to its thermal stability and favorable band alignment with the perovskite absorber. However, the power conversion efficiency (PCE) of PSCs with a CuPc HTL is still lagging behind highly efficient solar cells. Herein, a p-type tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) is employed as an interlayer between the perovskite and CuPc HTL in all-vacuum deposited PSCs. The F4-TCNQ interlayer improves the conductivity of both MAPbI3 and CuPc, reduces the shunt pathway and facilitates an efficient photoexcited holes transfer from the valance band of the MAPbI3 to the LUMO of the F4-TCNQ. Consequently, the best solar cell device with an F4-TCNQ interlayer achieved a PCE of 13.03% with a remarkable improvement in fill factor. Moreover, the device showed superior stability against thermal stress at 85 °C over 250 h and retained ∼95% of its initial efficiency. This work demonstrates a significant step towards all-vacuum deposited perovskite solar cells with high thermal stability.

CH3NH3PbBr3 Quantum Dot-Induced Nucleation for High Performance Perovskite Light-Emitting Solar Cells.

Solution-processed organometallic halide perovskites have obtained rapid development for light-emitting diodes (LEDs) and solar cells (SCs). These devices are fabricated with similar materials and architectures, leading to the emergence of perovskite-based light-emitting solar cells (LESCs). The high quality perovskite layer with reduced nonradiative recombination is crucial for achieving a high performance device, even though the carrier behaviors are fundamentally different in both functions. Here CH3NH3PbBr3 quantum dots (QDs) are first introduced into the antisolvent in solution phase, serving as nucleation centers and inducing the growth of CH3NH3PbI3 films. The heterogeneous nucleation based on high lattice matching and a low free-energy barrier significantly improves the crystallinity of CH3NH3PbI3 films with decreased grain sizes, resulting in longer carrier lifetime and lower trap-state density in the films. Therefore, the LESCs based on the CH3NH3PbI3 films with reduced recombination exhibit improved electroluminescence and external quantum efficiency. The current efficiency is enhanced by 1 order of magnitude as LEDs, and meanwhile the power conversion efficiency increases from 14.49% to 17.10% as SCs, compared to the reference device without QDs. Our study provides a feasible method to grow high quality perovskite films for high performance optoelectronic devices.

Atomic resolution imaging of beryl: an investigation of the nano-channel occupation.

Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ring-silicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be3 Al2 Si6 O18 ) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions.

Compensator-based intensity-modulated radiotherapy in head and neck cancer: our experience in achieving dosimetric parameters and their clinical correlation.

AIMS: To review the Batra Hospital and Medical Research Centre experience of using compensator-based intensity-modulated radiotherapy (IMRT) to treat head and neck cancer. MATERIALS AND METHODS: Between October 2003 and August 2004, 18 patients underwent IMRT for head and neck cancer at our institution. IMRT was delivered using partial transmission high-resolution compensator blocks. RESULTS: With a median follow-up of 13.3 months, two patients had residual disease and two failed in the gross tumour volume (GTV). The complete response rate after surgical salvage was 94.5%. Both the locoregional relapse-free and disease-free survival rates were 81.8%. The target coverage in terms of average maximum, mean and minimum dose (in Gy) delivered was 78.6, 73.5 and 58.4 to the GTV-planning target volume, 82.3, 70.9 and 47.3 to clinical target volume 1 (CTV1) and 82.9, 66.2 and 29.6 to CTV2. The dose constraint of 30 Gy to less than 50% of the contralateral parotid volume was achieved in 12 (66.7%) patients. If the dose constraint was revised to 35 Gy, at least 50% of the parotid volume was spared in 17 (94.5%) patients. On average, 75% of the contralateral parotid volume received a dose less than 35 Gy in 13 (72.3%) patients with grade I xerostomia, whereas this was 49.3% in five (27.7%) patients with grade II xerostomia, and the difference was statistically significant (P = 0.001). CONCLUSIONS: In our initial experience, compensator-based IMRT is feasible with regard to target coverage and parotid volume sparing. The parotid volume dose has significant clinical implications on the grade of xerostomia. Our results invoke rethinking into the issues of the parotid volume dose constraint in our subpopulation.