ABSTRACT
In this paper, we reported the in situ fabrication of highly luminescent formamidinium lead bromide (FAPbBr3) nanocrystal thin films by dropping toluene as an anti-solvent during the spin-coating with a perovskite precursor solution using 3,3-diphenylpropylamine bromide (DPPA-Br) as a ligand. The resulting films are uniform and composed of 5-20 nm FAPbBr3 perovskite nanocrystals. By monitoring the solvent mixing of anti-solvent and precursor solution on the substrates, we illustrated the difference between the ligand-assisted reprecipitation (LARP) process and the nanocrystal-pinning (NCP) process. This understanding provides a guideline for film optimization, and the optimized films obtained through the in situ LARP process exhibit strong photoluminescence emission at 528 nm, with quantum yields up to 78% and an average photoluminescence lifetime of 12.7 ns. In addition, an exciton binding energy of 57.5 meV was derived from the temperature-dependent photoluminescence measurement. More importantly, we achieved highly efficient pure green perovskite based light-emitting diode (PeLEDs) devices with an average external quantum efficiency (EQE) of 7.3% (maximum EQE is 16.3%) and an average current efficiency (CE) of 29.5 cd A-1 (maximum CE is 66.3 cd A-1) by adapting a conventional device structure of ITO/PEDOT:PSS/TFB/perovskite film/TPBi/LiF/Al. It is expected that the in situ LARP process provides an effective methodology for the improvement of the performance of PeLEDs.
ABSTRACT
The high energy radiotherapy linear accelerators (LINAC) offer considerable risk of radiation hazards to patient, worker and public if adequate safety measures are not taken into the account. Proper bunker designing with appropriate shielding is an important safety measure, which protects workers and member of general public. The present study describes the details of shielding of LINAC bunker in four radiotherapy centers of Karachi city. In order to conduct the study, shielding of five LINAC installed in four radiotherapy centers was assessed by considering real occupancy factor, dose limits for worker and public, etc. to verify that shielding of the bunkers conforms to the national and international standards like International Atomic Energy Agency and National Council on Radiation Protection and Measurement. After the assessment, it was concluded that all bunkers conform to the radiation protection requirements and present adequate shielded. This is an important step to achieve as low as reasonably achievable principle and protect workers and member of general public.
