Arafat Mahmud

Simultaneous enhancement in stability and efficiency of low-temperature processed perovskite solar cells

Mixed ion based perovskite solar cells (PSCs) have recently emerged as a promising photoactive material owing to their augmented electronic and light harvesting properties combined with stability enhancing characteristics. However, to date most of the high performing perovskite devices employ a high temperature (∼500° C) sintering process for depositing a conventional titanium oxide (TiO2) based electron transport layer (ETL), which is a serious bottleneck towards roll-to-roll processing with flexible substrates, large scale manufacturability and also results in high energy consumption. The present work demonstrates simultaneous enhancement in efficiency and stability in the perovskite solar cell that is totally fabricated using low temperature methods with the synthesis process temperature not exceeding 150 °C at any stage. The perovskite devices, thus fabricated, exhibited high power conversion efficiency of ∼14.5% and device stability > 570 hours (normalized PCE to reach 80% of its original value), which is the first of this kind of accomplishment ever reported in entirely low temperature processed PSCs. It is noteworthy to mention that the presented devices utilize a ∼360 °C lower temperature than required for the conventional TiO2 based PSCs to achieve similar enhancements in terms of stability and efficiency simultaneously. The high performing PSCs reported in this work incorporate mixed organic perovskite (MA0.6FA0.4PbI3) as the light absorber and aluminium-doped zinc oxide (AZO) as the electron transport layer. Adding to the merits, the MA0.6FA0.4PbI3/AZO devices exhibited a substantially low photocurrent hysteresis phenomenon. In order to examine the underlying causes of the efficiency and stability enhancements in AZO based devices, a low temperature processed MA0.6FA0.4PbI3/ZnO device was also fabricated and comparatively studied. Investigations reveal that the improved dark carrier mobility and superior interfacial electronic properties at the perovskite/AZO interface are attributed to their enriched device performance. Slow perovskite decomposition rate/high device stability with AZO based perovskite devices was found to be associated with the more hydrophobic and acidic nature of the AZO surface and the related interfacial interactions with the adjacent perovskite layer.

Analysis of burn-in photo degradation in low bandgap polymer PTB7 using photothermal deflection spectroscopy

The efficiency of organic photovoltaic devices continues to increase; however, their limited stability is currently a barrier to the commercial prospects of the technology. Burn-in photo degradation, caused by continuous illumination under a light source, can cause a significant reduction in device performance. Our aim was to investigate this degradation pathway for the high-efficiency polymer PTB7, which was compared to the well-studied P3HT:PC71BM material system. In this study, we compared the burn-in aging profile for organic solar cells containing either P3HT or PTB7 as the donor polymer. This showed that PTB7:PC71BM solar cells exhibit a severe initial reduction in performance, due mainly to reduced short circuit current density (Jsc), during the 5 hour test period. P3HT:PC71BM cells were relatively stable during this test. Photothermal deflection spectroscopy (PDS), which provides sensitive measurement of sub bandgap absorption, was employed to discover the underlying mechanism causing this discrepancy. In PTB7-based devices, a significant increase in sub bandgap absorption was observed after illumination, which was attributed to the formation of sub bandgap trap states. This mechanism was identified as a contributing factor to the severe burn-in for PTB7-based organic solar cells. No such increase was observed for P3HT:PC71BM films.

Solution-Processed Lithium-Doped ZnO Electron Transport Layer for Efficient Triple Cation (Rb, MA, FA) Perovskite Solar Cells

The current work reports the lithium (Li) doping of a low-temperature processed zinc oxide (ZnO) electron transport layer (ETL) for highly efficient, triple-cation-based MA0.57FA0.38Rb0.05PbI3 (MA: methylammonium, FA: formamidinium, Rb: rubidium) perovskite solar cells (PSCs). Lithium intercalation in the host ZnO lattice structure is dominated by interstitial doping phenomena, which passivates the intrinsic defects in ZnO film. In addition, interstitial Li doping also downshifts the Fermi energy position of Li-doped ETL by 30 meV, which contributes to the reduction of the electron injection barrier from the photoactive perovskite layer. Compared to the pristine ZnO, the power conversion efficiency (PCE) of the PSCs incorporating lithium-doped ZnO (Li-doped) is raised from 14.07 to 16.14%. The superior performance is attributed to the reduced current leakage, enhanced charge extraction characteristics, and mitigated trap-assisted recombination phenomena in Li-doped devices, thoroughly investigated by means of electrochemical impedance spectroscopy (EIS) analysis. Li-doped PSCs also exhibit lower photocurrent hysteresis than ZnO devices, which is investigated with regard to the electrode polarization phenomena of the fabricated devices.

Cancer care scenario in Bangladesh

Bangladesh is a developing country that is facing many challenges, especially in the health sector. Cancer management is a priority due to the current trend of increased incidence in this region. In this article, the current scenario of cancer in Bangladesh and its management with brief history is outlined. The combined effort of government and private sector is highlighted with the gradual progress in cancer management. Recent introduction of the state-of-the-art facilities and the training facilities for human resource development are also outlined. The existing challenges and cooperation from local NGOs and other overseas sources are also highlighted to provide an insight regarding possible ways to tackle these challenges to ensure a better future.

Effect of PCBM film thickness on the performance of inverted perovskite solar cells

The effect of electron transportation layer (ETL) PCBM film thickness was investigated for the performance of inverted structure perovskite solar cells. The charge transportation study was carried by Mott-Schottky analysis. The result shows the charge transportation status of different electron thickness. A thicker PCBM layer could provide better diode property, while the thinner layer would lead to higher short circuit current. For this perovskite fabrication method, the thicker film worked better. This study reveals the optimization of PCBM depends on various factors, like cathode, and perovskite films. To further improve the efficiency of devices, the perovskite film and the design of device structure are needed to be optimized.

Hysteresis and electrode polarization in normal and inverted hybrid perovskite solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have demonstrated enormous potential to replace the traditional silicon photovoltaics. In spite of impressive progress, an in-depth understanding of various physiochemical and electronic properties of PSCs are yet to be unravelled. Anomalous hysteresis is one among them and its origin is a highly debated issue till date. In this work, the role of device structure and interfacial charge selective layer on the origin of hysteresis phenomenon was investigated. Normal devices with ZnO as electron transport layer exhibited excess interfacial capacitance in an order of magnitude higher than inverted devices with PCBM. Current-voltage characteristics correlated with capacitance measurements revealed that the electrode polarization as a consequence of ion migration and interfacial defect states might be a possible origin for hysteresis in PSCs.

Augmentation of optoelectronic properties via P3HT doping for low temperature processed perovskite solar cell

Methyl Ammonium Lead Halide Perovskite solar have shown immense potential to be a “Game Changer” in the photovoltaic industry. Major barriers to commercialization of Perovskite solar cells are poor device stability and high temperature requirement with TiO2 electron transport layer, widely used in efficient Perovskite devices. Apart from severe moisture sensitivity and thermal degradation, Perovskite layer can be decomposed due to the TBP additive incorporation with Li-TFSI dopant in most commonly used hole transport layers like Spiro OMeTAD and P3HT. Nearly 5000 C sintering temperature requirement for Titania electron transport layer also impedes the Perovskite manufacturing in roll-to-roll process on flexible substrate which has a stringent processing condition of sub 1500 C temperature. In this work, we have introduced F4TCNQ dopant to replace TBP and Li-TFSI in P3HT HTL in a low temperature (<;1500 C) solgel ZnO ETL processed Methyl Ammonium Lead Triiodide Perovskite solar cell. F4TCNQ doped P3HT HTL devices have shown over two times higher power conversion efficiency compared to pristine P3HT HTL devices. To comprehend the performance enhancement with F4TCNQ dopant in P3HT, we have examined the optical and electronic properties of both the pristine and F4TCNQ doped P3HT devices. Absorbance of Perovskite film lying underneath the undoped and the F4TCNQ doped P3HT film has been investigated to understand superior optical property of F4TCNQ incorporated film. Mott Schottky analysis has been conducted to enunciate the enhanced electronic property with F4TCNQ dopant in P3HT HTL compared to pristine P3HT.