arXiv subjects

Mihaela Florea

Publications and source records attributed to Mihaela Florea.

3 recordsLinked to original sources

arXiv2024

Electron transporting bilayers for perovskite solar cells: spray coating deposition of c-TiO2/m-SnO2-quantum dots

Herein we present a comparative study among different mesoporous electron transporter layers (ETLs), namely nanometric m-TiO2, m-SnO2 and m-SnO2 quantum dots (QDs), deposited by spray coating method. The experimental data correlated with the photovoltaic parameters indicate that the SnO2 mesoporous layer obtained from the spray deposition of the in-house prepared QDs solution is the best candidate between the three used mesoporous ETLs. The use of the in-house prepared SnO2 QDs solution presents smaller agglomerates composed of 3 nm NPs resulting in the formation of a thinner, more uniform, and compact mesoporous ETL, compared with the other two ETL solutions. The formamidinium-methylamonium-potassium (FAMA@10K) perovskite deposited on this m-SnO2 QDs ETL presents a lower RMS, more uniformity and, a higher amount of PbI2. Interestingly, this higher concentration for PbI2 seems to enhance the performance of the perovskite solar cells (PSC), compared to the other two mesoporous ETLs. Our work reveals that SnO2 QDs solution can be easily produced in the laboratory and it is more suited for the deposition of the mesoporous ETL when choosing a FAMA@10K configuration perovskite solar cell with power conversion efficiency (PCE) higher than 10%.

physics.app-ph↗

arXiv2022

Optoelectronic and stability properties of quasi-2D alkylammonium based perovskites

Electronic and stability properties of quasi-2D alkylammonium perovskites are investigated using density functional theory (DFT) calculations and validated experimentally on selected classes of compounds. Our analysis is focused on perovskite structures of formula (A)$_2$(A$'$)$_{n-1}$Pb$_n$X$_{3n+1}$, with large cations A = butyl-, pentyl-, hexylammonium (BA, PA, HXA), small cations A$'$ = methylammonium, formamidinium, ethylammonium, guanidinium (MA,FA,EA,GA) and halogens X = I, Br, Cl. The role of the halogen ions is outlined for the band structure, stability and defect formation energies. Two opposing trends are found for the absorption efficiency versus stability, the latter being assessed with respect to possible degradation mechanisms. Experimental validation is performed on quasi-2D perovskites based on pentylammonium cations, namely: (PA)$_2$PbX$_4$ and (PA)$_2$(MA)Pb$_2$X$_7$, synthesized by antisolvent-assisted vapor crystallization. Structural and optical analysis are inline with the DFT based calculations. In addition, the thermogravimetric analysis shows an enhanced stability of bromide and chloride based compounds, in agreement with the theoretical predictions.

cond-mat.mtrl-sci↗

arXiv2019

The hysteresis-free behavior of perovskite solar cells from the perspective of the measurement conditions

We investigate in how far the hysteresis-free behavior of perovskite solar cells can be reproduced using particular pre-conditioning and measurement conditions. As there are currently more and more reports of perovskite solar cells without J-V hysteresis it is crucial to distinguish between genuine performance improvements and measurement artifacts. We focus on two of the parameters that influence the dynamic J-V scans, namely the bias scan rate and and the bias poling voltage, and point out measurement conditions for achieving a hysteresis-free behavior. In this context we discuss the suitability of defining a hysteresis index (HI) for the characterization of dynamic J-V scans. Using HI, aging effects are also investigated, establishing a potential connection between the sample degradation and the variation of the maximal hysteresis on one hand, and relaxation time scale of the slow process, on the other hand. Pre-poling induced recombinations effects are identified. In addition, our analysis based on sample pre-biasing reveals potential indication regarding two types of slow processes, with two different relaxation time scales, which provides further insight regarding ionic migration.

physics.app-ph↗