Padinhare Cholakkal Harikesh

Bio: Padinhare Cholakkal Harikesh is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Perovskite (structure) & Neuromorphic engineering. The author has an hindex of 12, co-authored 24 publications receiving 511 citations. Previous affiliations of Padinhare Cholakkal Harikesh include Alagappa University.

Extended Absorption Window and Improved Stability of Cesium-Based Triple-Cation Perovskite Solar Cells Passivated with Perfluorinated Organics

Abstract: Despite the high-quality films achieved with triple-cation perovskites, the deviation from an optimized band gap by virtue of Shockley–Queisser estimation signifies consequential light absorption losses in this system. Herein, it is shown that, by passivating the perovskite surface with a hydrophobic fluorinated organic salt, namely, pentafluoropropylamonium iodide (PFPAI), not only is the band gap narrowed but the process also contributes toward the modulation of surface and electronic properties of the resulting film. The cumulative effect of these factors promotes the enhancement in the power conversion efficiency (PCE) and moisture stability of the perovskite solar cells (PSCs) fabricated with the PFPAI-passivated films. Suppression of surface defects and mitigation of interfacial charge recombination in the treated film are in good agreement with the longer photoluminescence (PL) decay lifetime observed. The PFPAI-passivated PSC afforded a PCE of 16.6% with good ambient stability, evidenced by minima...

Stabilizing the Electroluminescence of Halide Perovskites with Potassium Passivation

Abstract: Halide perovskites are of great interest for light-emitting diodes (PeLEDs) in recent years due to their excellent photo- and electroluminescence properties. However, trap/defects and ion migration...

Realizing reduced imperfections via quantum dots interdiffusion in high efficiency perovskite solar cells

Abstract: Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic-inorganic halide perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid-state interdiffusion process using multi-cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid-state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs+ distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs0.05 (MA0.17 FA0.83 )0.95 PbBr3 (abbreviated as QDs-Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.

Improved photovoltaic performance of triple-cation mixed-halide perovskite solar cells with binary trivalent metals incorporated into the titanium dioxide electron transport layer

Abstract: Among the next-generation photovoltaic technologies, perovskite solar cells have attracted significant attention and interest. In addition to the perovskite absorber component, the adjacent layers within the stack play decisive roles in the stability and overall power conversion efficiency (PCE) of a device. In this study, we demonstrated the use of a solution-processed aluminium indium (AlIn)-TiO2 compact layer as a highly effective electron transport layer (ETL) to achieve outstanding performance of perovskite solar cells; our results showed that the incorporation of AlIn into the TiO2 layer allowed better energy band alignment of the ETL-perovskite interface, improved the transparency, and enhanced the conductivity as compared to the case of pristine TiO2. Via co-doping these trivalent metals, an enhancement in voltage, current density, and even fill factor was observed. In addition, the results obtained from electrochemical impedance spectroscopy (EIS) revealed that the AlIn-TiO2-based device exhibited larger recombination resistance, which significantly benefited the performance of the devices. As a result, the optimized AlIn-TiO2 ETL device attained the surpassing PCE of 19% as compared to the pristine TiO2 solar device having the PCE of 16.67%.

Cubic NaSbS2 as an Ionic-Electronic Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications.

Abstract: The recent emergence of lead halide perovskites as ionic-electronic coupled semiconductors motivates the investigation of alternative solution-processable materials with similar modulatable ionic and electronic transport properties. Here, a novel semiconductor-cubic NaSbS2 -for ionic-electronic coupled transport is investigated through a combined theoretical and experimental approach. The material exhibits mixed ionic-electronic conductivity in inert atmosphere and superionic conductivity in humid air. It is shown that post deposition electronic reconfigurability in this material enabled by an electric field induces ionic segregation enabling a switchable photovoltaic effect. Utilizing post-perturbation of the ionic composition of the material via electrical biasing and persistent photoconductivity, multistate memristive synapses with higher-order weight modulations are realized for neuromorphic computing, opening up novel applications with such ionic-electronic coupled materials.

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Abstract: The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Toward Lead-Free Perovskite Solar Cells

Abstract: Since the first reports of solar cells with power conversion efficiencies around 10% in 2012, the science and technology of perovskite photovoltaics has been progressing at an unprecedented rate. The current certified record efficiency of 22.1% makes perovskites the first solution-processable technology to outperform multicrystalline and thin-film silicon. For this technology to be deployed on a large scale, the two main challenges that need to be addressed are the material stability and the toxicity of lead. In particular, while lead is allowed in photovoltaic modules, it would be desirable to find alternatives which retain the unique optoelectronic properties of lead halide perovskites. Here we offer our perspective on the most exciting developments in the materials science of new halide perovskites, with an emphasis on alternatives to lead. After surveying recent developments of new perovskites and perovskite-related materials, we highlight the potential of halide double perovskites. This new family of...

Lead-Free Organic-Inorganic Hybrid Perovskites for Photovoltaic Applications: Recent Advances and Perspectives.

Abstract: Organic-inorganic hybrid halide perovskites (e.g., MAPbI3 ) have recently emerged as novel active materials for photovoltaic applications with power conversion efficiency over 22%. Conventional perovskite solar cells (PSCs); however, suffer the issue that lead is toxic to the environment and organisms for a long time and is hard to excrete from the body. Therefore, it is imperative to find environmentally-friendly metal ions to replace lead for the further development of PSCs. Previous work has demonstrated that Sn, Ge, Cu, Bi, and Sb ions could be used as alternative ions in perovskite configurations to form a new environmentally-friendly lead-free perovskite structure. Here, we review recent progress on lead-free PSCs in terms of the theoretical insight and experimental explorations of the crystal structure of lead-free perovskite, thin film deposition, and device performance. We also discuss the importance of obtaining further understanding of the fundamental properties of lead-free hybrid perovskites, especially those related to photophysics.

Cs$_2$InAgCl$_6$: A new lead-free halide double perovskite with direct band gap

Abstract: A$_2$BB$^\prime$X$_6$ halide double perovskites based on bismuth and silver have recently been proposed as potential environmentally-friendly alternatives to lead-based hybrid halide perovskites. In particular, Cs$_2$BiAgX$_6$ (X = Cl, Br) have been synthesized and found to exhibit band gaps in the visible range. However, the band gaps of these compounds are indirect, which is not ideal for applications in thin film photovoltaics. Here, we propose a new class of halide double perovskites, where the B$^{3+}$ and B$^{+}$ cations are In$^{3+}$ and Ag$^{+}$, respectively. Our first-principles calculations indicate that the hypothetical compounds Cs$_2$InAgX$_6$ (X = Cl, Br, I) should exhibit direct band gaps between the visible (I) and the ultraviolet (Cl). Based on these predictions, we attempt to synthesize Cs$_2$InAgCl$_6$ and Cs$_2$InAgBr$_6$, and we succeed to form the hitherto unknown double perovskite Cs$_2$InAgCl$_6$. X-ray diffraction yields a double perovskite structure with space group $Fm\overline{3}m$. The measured band gap is 3.3 eV, and the compound is found to be photosensitive and turns reversibly from white to orange under ultraviolet illumination. We also perform an empirical analysis of the stability of Cs$_2$InAgX$_6$ and their mixed halides based on Goldschmidt's rules, and we find that it should also be possible to form Cs$_2$InAg(Cl$_{1-x}$Br$_{x}$)$_6$ for $x<1$. The synthesis of mixed halides will open the way to the development of lead-free double perovskites with direct and tunable band gaps.

From Lead Halide Perovskites to Lead-Free Metal Halide Perovskites and Perovskite Derivatives

Abstract: Despite the exciting progress on power conversion efficiencies, the commercialization of the emerging lead (Pb) halide perovskite solar cell technology still faces significant challenges, one of which is the inclusion of toxic Pb. Searching for Pb-free perovskite solar cell absorbers is currently an attractive research direction. The approaches used for and the consequences of Pb replacement are reviewed herein. Reviews on the theoretical understanding of the electronic, optical, and defect properties of Pb and Pb-free halide perovskites and perovskite derivatives are provided, as well as the experimental results available in the literature. The theoretical understanding explains well why Pb halide perovskites exhibit superior photovoltaic properties, but Pb-free perovskites and perovskite derivatives do not.