Sabba Dharani

Bio: Sabba Dharani is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Perovskite (structure) & Solar cell. The author has an hindex of 5, co-authored 5 publications receiving 1448 citations.

Lead‐Free Halide Perovskite Solar Cells with High Photocurrents Realized Through Vacancy Modulation

Abstract: Lead free perovskite solar cells based on a CsSnI3 light absorber with a spectral response from 950 nm is demonstrated. The high photocurrents noted in the system are a consequence of SnF2 addition which reduces defect concentrations and hence the background charge carrier density.

High efficiency electrospun TiO2 nanofiber based hybrid organic–inorganic perovskite solar cell

Abstract: The good electrical and morphological characteristics of TiO₂ nanofibers and the high extinction coefficient of CH₃NH₃PbI₃ perovskite are combined to obtain a solar cell with a power conversion efficiency of 9.8%. The increase of the film thickness dramatically diminishes the performance due to the reduction in porosity of the TiO₂ nanofiber framework. The optimum device (∼413 nm film thickness) is compared to a planar device, where the latter produces higher V(oc) but lower J(sc), and consequently lower efficiency at all measured light intensities.

Incorporation of Cl into sequentially deposited lead halide perovskite films for highly efficient mesoporous solar cells

Abstract: Organic–inorganic lead halide perovskites have been widely used as absorbers on mesoporous TiO2 films as well as thin films in planar heterojunction solar cells, yielding very high photovoltaic conversion efficiencies. Both the addition of chloride and sequential deposition methods were successfully employed to enhance the photovoltaic performance. Here, both approaches are combined in a sequential method by spincoating PbCl2 + PbI2 on a mesoporous TiO2 film followed by the perovskite transformation. The role of Cl in determining the optical, electrical, structural and morphological properties is correlated with the photovoltaic performance. The highest photovoltaic efficiency of 14.15% with the Voc, FF and Jsc being 1.09 V, 0.65 and 19.91 mA cm−2 respectively was achieved with 10 mol% of PbCl2 addition due to an increase of the film conductivity induced by a better perovskite morphology. This is linked to an improvement of the hysteresis and reproducibility of the solar cells.

Cobalt Dopant with Deep Redox Potential for Organometal Halide Hybrid Solar Cells

Abstract: In this work, we report a new cobalt(III) complex, tris[2-(1H-pyrazol-1-yl)pyrimidine]cobalt(III) tris[bis(trifluoromethylsulfonyl)imide] (MY11), with deep redox potential (1.27 V vs NHE) as dopant for 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). This dopant possesses, to the best of our knowledge, the deepest redox potential among all cobalt-based dopants used in solar cell applications, allowing it to dope a wide range of hole-conductors. We demonstrate the tuning of redox potential of the Co dopant by incorporating pyrimidine moiety in the ligand. We characterize the optical and electrochemical properties of the newly synthesized dopant and show impressive spiro-to-spiro(+) conversion. Lastly, we fabricate high efficiency perovskite-based solar cells using MY11 as dopant for molecular hole-conductor, spiro-OMeTAD, to reveal the impact of this dopant in photovoltaic performance. An overall power conversion efficiency of 12% is achieved using MY11 as p-type dopant to spiro-OMeTAD.

Low-temperature solution-processed wavelength-tunable perovskites for lasing

Abstract: Low-temperature solution-processed materials that show optical gain and can be embedded into a wide range of cavity resonators are attractive for the realization of on-chip coherent light sources. Organic semiconductors and colloidal quantum dots are considered the main candidates for this application. However, stumbling blocks in organic lasing include intrinsic losses from bimolecular annihilation and the conflicting requirements of high charge carrier mobility and large stimulated emission; whereas challenges pertaining to Auger losses and charge transport in quantum dots still remain. Herein, we reveal that solution-processed organic-inorganic halide perovskites (CH 3 NH 3 PbX 3 where X = Cl, Br, I), which demonstrated huge potential in photovoltaics, also have promising optical gain. Their ultra-stable amplified spontaneous emission at strikingly low thresholds stems from their large absorption coefficients, ultralow bulk defect densities and slow Auger recombination. Straightforward visible spectral tunability (390-790 nm) is demonstrated. Importantly, in view of their balanced ambipolar charge transport characteristics, these materials may show electrically driven lasing. © 2014 Macmillan Publishers Limited.

Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques

Abstract: The use of a thin layer of zinc oxide nanoparticles as an electron-transport layer allows flexible perovskite solar cells to be fabricated with a power conversion efficiency as high as 15.7%.

Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorber

Abstract: Thin-film solar cells based on Methylammonium triiodideplumbate (CH3NH3PbI3) halide perovskites have recently shown remarkable performance First-principle calculations show that CH3NH3PbI3 has unusual defect physics: (i) Different from common p-type thin-film solar cell absorbers, it exhibits flexible conductivity from good p-type, intrinsic to good n-type depending on the growth conditions; (ii) Dominant intrinsic defects create only shallow levels, which partially explain the long electron-hole diffusion length and high open-circuit voltage in solar cell The unusual defect properties can be attributed to the strong Pb lone-pair s orbital and I p orbital antibonding coupling and the high ionicity of CH3NH3PbI3

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...

Low-Temperature Solution-Processed Perovskite Solar Cells with High Efficiency and Flexibility

Abstract: Perovskite compounds have attracted recently great attention in photovoltaic research. The devices are typically fabricated using condensed or mesoporous TiO2 as the electron transport layer and 2,2′7,7′-tetrakis-(N,N-dip-methoxyphenylamine)9,9′-spirobifluorene as the hole transport layer. However, the high-temperature processing (450 °C) requirement of the TiO2 layer could hinder the widespread adoption of the technology. In this report, we adopted a low-temperature processing technique to attain high-efficiency devices in both rigid and flexible substrates, using device structure substrate/ITO/PEDOT:PSS/CH3NH3PbI3–xClx/PCBM/Al, where PEDOT:PSS and PCBM are used as hole and electron transport layers, respectively. Mixed halide perovskite, CH3NH3PbI3–xClx, was used due to its long carrier lifetime and good electrical properties. All of these layers are solution-processed under 120 °C. Based on the proposed device structure, power conversion efficiency (PCE) of 11.5% is obtained in rigid substrates (glass/...