Browsing by Author "Snaith, Henry"

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    Impact of indium doping in lead-free (CH3NH3)3Bi2-xInxI9 perovskite photovoltaics for indoor and outdoor light harvesting
    (American Chemical Society , 2024-11-26) Kumar, Ramesh; Liu, Hairui; Nabavi, Seyed Ali; Anyebe, Moses S; Mahesh, Suhas; Snaith, Henry; Bag, Monojit; Jain, Sagar M
    Hybrid halide perovskites (HHPs) have revolutionized the field of solar cells due to their low cost, solution-processable synthesis, and exceptional device performance. Although lead (Pb)-based perovskites are currently the most efficient, their application in indoor photovoltaics and wearable electronics is limited by lead’s toxicity. This has intensified the search for Pb-free alternatives, particularly for use in portable electronic devices. In this study, we utilized a vapor-assisted solution process to systematically engineer the composition of bismuth-based perovskite-inspired materials (PIMs) through indium doping, forming homogeneous and pinhole-free (CH3NH3)3Bi2–xInxI9 (Bi–In) films. These bimetallic Bi–In perovskites exhibit enhanced properties, including high recombination resistance, reduced low-frequency capacitance, lower defect density, and minimal microstrain. Electrochemical impedance spectroscopy (EIS) shows significantly reduced ion migration in Bi–In compositions compared with pure bismuth-based counterparts. The optimized Bi–In-based solar cells achieved a power conversion efficiency (PCE) of 2.5% under outdoor illumination and 5.9% under indoor lighting, showcasing their potential as promising lead-free alternatives for photovoltaic applications.
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    Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals
    (Royal Society of Chemistry, 2017-02) Ng, Tat Ming; Weller, Mark T; Kissling, Gabriela P; Peter, Laurence M; Dale, Philip; Babbe, Finn; De Wild, Jessica; Wenger, Bernard; Snaith, Henry; Lane, David W.
    Single crystals of Cu2ZnSnS4 (CZTS) have been grown by iodine vapor transport with and without addition of NaI. Crystals with tin-rich copper-poor and with zinc-rich copper-poor stoichiometries were obtained. The crystals were characterized by single crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, photocurrent spectroscopy and electroreflectance spectroscopy using electrolyte contacts as well as by spectroscopic ellipsometry, Raman spectroscopy and photoluminescence spectroscopy (PL)/decay. Near-resonance Raman spectra indicate that the CZTS crystals adopt the kesterite structure with near-equilibrium residual disorder. The corrected external quantum efficiency of the p-type crystals measured by photocurrent spectroscopy approaches 100% close to the bandgap energy, indicating efficient carrier collection. The bandgap of the CZTS crystals estimated from the external quantum efficiency spectrum measured using an electrolyte contact was found to be 1.64–1.68 eV. An additional sub-bandgap photocurrent response (Urbach tail) was attributed to sub bandgap defect states. The room temperature PL of the crystals was attributed to radiative recombination via tail states, with lifetimes in the nanosecond range. At high excitation intensities, the PL spectrum also showed evidence of direct band to band transitions at ∼1.6 eV with a shorter decay time. Electrolyte electroreflectance spectra and spectra of the third derivative of the optical dielectric constant in the bandgap region were fitted to two optical transitions at 1.71 and 1.81 eV suggesting a larger valence band splitting than predicted theoretically. The high values of the EER broadening parameters (192 meV) indicate residual disorder consistent with the existence of tail states.