Ph.D. (Doctor of Philosophy)
Department of Chemistry and Biochemistry
This dissertation comprehensively studies the research on organic-inorganic hybrid perovskite to solve the toxicity issue of perovskite-based solar cells under practical conditions, understand the doping effect on hybrid perovskite materials in optoelectronic applications, and improve the photovoltaic performance of perovskite-based solar cells by composition tailoring. Specifically, an innovative and simple chemical approach was invented for on-device sequestration of toxic Pb leakage caused by severe device damage. To mimic the practical conditions, the sequestration of lead leakage was conducted under cold water, warm water, acid water, dripping water, and water with competitive ions. Crucially, it was found that at least 96% Pb leakage of the encapsulated device under different conditions can be immediately sequestrated while no negative impact can be observed on the power conversion efficiency (PCE) and stability of PSCs under normal operations compared with the pristine counterparts. Moreover, this approach was further promoted by presenting a scotch-tape-like chemical lead-absorbing encapsulation strategy. After exposing the encapsulated devices to outdoor conditions for more than 3 months, the on-device Pb absorbing layer can still sequestrate more than 99.9% Pb leakage soaking in the water and retain this high sequestration efficiency for more than seven days. Most importantly, this strategy by encapsulating PSCs also shows no negative impacts on PCE and stability in terms of photovoltaic performance in contrast with the bare PSCs while this strategy can be directly applied to devices without altering any standard operational procedures for the fabrication of devices. In addition, other than the encapsulation strategies, Sn is utilized to substitute Pb in perovskite as another attempt to mitigate the potential Pb toxicity issues. Perovskite of CH3NH3SnI3 with the dopant of hydroquinone was prepared. In contrast to the untreated CH3NH3SnI3 films, the hydroquinone-doped CH3NH3SnI3 films exhibit not only greatly retarded degradation in ambient dry air, as shown by the time-dependent X-ray diffraction patterns and X-ray photoelectron spectroscopic analysis, but also enhanced photoluminescence stability under continuous illumination of excitation light in ambient, as evidenced by the time-dependent steady-state photoluminescence results. To further investigate the effects of alkali metal ions on the optoelectronic performance and physical properties of perovskite materials, perovskite of HC(NH2)2PbCl3 nanorods were prepared and HC(NH2)2PbCl3-based ultraviolet photodetectors were fabricated. The results showed the photodetectors based on LiCl-assisted solution-grown HC(NH2)2PbCl3 nanowire films exhibit the remarkably enhanced intensity of photocurrents under UV illumination, more than 5 times of increase with respect to that of photodetectors based on pristine HC(NH2)2PbCl3 nanowire films. Surprisingly, the LiCl-promoted UV photodetectors unexpectedly display extraordinary distinguishability against 254-nm and 365-nm UV photons by alternating current (AC) powered light sources with varying intensities. Especially, under UV illumination with AC-powered 254-nm photons, temporally switched photocurrent directions with periodically oscillating amplitudes were observed for LiCl-promoted UV photodetectors. Instead of adding dopants to the perovskite precursor solutions, composition tailoring is another strategy to improve the photovoltaic performance and stability of devices. Hydrogens in the perovskites of our optimized compositions were substituted by deuterium to form Cs0.5FA0.8MA0.15PbI2.55Br0.45 and Cs0.25FA0.75Sn0.5Pb0.5I3. The PSCs based on the deuterated perovskite displayed greatly enhanced device stability, retaining its initial PCE for the perovskite of Cs0.5FA0.8MA0.15PbI2.55Br0.45 based devices after aging at 85 oC for over 150 hours and retaining 90% of its initial PCE for the perovskite of Cs0.25FA0.75Sn0.5Pb0.5I3 based devices after aging at 50 oC and relative humidity of 50% for 550 hours, which are far more than the PCE of the device with pristine Cs0.5FA0.8MA0.15PbI2.55Br0.45 (less than 40% of initial value) and Cs0.25FA0.75Sn0.5Pb0.5I3 (less than 70% of initial value) after ageing in the same corresponding conditions.
Li, Xun, "Fundamental Study of Dopant Effect and toxicity in Perovskite Materials" (2022). Graduate Research Theses & Dissertations. 7368.
Northern Illinois University
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