8 research outputs found
Predictive modeling of ion migration induced degradation in perovskite solar cells
With excellent efficiencies being reported from multiple labs across the
world, device stability and the degradation mechanisms have emerged as the key
aspects that could determine the future prospects of perovskite solar cells.
However, the related experimental efforts remain scattered due to the lack of
any unifying theoretical framework. In this context, here we provide a
comprehensive analysis of ion migration effects in perovskite solar cells.
Specifically, we show, for the first time, that (a) the effect of ionic charges
is almost indistinguishable from that of dopant ions, (b) ion migration could
lead to simultaneous improvement in Voc and degradation in Jsc - a unique
observation which is beyond the realm of mere parametric variation in carrier
mobility and lifetime, (c) champion devices are more resilient towards the ill
effects of ion migration, and finally (d) we propose unique characterization
schemes to determine both magnitude and polarity of ionic species. Our results,
supported by detailed numerical simulations and direct comparison with
experimental data, are of broad interest and provide a much needed predictive
capability towards the research on performance degradation mechanisms in
perovskite solar cellsComment: 8 pages, 5 figure
Unveiling charge dynamics of visible light absorbing oxysulfide for efficient overall water splitting
Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and therefore, imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement. Herein, transient diffuse reflectance spectroscopy measurements are coupled with theoretical calculations to unveil the nanosecond to microsecond time range dynamics of the photogenerated charge carriers. In early nanosecond range, the pump-fluence-dependent decay dynamics of the absorption signal is originated from the bimolecular recombination of mobile charge carriers, in contrast, the power-law decay kinetics in late microsecond range is dominated by hole detrapping from exponential tail trap states of valence band. A well-calibrated theoretical model estimates various efficiency limiting material parameters like recombination rate constant, n-type doping density and tail-states parameters. Compared to metal oxides, longer effective carrier lifetime ~6 ns is demonstrated. Different design routes are proposed to realize efficiency beyond 10% for commercial solar-to-hydrogen production from oxysulfide photocatalysts
Unveiling charge dynamics of visible light absorbing oxysulfide for efficient overall water splitting
Elucidating the Role of Surface Energetics on Charge Separation during Photoelectrochemical Water Splitting
Efficient photoelectrochemical (PEC) water splitting
requires charge
separation and extraction from a photoactive semiconductor. Such a
charge transport process is widely believed to be dictated by the
bulk energetics of the semiconductor. However, its dependence on surface
energetics along the semiconductor/electrolyte interface remains an
open question. Here, we elucidate the influence of surface energetics
on the performance of a well-established Mo-doped BiVO4 photoanode whose surface energetics are regulated by the facet-selective
cocatalyst loading. Surprisingly, photodeposition of RhOx and CoOx cocatalysts
onto the {010} and {110} facets, respectively, strongly enhanced the
charge-separation efficiency, in addition to improving the injection
efficiency for water oxidation. Detailed optoelectrical simulations
confirm that the synergistic enhancement of charge separation originates
from the distinct effects of the cocatalyst loading on the surface
energetics. This insight into the fundamental charge-separation mechanism
in PEC cells provides a perspective for cell design and operation
Efficient Organic Photovoltaics with Improved Charge Extraction and High Short-Circuit Current
Exciton
generation, dissociation, free carrier transport, and charge
extraction play an important role in the short-circuit current (<i>J</i><sub>sc</sub>) and power conversion efficiency of an organic
bulk heterojunction (BHJ) solar cell (SC). Here we study the impact
of band offset at the interfacial layer and the morphology of active
layer on the extraction of free carriers. The effects are evaluated
on an inverted BHJ SC using zinc oxide (ZnO) as a buffer layer, prepared
via two different methods: ZnO nanoparticle dispersed in mixed solvents
(ZnO A) and sol–gel method (ZnO B). The device with ZnO A buffer
layer improves the charge extraction and <i>J</i><sub>sc</sub>. The improvement is due to the better band offset and morphology
of the blend near the ZnO A/active layer interface. Further, the numerical
analysis of current–voltage characteristics illustrates that
the morphology at the ZnO A/active layer interface has a more dominant
role in improving the performance of the organic photovoltaic than
the band offset