4 research outputs found
Coupled Heterogeneous Nanowire–Nanoplate Planar Transistor Sensors for Giant (>10 V/pH) Nernst Response
We offer a comprehensive theory of pH response of a coupled ISFET sensor to show that the maximum achievable response is given by Δ<i>V</i>/ΔpH = 59 mV/pH × α, where 59 mV/pH is the intrinsic Nernst response and α an amplification factor that depends on the geometrical and electrical properties of the sensor and transducer nodes. While the <i>intrinsic</i> Nernst response of an electrolyte/site-binding interface is fundamental and immutable, we show that by using channels of different materials, areas, and bias conditions, the <i>extrinsic</i> sensor response can be increased dramatically beyond the Nernst limit. We validate the theory by measuring the pH response of a Si nanowire–nanoplate transistor pair that achieves >10 V/pH response and show the potential of the scheme to achieve (asymptotically) the theoretical lower limit of signal-to-noise ratio for a given configuration. We suggest the possibility of an even larger pH response based on recent trends in heterogeneous integration on the Si platform
Enhancing the Efficiency and Stability of Perovskite Solar Cells through Defect Passivation and Controlled Crystal Growth Using Allantoin
In this study, we present a robust
approach that concurrently
manages
crystal growth and defect passivation within the perovskite layer
through the introduction of a small molecule additiveallantoin.
The precise regulation of crystal growth in the presence of allantoin
yields perovskite films characterized by enhanced morphology, larger
grain size, and improved grain orientation. Notably, the carbonyl
and amino groups present in allantoin passivate under-coordinated
Pb2+ and I– defects, respectively, through
molecular interactions. Trap density in the perovskite layer is measured,
and it is 0.39 × 1016 cm–3 for the
allantoin-incorporated device and 0.83 × 1016 cm–3 for the pristine device. This reduction in defects
leads to reduced trap-assisted nonradiative recombination, as confirmed
by the photoluminescence, transient photo voltage, and impedance measurements.
As a result, when these allantoin-incorporated perovskite films are
implemented as the active layer in solar cells, a noteworthy efficiency
enhancement to 20.63% is attained, surpassing the 18.04% of their
pristine counterparts. Furthermore, devices with allantoin exhibit
remarkable operational stability, maintaining 80% of their efficiency
even after 500 h of continuous illumination, whereas the pristine
device degraded to 65% of its initial efficiency in 400 h. Also, allantoin-incorporated
devices exhibited exceptional stability against high humidity and
elevated temperatures
On the Uniqueness of Ideality Factor and Voltage Exponent of Perovskite-Based Solar Cells
Perovskite-based solar cells have
attracted much recent research
interest with efficiency approaching 20%. While various combinations
of material parameters and processing conditions are attempted for
improved performance, there is still a lack of understanding in terms
of the basic device physics and functional parameters that control
the efficiency. Here we show that perovskite-based solar cells have
two universal features: an ideality factor close to two and a space-charge-limited
current regime. Through detailed numerical modeling, we identify the
mechanisms that lead to these universal features. Our model predictions
are supported by experimental results on solar cells fabricated at
five different laboratories using different materials and processing
conditions. Indeed, this work unravels the fundamental operation principle
of perovskite-based solar cells, suggests ways to improve the eventual
performance, and serves as a benchmark to which experimental results
from various laboratories can be compared
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