3 research outputs found
Hindered Formation of Photoinactive δ‑FAPbI<sub>3</sub> Phase and Hysteresis-Free Mixed-Cation Planar Heterojunction Perovskite Solar Cells with Enhanced Efficiency via Potassium Incorporation
Organic–inorganic
hybrid lead halide perovskite solar cells
have demonstrated competitive power conversion efficiency over 22%;
nevertheless, critical issues such as unsatisfactory device stability,
serious current–voltage hysteresis, and formation of photo
nonactive perovskite phases are obstacles for commercialization of
this photovoltaics technology. Herein we report a facial yet effective
method to hinder formation of photoinactive δ-FAPbI<sub>3</sub> and hysteresis behavior in planar heterojunction perovskite solar
cells based on K<sub><i>x</i></sub>(MA<sub>0.17</sub>FA<sub>0.83</sub>)<sub>1–<i>x</i></sub>PbI<sub>2.5</sub>Br<sub>0.5</sub> (0≤ <i>x</i> ≤ 0.1) through
incorporation of potassium ions (K<sup>+</sup>). X-ray diffraction
patterns demonstrate formation of photoinactive δ-FAPbI<sub>3</sub> was almost completely suppressed after K<sup>+</sup> incorporation.
Density functional theory calculation shows K<sup>+</sup> prefers
to enter the interstitial sites of perovskite lattice, leading to
chemical environmental change in the crystal structure. Ultrafast
transient absorption spectroscopy has revealed that K<sup>+</sup> incorporation
leads to enhanced carrier lifetime by 50%, which is also confirmed
by reduced trap-assisted recombination of the perovskite solar cells
containing K<sup>+</sup> in photovoltage decay. Ultraviolet photoelectron
spectroscopy illustrates that K<sup>+</sup> incorporation results
in a significant rise of conduction band minimum of the perovskite
material by 130 meV, leading to a more favorable energy alignment
with electron transporting material. At the optimal content of 3%
K<sup>+</sup> (molar ratio, relative to the total monovalent cations),
nearly hysteresis-free, enhanced power conversion efficiencies from
15.72% to 17.23% were obtained in this solar cell
Tunable Crystallization and Nucleation of Planar CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> through Solvent-Modified Interdiffusion
A smooth
and compact light absorption perovskite layer is a highly desirable
prerequisite for efficient planar perovskite solar cells. However,
the rapid reaction between CH<sub>3</sub>NH<sub>3</sub>I methylammonium
iodide (MAI) and PbI<sub>2</sub> often leads to an inconsistent CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> crystal nucleation and growth
rate along the film depth during the two-step sequential deposition
process. Herein, a facile solvent additive strategy is reported to
retard the crystallization kinetics of perovskite formation and accelerate
the MAI diffusion across the PbI<sub>2</sub> layer. It was found that
the ultrasmooth perovskite thin film with narrow crystallite size
variation can be achieved by introducing favorable solvent additives
into the MAI solution. The effects of dimethylformamide, dimethyl
sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether
additives on the morphological properties and cross-sectional crystallite
size distribution were investigated using atomic force microscopy,
X-ray diffraction, and scanning electron microscopy. Furthermore,
the light absorption and band structure of the as-prepared CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films were investigated and
correlated with the photovoltaic performance of the equivalent solar
cell devices. Details of perovskite nucleation and crystal growth
processes are presented, which opens new avenues for the fabrication
of more efficient planar solar cell devices with these ultrasmooth
perovskite layers
The Influence of the Work Function of Hybrid Carbon Electrodes on Printable Mesoscopic Perovskite Solar Cells
In
printable mesoscopic perovskite solar cells (PSCs), carbon electrodes
play a significant role in charge extraction and transport, influencing
the overall device performance. The work function and electrical conductivity
of the carbon electrodes mainly affect the open-circuit voltage (<i>V</i><sub>OC</sub>) and series resistance (<i>R</i><sub>s</sub>) of the device. In this paper, we propose a hybrid carbon
electrode based on a high-temperature mesoporous carbon (m-C) layer
and a low-temperature highly conductive carbon (c-C) layer. The m-C
layer has a high work function and large surface area and is mainly
responsible for charge extraction. The c-C layer has a high conductivity
and is responsible for charge transport. The work function of the
m-C layer was tuned by adding different amounts of NiO, and at the
same time, the conductivities of the hybrid carbon electrodes were
maintained by the c-C layer. It was supposed that the increase of
the work function of the carbon electrode can enhance the <i>V</i><sub>OC</sub> of printable mesoscopic PSCs. Here, we found
the <i>V</i><sub>OC</sub> of the device based on hybrid
carbon electrodes can be enhanced remarkably when the insulating layer
has a relatively small thickness (500–1000 nm). An optimal
improvement in <i>V</i><sub>OC</sub> of up to 90 mV could
be achieved when the work function of the m-C was increased from 4.94
to 5.04 eV. When the thickness of the insulating layer was increased
to ∼3000 nm, the variation of <i>V</i><sub>OC</sub> as the work function of m-C increased became less distinct