To
solve the toxic issue for new-generation photovoltaic applications,
tin-based perovskite solar cells are a promising alternative to their
lead counterparts, but they suffer from poor stability because of
their tendency to exhibit tin oxidation. Herein we report a new sequential
method of deposition based on solution processing using hexafluoro-2-propanol
as a solvent to deposit eight bulky ammonium cations on top of the
3D layer to form a 3D/quasi-2D layer to protect the tin perovskite
grains from penetration by moisture. The formation of the 2D layer
was confirmed with grazing-incidence wide-angle X-ray scattering,
scanning electron microscopy, conducive atomic force microscopy, photoluminescence,
and transient absorption spectroscopy measurements. The anilinium
(AN) device showed a remarkable performance with an efficiency of
10.6% and with great stability in ambient air without encapsulation.
The AN device also showed a self-healing effect of performance when
it was subjected to a severe environment under continuous light soaking
in one-sun illumination and thermal stress between 20 and 50 °C
for 10 cycles.
There have been recent reports on the formation of single-halide perovskites, CH3 NH3 PbX3 (X=Cl, Br, I), by means of vapor-assisted solution processing. Herein, the successful formation of mixed-halide perovskites (CH3 NH3 PbI3-x Xx ) by means of a vapor-assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI2 film to CH3 NH3 X (X=I, Br, or Cl) vapor. The prepared perovskite films have uniform surfaces with good coverage, as confirmed by SEM images. The inclusion of chlorine and bromine into the structure leads to a lower temperature and shorter reaction time for optimum perovskite film formation. In the case of CH3 NH3 PbI3-x Clx , the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH3 NH3 PbI3 (with trace Cl) and CH3 NH3 PbCl3 with a ratio of about 2:1. In the case of CH3 NH3 PbI3-x Brx , single-phase CH3 NH3 PbI2 Br is formed in a considerably shorter reaction time than that of CH3 NH3 PbI3 . The mesostructured perovskite solar cells based on CH3 NH3 PbI3 films show the best optimal power conversion efficiency of 13.5 %, whereas for CH3 NH3 PbI3-x Clx and CH3 NH3 PbI3-x Brx the best recorded efficiencies are 11.6 and 10.5 %, respectively.
We report a simple
synthetic approach to grow uniform CH3NH3PbI3 perovskite (PSK) layers free of pinholes
via varied portions of silver iodide (AgI) added to the precursor
solution. XRD/EDS elemental mapping experiments demonstrated nearly
uniform Ag distribution inside the perovskite film. When the 1% AgI-assisted
perovskite films were fabricated into a p-i-n planar device, the photovoltaic
performance was enhanced by ∼30% (PCE increased from 9.5% to
12.0%) relative to the standard cell without added AgI. Measurement
of electronic properties using a hall setup indicated that perovskite
films show p-type character after Ag doping, whereas the film is n-type
without Ag. Transients of photoluminescence of perovskite films with
and without AgI additive deposited on glass, p-type (PEDOT:PSS), and
n-type (TiO2) contact layers were recorded with a time-correlated
single-photon counting (TCSPC) technique. The TCSPC results indicate
that addition of AgI inside perovskite in contact with PEDOT:PSS accelerated
the hole-extraction motion whereas that in contact with TiO2 led to a decelerated electron extraction, in agreement with the
trend observed from the photovoltaic results. The silver cationic
dopant inside the perovskite films had hence an effect of controlling
the morphology to improve photovoltaic performance for devices with
p-i-n configuration.
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