Long-term stability of organic-inorganic metal halide perovskite solar cells (PSCs) is a prerequisite for their successful commercialization. Electrode failure is one of the most critical reasons for the degradation of perovskite solar cells during aging test. The electrode failure is dominantly due to corrosion of metal contacts by the iodine ion migrated from the perovskite active layer. To conquer the instability of PSCs, we inserted a compact ultra-thin Al2O3 interlayer between electron transfer layer and metal contact by atomic layer deposition (ALD) processed at 65℃. Experimental results show that 8 deposition cycle ALD Al2O3 thin film (~2 nm) improve the efficiency as well as the stability of the PSCs. It is found that the Al2O3 layer plays an important role of blocking iodide ion migration, preventing moisture and oxygen penetration and improving the efficiency of electron extraction. Statistically, the perovskite solar cells achieve a power conversion efficiency (PCE) of 19.50% (Voc of 1.061 V, and Jsc of 23.03 mA/cm2), and remain 80% of its initial performance after 1200 hours of storage in ambient air condition, also remained 97.4% of its initial performance when heated at 85℃ for 48 hours. Compared to the devices without ALD Al2O3 interlayer, the PCE is improved 12%, and the stability is extended for 400 hrs. This work highlights the importance of introducing ultra-thin compact ion blocking layer to the high performance perovskite solar cell devices.
Inorganic–organic hybrid perovskites have received extensive attention in the field of optoelectronic devices, due to its lower cost, high carrier mobility, high defect tolerance, narrow emission bandwidth and tunable emission spectra. In recent years, we have observed a rapid development of perovskite based light emitting diodes (LED), however, the performance of blue perovskite LED falls far behind the green and red LEDs. The blue perovskite LED suffers from the fast crystallization of chlorine based perovskite, and the instability of the mixture phase of chlorine and bromine under electrical stress. In this work, in order to improve the stability of blue LED, the macro-molecular material butylammonium chlorine (BACl) is introduced into three-dimensional cesium lead bromide (CsPbBr3) to form quasi two-dimensional perovskite structure. By adjusting the molar ratio of BACl over CsPbBr3, the number of inorganic layers (n) in the quasi-two-dimensional structure is finely tuned. A color stable perovskite light emitting diodes with wavelength ranging from 450-490nm (deep blue to sky blue) is achieved. Furthermore, phenethylammonium (PEA) cation, a water and oxygen stable aromatic material, is added into the quasi 2D perovskite precursor to form mixed spacer cation perovskite layer. The performance and stability of the blue LED with different molar proportion of BA+ to PEA+ is investigated. Finally, a color stable perovskite blue LED with luminance exceeding 1000 Cd/m2 is achieved.
Nonstoichiometric nickel oxide (NiOx) hole transport layer (HTL) plays an important role in realizing high efficient and hysteresis-free perovskite solar cells (PSCs). Here, we report a precursor additive approach for forming high-quality solution processed NiOx interlayer. A small quantity of reduced graphene oxide (rGO) is added to the conventional NiOx precursor. It is found that the modified precursor lead to an improved hole extraction efficiency and uniformity of the NiOx thin film. Statistically, compared to non-modified NiOx precursor, perovskite solar cells based on NiOx:rGO precursor have higher short-circuit current densities (Jsc) and higher fill factors (FF).
Nanowires (NW)/nanopillars (NP) have unique optical and electrical properties that make them attractive for
photovoltaic applications. Important factors such as diameter, length and array density of the nanowires have
investigated in the recent years or their effect on light trapping. In this work, we study the effect of varying
the NWs top tip morphology, and find significant differences in optical response, both via simulations and
experiments. In the simulations, optical performance of NW with flat top and spherical top were investigated.
The simulated 3D model is a CNT/Cr/a-Si/ITO coaxial structure with total diameter of 760nm. Our results
show that as the spacing of the NWgets smaller, the influence of the top morphology on the nanowires’ reflectance
becomes more significant. For narrow spacing arrays (p<2d, where p is the period and d is the diameter of NWs)
NW device with spherical top shows better antireflection performance than the one with flat top. This is due to
the biomimetic antireflection (AR) effect introduced by the spherical top . For large spacing arrays (p<2d), AR
effect introduced by spherical tops was almost negligible. It can be ascribed to the low volume concentration
of the spherical top comparing to that of the planar surface. In addition, effect of structural defects were also
Minimizing surface reflection loss is critical when designing high efficiency solar cells. In recent years, biomimetic
antireflection nanostructures (such as moth-eye structures), with their extraordinary broadband and omnidirectional
antireflection properties, have caught much attention. Single side biomimetic antireflection (AR) coatings
show good performance in suppressing broadband reflection between air and glass interface. However, reflection
from the interface between absorption layer and transparent window layer still remains. In this study,
we proposed a double-side gradient-index nanostructure, and examined its reflection spectrum in comparison
with different biomimetic nanostructures using a finite-difference time-domain (FDTD) simulation and effective
medium theory (EMT). In order to minimize surface reflection, all abrupt interfaces were replaced by gradientindex
biomimetic nanostructures, including air/glass interface and absorber/glass interface. Monolayer of silica
spheres serve as double-side gradient-index nanostructures, partially immersed into photoabsorbing material.
Spheres with diameter smaller than incoming light wavelength show excellent antireflection properties. From
simulation results, in normal incidence, average reflection rate of optimized AR coating structure was lower to
around 5% compared to originally above 25% within visible spectrum region (350nm – 850nm). Details of how
to apply such biomimetic nanostructures in thin film solar cells were also discussed.
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