In order to achieve the highest performance of organometal trihalide perovskite solar cells, it is required to recognize the dominant mechanisms which play a key role in a perovskite material. In the ...following studies, we have focused on the interfacial recombination between the hole transporting layer (HTL) and the perovskite CH3NH3PbI3 in solar cell devices with p–i–n architecture. It has been shown that Cu:NiOx used as HTL drastically decreases a short–circuit photocurrent (Jsc) and an open–circuit voltage (Voc). However, we have found that an addition of PTAA thin layer improves cells quality and, as a consequence, the efficiency of such solar cells increases by 2%. Here, we explain both Jsc and Voc losses with a theory of the “dead layer” of perovskite material where a very high surface recombination occurs. We demonstrate the numerical and experimental studies by the means of series detailed analyses to get in–depth understanding of the physical processes behind it. Using a drift–diffusion model, it is shown that the presence of a parasitic recombination layer influences mostly the current distribution in the simulated samples explaining Jsc and Voc losses. The following results could be useful for improving the quality of perovskite solar cells.
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•Interfacial recombination with the theory of the “dead layer” is studied.•Very high surface recombination in the dead layer leads to the Voc and Jsc losses.•Passivation with PTAA thin layer reduces the surface recombination and increases the efficiency of such solar cells by about 2%.•The electrical drift–diffusion model is used to prove the concept of recombination layer.
To improve the power conversion efficiency of solar cells based on organo-lead halide perovskites, a detailed understanding of the device physics is fundamental. Here, a computational analysis of ...excitons impact is reported for these types of photocell. Numerical calculations based on the model, which take into account electronic charge carriers (electrons and holes), excitons and ions, have been carried out. The role of excitons in two crystallographic phases associated with different temperatures (80 K and 295 K) have been studied with the Saha relation, which clearly distinguishes a domination of free charge carriers or excitons. We have confirmed that excitons prevail in the orthorombic phase. Our work provides information about the photophysics of the lead halide perovskite, which allows for a better understanding of the operation of devices based on perovskite materials.
Organometal trihalide perovskites have recently gained extreme attention due to their high solar energy conversion in photovoltaic cells. Here, we investigate the contribution of iodide ions to a ...total conductivity of the mixed lead halide perovskite CH3NH3PbI3−xClx with a use of the modified DC Hebb–Wagner polarization method. It has been identified that an ionic conductivity dominates in tetragonal phase which is associated with room temperature. The obtained activation energy for this type of hopping mechanism is equal to (0.87 ± 0.02) eV, which is in a good agreement with previous literature reports. The high contribution of ionic conductivity at room temperature might be a reason of the observed hysteresis in halide perovskite solar cells.
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•The partial conductivities have been measured in organometal trihalide perovskite (CH3NH3PbI3-xClx).•The domination of ionic conductivity is observed at room temperature.•The activation energy for thermally activated hopping mechanism of iodide ions is (0.87 ± 0.02) eV.•The obtained results might explain the hysteresis in perovskite solar cells.
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•The analysis of excitons annihilation on charge carriers in organic solar cells is presented.•We discuss the influence of excitons interaction with electrons and holes on ...photovoltaic parameters.•The annihilation process leads to lower efficiencies of organic photocells.
We report on theoretical analysis of excitons annihilation on charge carriers in organic solar cells. Numerical calculations based on transient one-dimensional drift-diffusion model have been carried out. An impact of three quantities (an annihilation rate constant, an exciton mobility and a recombination reduction factor) on current density and concentrations of charge carriers and excitons is investigated. Finally, we discuss the influence of excitons interaction with electrons and holes on four photovoltaic parameters (a short-circuit current, an open-circuit voltage, a fill factor and a power conversion efficiency). The conclusion is that the annihilation process visibly decreases the efficiency of organic photocells, if the annihilation rate constant is greater than 10-15m3s-1.
An experimental and theoretical investigation is reported to analyze the relation between the structural and absorption properties of CH3NH3PbI3 in the tetragonal phase. More than 3000 geometry ...optimizations were performed to reveal the structural disorder and identify structures with the lowest energies. The electronic structure calculations provide an averaged band gap of 1.674 eV, which is in excellent agreement with the experimental value of about 1.6 eV. The simulations of the absorption spectrum for three representative structures with lowest energy reproduced the absorption shoulders observed in the experimental spectra. These shoulders are assigned to excitations having similar orbital characters and involving transitions between hybridized 6s(Pb)/5p(I) orbitals and 6p(Pb) orbitals. The geometries of the three structures were analyzed and the effects of the inorganic frame and the CH3NH3+ cations on the absorption properties were estimated. It was found that both changes in the inorganic frame and the CH3NH3+ cations orientations impact the absorption spectra, by modifying the transitions energies and intensities. This highlights the role of CH3NH3+ cation in influencing the absorption properties of CH3NH3PbI3 and demonstrates that CH3NH3+ cation is one of the key elements explaining the broad and nearly constant absorption spectrum in the visible range.
A combined theoretical and experimental study is performed to shed light on the nature of the electronic transitions in the absorption spectrum of the hybrid metal–halide perovskite CH3NH3PbI3. The observed absorption shoulders are assigned by the calculations to different groups of p(I)s(Pb)→p(Pb) transitions involving the inorganic frame. Additionally, it is shown that the orientation of the CH3NH3+ cations has a significant impact on the transition energies and intensities, explaining in part the characteristic absorbance of this material.
The number of publications on perovskite solar cells (PSCs) continues to grow exponentially. Although the efficiency of PSCs has exceeded 25.5%, not every research laboratory can reproduce this ...result or even pass the border of 20%. Unfortunately, it is not always clear which dominating mechanism is responsible for the performance drop. Here, a simple method of light intensity analysis of the JV parameters is developed, allowing an understanding of what the mechanisms are that appear in the solar cell and limit device performance. The developed method is supported by the drift‐diffusion model and is aimed at helping in the explanation of parasitic losses from the interface or bulk recombination, series resistance, or shunt resistance in the perovskite solar cell. This method can help not only point toward the dominating of bulk or interface recombination in the devices but also determine which interface is more defective. A detailed and stepwise guidance for such a type of light intensity analysis of JV parameters is provided. The proposed method and the conclusions of this study are supported by a series of case studies, showing the effectiveness of the proposed method on real examples.
Light intensity analysis of photovoltaic parameters is introduced as a simple method, allowing understanding of the dominating mechanisms limiting the device performance in perovskite solar cells. The method is based on the drift‐diffusion model and is aimed at helping in the explanation of parasitic losses from the trap‐assisted recombination or ohmic losses in devices.
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Highly crystalline NiOX usually requires high annealing temperature (>300 °C) which is incompatible with flexible substrate and might consume high amount of energy. Herein, we ...demonstrate a facile emulsion process to synthesize highly crystalline, low temperature deposition (<150 °C) and solution processable NiOx nanoparticles (NPs) as a hole transport layer for the perovskite solar cells (PVSCs). A novel surfactant of tetramethylammonium hydroxide (TMAOH) was used to react with Ni(NO3)2 to form Ni(OH)2 nanoparticles (NPs). The micelles of TMAOH act as a nano-reactor containing OH− anion. The Ni+ cation enters into the nano-reactor to form Ni(OH)2 NPs inside the reactor with controlled particle size. The Ni(OH)2 NPs prepared by emulsion process are further calcined to form NiOX NPs with the particle size of 8.28 ± 2.64 nm (EP-NiOX). The smaller size of EP-NiOX NPs results in a good dispersibility and an excellent stability of NPs suspension, which can be used to fabricate uniform NiOX film without any aggregates. A power conversion efficiency (PCE) of 18.85% can be achieved using this EP-NiOX film, as compared with 16.68% using the NiOX NPs synthesized from the chemical precipitation method (CPM-NiOX). Moreover, a flexible PVSCs with a PCE of 14.28% can be fabricated using the EP-NiOX film. Except for the device performance, the quality of the EP-NiOX film shows a good batch-to-batch uniformity, resulting in an excellent reproducibility of PVSCs. This work has a potential for the development of a large-scale production of PVSCs with a high energy conservation.
An experimental and theoretical study
is reported to investigate
the influence of bromine doping on CH
3
NH
3
Pb(I
1–
x
Br
x
)
3
perovskite for Br compositions ranging from
x
= 0 to
x
= 0.1, in which ...the material remains in
the tetragonal phase. The experimental band gap is deduced from UV–vis
absorption spectroscopy and displays a linear behavior as a function
of bromine concentration. Density functional theory calculations are
performed for five different series of randomly doped structures in
order to simulate the disorder in bromine doping sites. The computations
predict a linear variation of the lattice parameters, supercell volume,
density, band gap, and formation energy in the considered doping range.
The calculated evolution of the band gap as the function of Br doping
is in excellent agreement with the experimental data, provided that
different Br doping configurations are included in the simulations.
The analysis of the structural and electronic properties shows a correlation
between the increase of the band gap and the increased distortion
of the Pb(I
1–
x
Br
x
)
6
octahedrons. Additionally, the simulations suggest
that in CH
3
NH
3
Pb(I
1–
x
Br
x
)
3
bromine doping
is likely to occur at both the equatorial and apical positions of
the octahedrons.
Recent research has shown that perovskite solar cells with a mixed dual A-cation have much better structural stability without loss of efficiency than single cation devices. Mixed cation perovskites ...create a lot of questions about the salts being used for the formation of the best-quality layer. Here, we have investigated three sources of bromide in the perovskite absorption layer, using lead bromide (PbBr2), formamidinium bromide (FABr), and cesium bromide (CsBr). The experimental results have shown better performance for FABr and CsBr sources of bromide in comparison to the regularly used PbBr2. This effect has been explained with the complex species present in the not-annealed perovskite films which changes the defect states during the crystallization of the absorber layer. It has been found with numerical simulations that the observed phenomenon directly impacts the rates of the trap-assisted recombination. The results of this study are one more step forward in understanding the physics behind the crystallization process which is crucial in further improvement of the perovskite solar cells.
An experimental and theoretical investigation is reported to analyze the relation between the structural and absorption properties of CH
NH
PbI
in the tetragonal phase. More than 3000 geometry ...optimizations were performed to reveal the structural disorder and identify structures with the lowest energies. The electronic structure calculations provide an averaged band gap of 1.674 eV, which is in excellent agreement with the experimental value of about 1.6 eV. The simulations of the absorption spectrum for three representative structures with lowest energy reproduced the absorption shoulders observed in the experimental spectra. These shoulders are assigned to excitations having similar orbital characters and involving transitions between hybridized 6s(Pb)/5p(I) orbitals and 6p(Pb) orbitals. The geometries of the three structures were analyzed and the effects of the inorganic frame and the CH
NH
cations on the absorption properties were estimated. It was found that both changes in the inorganic frame and the CH
NH
cations orientations impact the absorption spectra, by modifying the transitions energies and intensities. This highlights the role of CH
NH
cation in influencing the absorption properties of CH
NH
PbI
and demonstrates that CH
NH
cation is one of the key elements explaining the broad and nearly constant absorption spectrum in the visible range.
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