High efficiency and long-term stability are vital for further development of perovskite solar cells (PSCs). PSCs based on cesium lead halide perovskites exhibit better stability but lower power ...conversion efficiencies (PCEs), compared with organic-inorganic hybrid perovskites. Lower PCE is likely associated with trap defects, overgrowth of partial crystals and irreversible phase transition in the films. Here we introduce a strategy to fabricate high-efficiency CsPbBr3-based PSCs by controlling the ratio of CsBr and PbBr2 to form the perovskite derivative phases (CsPb2Br5/Cs4PbBr6) via a vapor growth method. Following post-annealing, the perovskite derivative phases as nucleation sites transform to the pure CsPbBr3 phase accompanied by crystal rearrangements and retard rapid recrystallization of perovskite grains. This growth procedure induced by phase transition not only makes the grain size of perovskite films more uniform, but also lowers the surface potential barrier that existsbetween the crystals and grain boundaries. Owing to the improved film quality, a PCE of 10.91% was achieved for n-i-p structured PSCs with silver electrodes, and a PCE of 9.86% for hole-transport-layer-free devices with carbon electrodes. Moreover, the carbon electrode-based devices exhibited excellent long-term stability and retained 80% of the initial efficiency in ambient air for more than 2000 h without any encapsulation.
We developed a strategy on the basis of phase transition induced (PTI) crystal rearrangement to fabricate inorganic perovskite solar cells with a high PCE of 10.91% and long-term stability. Display omitted
•We developed a strategy based on phase transition induced (PTI) crystal rearrangement.•Uniform grain size, low surface potential barrier and self-passivation in PTI-films.•This strategy enables fabrication of inorganic CsPbBr3 perovskite solar cells.•Such perovskite solar cells show a high PCE of 10.91% and long-term stability
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nickel oxide (NiO
x
) is a promising hole-selective contact to produce efficient inverted p-i-n structured perovskite solar cells (PSCs) due to its high carrier mobility and high transparency. ...However, the light-induced degradation of the NiO
x
-perovskite heterojunction is the main factor limiting its long-term operational lifetime. In this study, we used the time-resolved mass spectrometry technique to clarify the degradation mechanism of the NiO
x
-formamidinium-methylammonium iodide perovskite (a common composition for high-performance PSCs) heterojunction under operational conditions, and observed that (1) oxidation of iodide and generation of free protons under 1-sun illumination, (2) formation of volatile hydrogen cyanide, methyliodide, and ammonia at elevated temperatures, and (3) a condensation reaction between the organic components under a high vapor pressure. To eliminate these multi-step photochemical reactions, we constructed an aprotic trimethylsulfonium bromide (TMSBr) buffer layer at the NiO
x
/perovskite interface, which enables excellent photo-thermal stability, a matched lattice parameter with the perovskite crystal, and robust trap-passivation ability. Inverted PSCs stabilized with the TMSBr buffer layer reached the maximum efficiency of 22.1% and retained 82.8% of the initial value after continuous operation for 2000 hours under AM1.5G light illumination, which translates into a
T
80
lifetime of 2310 hours that is among the highest operational lifetimes for NiO
x
-based PSCs.
This work introduces an aprotic sulfonium buffer layer at the nickel oxide-perovskite heterojunction to eliminate the multi-step photochemical reactions, which leads to inverted perovskite solar cells with long-term operational stability.
Perovskite photovoltaic (PV) technology toward commercialization relies on high power conversion efficiency (PCE), long lifetime, and low-toxicity in addition to development of scalable fabrication ...protocols, optimization of large-area solar module structures, and a positive cost–benefit assessment. Although small-area metal halide perovskite solar cells (PSCs) show PCE up to 24.2%, the efficiency gap between small- and large-area PSC devices is still large. Worldwide research efforts have been directed toward developing scalable fabrication strategies for perovskite solar modules. In this Review, we share our view regarding the current-stage challenges for the fabrication of perovskite solar modules with areas greater than 200 cm2, summarize recent progress in minimizing the efficiency gap, and highlight what strategies warrant further investigation for moving perovskite PV technology toward industrial scale. These strategies include learning from other commercialized thin-film PV technologies, analyzing the current status of perovskite solar modules employing solution- and vapor-based scalable fabrication techniques, and optimizing large-area module designs. Considering cost analysis and operational stability profiles, carbon electrode-based devices are particularly promising.
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IJS, KILJ, NUK, PNG, UL, UM
Atomic force microscopy (AFM) has found its applications in a wide range of research fields. In this review, we show by examples that atomic force microscopy is a powerful technique to investigate ...structural, mechanical and electrical properties of organic films. We start with an introduction of AFM instrumentation highlighting AFM developments that are of direct relevance to organic films. Next, we review AFM studies on organic films according to their preparation methods: self-assembly, the Langmuir–Blodgett technique, solution preparation, and thermal evaporation. In the discussion on self-assembled monolayers, we focus on aspects such as structural evolution, load-induced molecular tilting, annealing, and incorporation of conjugated groups. For solution prepared organic films, we stress annealing-induced structural evolution as well as the effects of phase separation/segregation. We also briefly summarize the progress of AFM investigation on Langmuir–Blodgett films and thermally evaporated organic films. We conclude the review by providing some thoughts for future exploration. In particular, atomic force microscopy combined with ultra-flat coplanar nano-electrodes provides a promising platform to isolate single or a small number of molecular features (e.g. vacancies, defects, grain boundaries) in organic films as well as to identify the role of these features at the nanometer scale.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Stability and scalability have become the two main challenges for perovskite solar cells (PSCs) with the research focus in the field advancing toward commercialization. One of the prerequisites to ...solve these challenges is to develop a cost‐effective, uniform, and high quality electron transport layer that is compatible with stable PSCs. Sputtering deposition is widely employed for large area deposition of high quality thin films in the industry. Here the composition, structure, and electronic properties of room temperature sputtered SnO2 are systematically studied. Ar and O2 are used as the sputtering and reactive gas, respectively, and it is found that a highly oxidizing environment is essential for the formation of high quality SnO2 films. With the optimized structure, SnO2 films with high quality have been prepared. It is demonstrated that PSCs based on the sputtered SnO2 electron transport layer show an efficiency up to 20.2% (stabilized power output of 19.8%) and a T80 operational lifetime of 625 h. Furthermore, the uniform and thin sputtered SnO2 film with high conductivity is promising for large area solar modules, which show efficiencies over 12% with an aperture area of 22.8 cm2 fabricated on 5 × 5 cm2 substrates (geometry fill factor = 91%), and a T80 operational lifetime of 515 h.
Scalable room‐temperature sputtering deposition of the SnO2 electron transport layer (ETL) with reduced gap states is demonstrated. Perovskite solar cells using a SnO2 ETL show an efficiency up to 20.2% and a T80 lifetime of 625 h. Mini‐modules with a 22.8 cm2 aperture area show efficiencies over 12% and a T80 lifetime of 515 h, which indicates the upscalability of our method.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We deposited lead-free CH
3
NH
3
SnBr
3
- organometal halide perovskite films using two vapor deposition-based methods (
i.e.
, co-evaporation and sequential evaporation) using SnBr
2
and CH
3
NH
3
...Br. We obtained comprehensive information about the structural and electronic properties of these Pb-free perovskite films. X-ray diffraction results confirmed the crystalline structure of MASnBr
3
. Using UV-Vis measurements, we determined the optical bandgap of these films to be ∼2.2 eV. On the basis of ultraviolet photoemission spectroscopy results, the work function and ionization energy were measured to be 4.3 and 6.1 eV, respectively. Solar cells employing such a perovskite film in a planar structure were fabricated with various hole transport layers (HTLs) (spiro-OMeTAD, C60, and P3HT). For perovskite films prepared by co-deposition, we obtained solar cell efficiencies ranging from 0.03 to 0.35%. On the other hand, when we used sequential deposition, a higher efficiency up to 1.12% was obtained using P3HT as the HTL. We confirmed that the low efficiency of MASnBr
3
based perovskite solar cells is due to their relatively high resistance and the fast formation of Sn-Br oxide on the top surface by air exposure during fabrication. The sequential deposition method helped avoid such oxidation resulting in higher efficiencies.
Planar CH
3
NH
3
SnBr
3
perovskite solar cells were fabricated
via
vapor deposition with a protection against air exposure achieved by a thick MABr overlayer.
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Increasing the stability of perovskites is essential for their integration in commercial photovoltaic devices. Halide mixing is suggested as a powerful strategy toward stable perovskite materials. ...However, the stabilizing effect of the halides critically depends on their distribution in the mixed compound, a topic that is currently under intense debate. Here we successfully determine the exact location of the I and Cl anions in the CH3NH3PbBr3–y I y and CH3NH3PbBr3–z Cl z mixed halide perovskite lattices and correlate it with the enhanced stability we find for the latter. By combining scanning tunneling microscopy and density functional theory, we predict that, for low ratios, iodine and chlorine incorporation have different effects on the electronic properties and stability of the CH3NH3PbBr3 perovskite material. In addition, we determine the optimal Cl incorporation ratio for stability increase without detrimental band gap modification, providing an important direction for the fabrication of stable perovskite devices. The increased material stability induced by chlorine incorporation is verified by performing photoelectron spectroscopy on a half-cell device architecture. Our findings provide an answer to the current debate on halide incorporation and demonstrate their direct influence on device stability.
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The use of a solid hole transport layer (HTL) was transformational for the recent perovskite solar cell (PSC) revolution in solar energy technology. Often high efficiency PSC devices employ heavily ...doped hole transport materials such as spiro-MeOTAD. Independent of HTL chemistry, lithium-bis-trifluoromethanesulfonyl-imide (LiTFSI) and tert-butylpyridine (TBP) are commonly used as additives in HTL formulations for PSCs. LiTFSI and TBP were originally optimized for dye-sensitized solar cells, where their roles have been extensively studied. However, in the case of PSCs, the function of TBP is not clearly understood. In this study, properties of the HTL composite deposited on flat silicon substrates were systematically measured at several length scales, e.g., macroscopically (profilometry, 4-point probe conductivity, and thermogravimetry-differential thermal analysis), microscopically, and at the nanoscale to investigate film morphology, conductivity, and dopant distribution. Microscopic distributions of spiro-MeOTAD, LiTFSI, and TBP were determined using 2D Fourier transform infrared (FTIR) microscopy and electrostatic atomic force microscopy (EFM). Our findings reveal that the main role of TBP is to prevent phase segregation of LiTFSI and spiro-MeOTAD, resulting in a homogeneous hole transport layer. These properties are critical for charge transport in the HTL bulk film as well as at the perovskite/HTL and HTL/electrode interfaces and for efficient solar cell performance.
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Because of the rapid rise of the efficiency, perovskite solar cells are currently considered as the most promising next‐generation photovoltaic technology. Much effort has been made to improve the ...efficiency and stability of perovskite solar cells. Here, it is demonstrated that the addition of a novel organic cation of 2‐(6‐bromo‐1,3‐dioxo‐1H‐benzodeisoquinolin‐2(3H)‐yl)ethan‐1‐ammonium iodide (2‐NAM), which has strong Lewis acid and base interaction (between CO and Pb) with perovskite, can effectively increase crystalline grain size and reduce charge carrier recombination of the double cation FA0.83MA0.17PbI2.51Br0.49 perovskite film, thus boosting the efficiency from 17.1 ± 0.8% to 18.6 ± 0.9% for the 0.1 cm2 cell and from 15.5 ± 0.5% to 16.5 ± 0.6% for the 1.0 cm2 cell. The champion cell shows efficiencies of 20.0% and 17.6% with active areas of 0.1 and 1.0 cm2, respectively. Moreover, the hysteresis behavior is suppressed and the stability is improved. The result provides a promising route to further elevate efficiency and stability of perovskite solar cells by the fine tuning of triple organic cations.
A new organic additive (2‐NAM) is introduced into the perovskite film. The introduction of this additive boosts the efficiency from 17.1 ± 0.8% to 18.6 ± 0.9% for the 0.1 cm2 area cells and from 15.5 ± 0.5% to 16.5 ± 0.6% for the 1.0 cm2 area cells. Moreover, the hydrophobic nature of this additive effectively reduces the influence from moisture, thus enhancing the solar cell stability.
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