Chen Weijie

An effective strategy to simultaneously obtain high photocurrent and fill factor in tandem organic solar cells is presented. By increasing the proportion of the non-fullerene acceptor with strong absorption in the front sub-cell, maximum photocurrent can be obtained without significantly increasing the thickness of the front sub-cell, thus ensuring a high fill factor and high photocurrent in device, with a power conversion efficiency over 18%.

Abstract

The maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub-cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub-cell in such TOSCs can be reduced by increasing the proportion of a non-fullerene acceptor in the active layer. The non-fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub-cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub-cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine-turning of the composition in the front sub-cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained.

A novel type of releasing nanocapsule is designed and demonstrated for high-throughput printing of highly efficient perovskite solar cells with excellent stability. The releasing effect of these perovskite nanocapsules promotes homogeneous nucleation by diffusion-controlled growth. A record manufacturing efficiency of 140 s is demonstrated for perovskite solar modules installation of 1 kW.

Abstract

Perovskite solar cells (PSCs) are promising photovoltaic technologies due to their impressive power conversion efficiency (PCE) and low-temperature fabrication process, while it is still challenging to print uniform perovskite film with high crystalline quality over a module size. Here, a printable and stable perovskite nanocapsules ink to realize the high-throughput printing of large-area, highly uniform perovskite films with micron grain size is reported. It is discovered that the releasing effect of these perovskite nanocapsules promotes homogeneous nucleation by diffusion-controlled growth due to the steady-state diffusion of the solute in solution. Remarkably, the printed PSCs and 25 cm² modules achieve power conversion efficiencies of 22.10% and 16.12%, respectively. They exhibit negligible efficiency loss after continuous operation for over 1000 h under AM1.5 illumination, and excellent thermal (85 °C) stability with over 87% of the initial efficiency after aging for 500 h. This perovskite nanocapsules ink is expected to facilitate the high-yield fabrication of perovskite photovoltaics.

Efficient pure-blue perovskite light-emitting diodes with external quantum efficiency reaching 10.1% and maximum luminance of 14 000 cd m⁻² are realized by simultaneous incorporation of Rb⁺ and Cl⁻ ions and long-chain ligands into CsPbBr₃. The compositional engineering promotes the formation of quasi-2D perovskites with wide bandgap, and results in sub-micrometer-sized particles on the film surface that enhance the light outcoupling.

Abstract

Perovskite light-emitting diodes (PeLEDs) are promising candidates for display and solid-state lighting, due to their tunable colors, high conversion efficiencies, and low cost. However, the performance of blue PeLEDs is far inferior to that of the near-infrared, red, and green counterparts. Here, the fabrication of pure-blue PeLEDs with an emission peak at 475 nm, a peak external quantum efficiency of 10.1%, and a maximum luminance of 14 000 cd m⁻² is demonstrated by tailoring the compositions of perovskites. The pure-blue electroluminescence is achieved by simultaneous addition of rubidium and chlorine ions into CsPbBr₃ and incorporation of phenylethylammonium chloride forms quasi-2D hybrid perovskites. The combination of these composition engineering results in blueshifted emissions without reducing the quantum yield. The judicious alloying is shown to be critical to result in the better morphology with suppressed current leakage and enhanced light outcoupling.

NiO _x is used as the hole transport layer with the synergistic effect of poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyfluorene)] (PFN) to shift the valence band downward, leading to reduced open circuit voltage (V _oc) loss and improved efficiency. The champion perovskite solar cell has a remarkable V _oc of 0.88 V, surpassing the previous results reported for NiO _x -based Sn-Pb PSCs.

Tin–lead (Sn–Pb) binary low-bandgap perovskites are more environmentally friendly than conventional Pb-based perovskites and promise to deliver high photovoltaic performance by constructing tandem solar cells. However, the energy-level mismatch between functional layers and tremendous trap states in perovskite films make it challenging to reduce the high open-circuit voltage (V _oc) loss in Sn–Pb binary perovskite solar cells (PSCs). Herein, energy loss reduction at the hole collection interface in Sn–Pb binary PSCs is demonstrated using nickel oxide (NiO _x ) as the hole transport material (HTM) with optimal poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyfluorene)] (PFN) modification, which enables a significantly enhanced V _oc compared to the traditional poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)-based devices. The NiO _x /PFN bilayer has a downward-shifted valence band compared to PEDOT:PSS, providing well-matched energy-level alignment with the perovskite material, resulting in more fluent charge transfer and reduced V _oc losses. The optimized device has a high V _oc of 0.88 V and an efficiency of 19.80%, surpassing the previous results reported for NiO _x -based Sn–Pb PSCs. Moreover, the robust NiO _x /PFN substrate and the high-quality perovskite film grown on it make the device less vulnerable to ambient exposure. This work highlights the significance of ideal hole conductors and interface engineering in efficient and stable Sn–Pb low-bandgap PSCs.

One-step slot-die deposition route, combining ink tailoring and vacuum aspiration solvent extraction, is developed for the deposition of a high-bandgap multication perovskite. Implementing this perovskite layer into a solar device, a stabilized power conversion efficiency up to 17.5% and a stability over 180 h under maximum power point conditions in air atmosphere are reached.

Slot-die coating is a promising technique paving the way for large-area perovskite deposition and commercially relevant solar device fabrication with sharp control over the thickness and material composition. However, before transferring perovskite solar cells technology to commercial applications, it is required to develop ink formulations, guaranteeing high homogeneity over a wide surface and leading to large, defect-free, and well-crystallized perovskite grains to maximize the device performances. A one-step slot-die deposition route, combining ink tailoring and vacuum aspiration solvent extraction, affording the deposition of a high-bandgap multication perovskite, is reported. One important key is the introduction of methylammonium chloride in the ink formulation, which substantially enhances the film quality over a large area. Although the efficacy of antisolvent dripping is demonstrated on a small area, it is not compatible with larger areas. This work compares the latter with a vacuum quench protocol, allowing efficient extraction of the solvents. Considering both ink formulation engineering and vacuum solvent extraction, a stabilized power conversion efficiency of up to 17.5% is reached. This constitutes, to the best of our knowledge, the highest reported value for a high-bandgap absorber deposited by slot-die coating. Moreover, stability over 180 h under maximum power point conditions is herein demonstrated.

Au@Cu_2−x S nanoparticles are introduced to modify the perovskite/spiro-OMeTAD interface, enhancing the infrared absorption, intensifying the interface electric-field due to localized surface plasmon resonance, and forming “bridges” between perovskite grains and spiro-OMeTAD to passivate surface traps and smooth the interfaces' valence-band offset for balanced charge transport. Consequently, the corresponding perovskite solar cell achieves a champion efficiency over 22%.

Core–shell nanomaterials have led to their fascinating properties in optical applications due to the localized surface plasmon resonance (LSPR). Herein, a mesoporous core–shell Au@Cu_2−x S nanomaterial with dual LSPR characteristics is introduced to stabilize and passivate the perovskite/spiro-OMeTAD interface of perovskite solar cells (PSCs). Thanks to the LSPR, Au@Cu_2−x S nanoparticles (NPs) have the potential to enhance the infrared absorption and intensify the local electric field at the perovskite/spiro-OMeTAD interface. The embedding of the mesoporous Au@Cu_2−x S in the spiro-OMeTAD layer can improve the contact and form “bridges” between perovskite grains and spiro-OMeTAD. With the help of cationic surfactant cetyltrimethylammonium bromide, these mesoporous Au@Cu_2−x S NPs can passivate surface traps and smooth the valence-band offset at the perovskite/spiro-OMeTAD interface for hole transferring. Furthermore, the improved hole mobility can offer balanced charge transport and prevent the carrier accumulation at interfaces. As a result, the Au@Cu_2−x S(20:10)-based PSCs achieves a champion efficiency over 22%, higher than that of the Au@Cu_2−x S-based device.

Potential-induced degradation (PID) is known as a common reliable threat in the established commercial PV technologies which lead to catastrophic failure within a short time. To reveal the PID impact and degradation mechanism in the early-stage development of upcoming commercial technology, different architecture-based perovskite solar cells are investigated under PID.

Organic–inorganic perovskites photovoltaic materials are considered as one of the promising candidates for the emerging photovoltaic (PV) sector. It has drawn tremendous attention from fundamental research and PV industries, due to its high efficiency, chemical properties, and low fabrication cost. But, its lifetime under real field operation is always the major obstacle toward commercialization. Potential-induced degradation (PID) is known as the common reliable threat in the established commercial PV technologies which lead to catastrophic failure within a short time. Thus, it is essential to enable reliability assessment of PID on the precommercial development stage of perovskite photovoltaics to further enrich the confidence by identifying, eliminating, and developing an understanding of the possible degradation mechanism in the field condition. In this article, different architecture-based perovskite solar cells are studied to reveal the degradation mechanism under PID for the first time. The results show that PSCs of n–i–p with a phenyl C61 butyric acid methyl ester (PCBM) layer have good stability under PID compared with other treated structures with only 4% degradation after 18 h.

The moisture instability of perovskite solar cells is addressed using an inner encapsulating technology that uses a metal adhesive layer for the formation of a compact metal electrode, which can effectively stop the penetration of moisture into the adjacent layer and perovskite materials, resulting in a moisture-resilient perovskite solar cell without additional encapsulation.

The degradation of the perovskite layer in atmospheric air is a critical bottleneck for the commercialization of perovskite solar cells (PSCs). As the moisture and oxygen in air penetrate the charge transport layer/top metal electrode interface, both adjacent layers and perovskite layers decompose in the PSCs. Herein, moisture-stable inverted PSCs (I-PSCs) based on methylammonium lead triiodide (MAPbI₃) by introducing amine-functionalized small molecules as metal adhesive layers (MALs) between the electron transport layer (ETL) and metal electrode (here, Cu) are demonstrated. A strong coordination bond of CuN forms at the Cu/MAL interface, leading to the layer–layer growth mode for the dense formation of Cu electrodes with a strong adhesion to the ETL. Thus, this modified electrode prevents the ingress of moisture into the I-PSCs, resulting in outstanding moisture stability; the efficiency of I-PSCs retains 90% of the initial efficiency after 200 days of exposure to atmospheric air (25 °C, relative humidity [RH] ≈20–40%). Under harsher conditions (e.g., 25 °C/RH65%, 25 °C/RH85% and immersion in water) for a considerable time period, the modified I-PSCs manifest relatively no degradation compared with the pristine I-PSCs. It is believed that this breakthrough provides a significant impact on improving the stability of I-PSCs.

BMIMBF₄ is used to improve the CsPbI₂Br/carbon interface. It not only passivates perovskite surface defects but also reduces the energy-level mismatch between perovskite and carbon. The stability of devices and films is also improved through BMIMBF₄ modification, resulting in an improved efficiency (from 11.37% to 14.03%), featuring a V _OC of 1.27 V.

Carbon-based hole transport material (HTM)-free CsPbI₂Br perovskite solar cells (C-PSCs) have garnered considerable attention due to their super thermal stability. The energy-level mismatch between the CsPbI₂Br perovskite and carbon electrodes, however, results in major energy loss and reduced power conversion efficiency (PCE) of C-PSCs. Herein, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) is used to manage the energy level, reduce defect densities, and improve the interface quality between CsPbI₂Br and carbon electrodes. Preliminary results demonstrate that the BMIMBF₄ modifier can passivate the surface defects of the perovskite film and reduce the energy-level mismatch between the CsPbI₂Br layer and the carbon electrode. A PCE of 14.03% is achieved by introducing BMIMBF₄ which is improved by 23% compared with the control device (11.37%). Moreover, stability—whether in the case of C-PSCs or CsPbI₂Br films—is also improved.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Thavamani Gokulnath, Jungmin Choi, Ho-Yeol Park, Kyungmin Sung, Yeongju Do, Hyungjin Park, Junyoung Kim, Saripally Sudhaker Reddy, Jehan Kim, Myungkwan Song, Jinhwan Yoon, Sung-Ho Jin

Publication date: 18 August 2021

Source: Joule, Volume 5, Issue 8

Author(s): Yunpeng Qin, Nrup Balar, Zhengxing Peng, Abay Gadisa, Indunil Angunawela, Anirban Bagui, Somayeh Kashani, Jianhui Hou, Harald Ade

Examination of single-crystal X-ray diffraction images between ≈500 and ≈100 K yields new symmetry assignments for CsPbBr₃. The space groups are: Im-3 above ≈410 K, P2₁/m between ≈410 K and ≈300 K, and Pm below ≈300 K. A unit cell volume of ≈2a_p × 2a_p × 2a_p is maintained. Local structural measurements reveal non-centrosymmetric short-range order above 300 K.

Abstract

Perovskite photovoltaic ABX₃ systems are being studied due to their high energy-conversion efficiencies with current emphasis placed on pure inorganic systems. In this work, synchrotron single-crystal diffraction measurements combined with second harmonic generation measurements reveal the absence of inversion symmetry below room temperature in CsPbBr₃. Local structural analysis by pair distribution function and X-ray absorption fine structure methods are performed to ascertain the local ordering, atomic pair correlations, and phase evolution in a broad range of temperatures. The currently accepted space group assignments for CsPbBr₃ are found to be incorrect in a manner that profoundly impacts physical properties. New assignments are obtained for the bulk structure: Im3¯ (above ≈410 K), P2₁/m (between ≈300 K and ≈410 K), and the polar group Pm (below ≈300 K), respectively. The newly observed structural distortions exist in the bulk structure consistent with the expectation of previous photoluminescence and Raman measurements. High-pressure measurements reveal multiple low-pressure phases, one of which exists as a metastable phase at ambient pressure. This work should help guide research in the perovskite photovoltaic community to better control the structure under operational conditions and further improve transport and optical properties.

A highly transparent, efficient, and stable 2D (〈n〉 = 2, according to the precursor stoichiometry) perovskite semitransparent photovoltaic (ST-PV) is demonstrated for application in building-integrated photovoltaics. By fully expanding the phase distribution and enhancing the out-of-plane orientation, the first average 〈n〉 = 2 2D ST-PV is realized with an average visible transmittance over 40% and power conversion efficiency of 7.52%.

Abstract

The application of low average layer-number (〈n〉 ≤ 2) 2D perovskites in semitransparent photovoltaics (ST-PVs) has been hindered by their strong exciton binding energy and high electrical anisotropy. Here, the phase distribution is expanded fully and orderly to enable efficient charge transport in 2D (NMA)₂(MA)Pb₂I₇ (NMA: 1-naphthylmethylammonium, MA: CH₃NH₃ ⁺) perovskite films by regulating the sedimentation dynamics of organic cation-based colloids. Ammonium chloride is synergistically introduced to enhance the phase separation further and construct a favorable out-of-plane orientation. The wide and graded phase distribution well aligns the energy level to facilitate charge transfer. As a result, the first application of an average 〈n〉 = 2 2D perovskite is implemented in ST-PVs with visible power conversion efficiency (PCE) of 7.52% and high average visible transmittance (AVT) of 40.5%. This study offers a new candidate and an effective strategy for efficient and stable ST-PVs and is relevant to other perovskite optoelectronic devices.

Highly efficient organic solar cells are fabricated using a ternary approach, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both donor and acceptor materials, and optimizes the ternary blend morphology. A record-high efficiency of 18.66% is consequently achieved.

Abstract

The ternary strategy, introducing a third component into a binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The judicious selection of an appropriate third component, without sacrificing the photocurrent and voltage output of the OSC, is of significant importance in ternary devices. Herein, highly efficient OSCs fabricated using a ternary approach are demonstrated, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. The three components show complementary absorption spectra and cascade energy alignment. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both the donor and acceptor materials, and optimizes the ternary blend morphology. Moreover, the addition of L8-BO-F into the binary blend suppresses the non-radiative recombination, thus leading to a reduced voltage loss. Consequently, concurrent increases in open-circuit voltage, short-circuit current, and fill factor are realized, resulting in an unprecedented PCE of 18.66% (certified value of 18.2%), which represents the highest efficiency values reported for both single-junction and tandem OSCs so far.

The catastrophic failure of n-i-p type perovskite solar cells under operation is reported, which is proven by the corrosion of the metal electrode on the edge. After inserting a thin MoO₃, the improved Ag thin film morphology as well as better energy alignment suppress the catastrophic failure of perovskite solar cells.

Abstract

The n-i-p type perovskite solar cells suffer unpredictable catastrophic failure under operation, which is a barrier for their commercialization. The fluorescence enhancement at Ag electrode edge and performance recovery after cutting the Ag electrode edge off prove that the shunting position is mainly located at the edge of device. Surface morphology and elemental analyses prove the corrosion of the Ag electrode and the diffusion of Ag⁺ ions on the edge for aged cells. Moreover, much condensed and larger Ag clusters are formed on the MoO₃ layer. Such a contrast is also observed while comparing the central and the edge of the Ag/Spiro-OMeTAD film. Hence, the catastrophic failure mechanism can be concluded as photon-induced decomposition of the perovskite film and release reactive iodide species, which diffuse and react with the loose Ag clusters on the edge of the cell. The corrosion of the Ag electrode and the migration of Ag⁺ ions into Spiro-OMeTAD and perovskite films lead to the forming of conducting filament that shunts the cell. The more condensed Ag cluster on the MoO₃ surface as well as the blocking of holes within the Spiro-OMeTAD/MoO₃ interface successfully prevent the oxidation of Ag electrode and suppress the catastrophic failure.

Stabilizing high-efficiency perovskite solar cells (PSCs) at operating conditions remains an unresolved issue hampering its large-scale commercial deployment. Here, we report a star-shaped polymer to improve charge transport and inhibit ion migration at the perovskite interface. The incorporation of multiple chemical anchor sites in the star-shaped polymer branches strongly controls the crystallization of perovskite film with lower trap density and higher carrier mobility and thus inhibits the nonradiative recombination and reduces the charge-transport loss. Consequently, the modified inverted PSCs show an optimal power conversion efficiency of 22.1% and a very high fill factor (FF) of 0.862, corresponding to 95.4% of the Shockley-Queisser limited FF (0.904) of PSCs with a 1.59-eV bandgap. The modified devices exhibit excellent long-term operational and thermal stability at the maximum power point for 1000 hours at 45°C under continuous one-sun illumination without any significant loss of efficiency.

Fluoride chemistry in tin halide perovskites improves the crystallization process. Fluoride anions selectively coordinate and remove Sn^IV and affect the colloidal properties in solution. This study describes the working mechanism of SnF₂ and highlights the importance of solution chemistry for controlling crystallization and Sn^II oxidation in tin halide perovskites.

Abstract

Tin is the frontrunner for substituting toxic lead in perovskite solar cells. However, tin suffers the detrimental oxidation of Sn^II to Sn^IV. Most of reported strategies employ SnF₂ in the perovskite precursor solution to prevent Sn^IV formation. Nevertheless, the working mechanism of this additive remains debated. To further elucidate it, we investigate the fluoride chemistry in tin halide perovskites by complementary analytical tools. NMR analysis of the precursor solution discloses a strong preferential affinity of fluoride anions for Sn^IV over Sn^II, selectively complexing it as SnF₄. Hard X-ray photoelectron spectroscopy on films shows the lower tendency of SnF₄ than SnI₄ to get included in the perovskite structure, hence preventing the inclusion of Sn^IV in the film. Finally, small-angle X-ray scattering reveals the strong influence of fluoride on the colloidal chemistry of precursor dispersions, directly affecting perovskite crystallization.