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A highly crystalline and wide bandgap electron acceptor, IDTT-M, is used to fabricate high efficiency ternary solar cells with PM6 and another narrow bandgap electron acceptor, Y6. Benefiting from efficient Förster resonance energy transfer, a significantly improved power conversion efficiency of up to 16.63% is achieved with simultaneously enhanced device characteristics.

Abstract

Introducing a third component into organic bulk heterojunction solar cells has become an effective strategy to improve photovoltaic performance. Meanwhile, the rapid development of non-fullerene acceptors (NFAs) has pushed the power conversion efficiency (PCE) of organic solar cells (OSCs) to a higher standard. Herein, a series of fullerene-free ternary solar cells are fabricated based on a wide bandgap acceptor, IDTT-M, together with a wide bandgap donor polymer PM6 and a narrow bandgap NFA Y6. Insights from the morphological and electronic characterizations reveal that IDTT-M has been incorporated into Y6 domains without disrupting its molecular packing and sacrificing its electron mobility and work synergistically with Y6 to regulate the packing pattern of PM6, leading to enhanced hole mobility and suppressed recombination. IDTT-M further functions as an energy-level mediator that increases open-circuit voltage (V _OC) in ternary devices. In addition, efficient Förster resonance energy transfer (FRET) between IDTT-M and Y6 provides a non-radiative pathway for facilitating exciton dissociation and charge collection. As a result, the optimized ternary device features a significantly improved PCE up to 16.63% with simultaneously enhanced short-circuit current (J _SC), V _OC, and fill factor (FF).

A hydrophobic ammonium salt, 4-(trifluoromethyl) benzylamine, is introduced to form a quasi-2D hybrid perovskite by a one-step spin-coating method. Due to the relatively low surface energy of fluorinated molecules, an upper gradient low-dimensional structure is formed spontaneously from top to bottom, and more stable devices are obtained with a power conversion efficiency of 17.07%.

Abstract

Highly efficient and stable quasi-2D hybrid perovskite solar cells (PSCs) using hydrophobic 4-(trifluoromethyl) benzylamine (4TFBZA) as the spacer cation are successfully demonstrated. It is found that the incorporation of hydrophobic 4TFBZA into MAPbI₃ can effectively induce a spontaneous upper gradient 2D (SUG-2D) structure, passivate the trap states, and restrain the ion motion. Meanwhile, the strong hydrogen bonding of F···HN between 4TFBZA ions and methylamine ions can effectively suppress the decomposition of perovskite, which gives the device a better thermal stability. Besides, due to the SUG-2D structure with hydrophobic 4TFBZA, the device also exhibits a better moisture stability. The SUG-2D-structure-based device exhibits a power conversion efficiency of 17.07% with a high open-circuit voltage of 1.10 V and a notable fill factor of 71%. This work provides a new strategy for constructing efficient and stable quasi-2D PSCs, and it is an inspiration for the packaging strategy of perovskites.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Yi Long, Yeming Xian, Songyang Yuan, Kun Liu, Mingyuan Sun, Yang Guo, Naveed Ur Rahman, Jiandong Fan, Wenzhe Li

A combined approach of simulation and experiment unravels the origin of very high external quantum efficiencies (EQEs up to 98% in the literature), which are frequently reported for highly efficient perovskite solar cells. The high refractive index of the perovskite and the thickness of the underlying transparent electrode are identified to mainly govern light in-coupling into the active layer.

With the emergence of highly efficient perovskite solar cells in both single- and multijunction architectures, there is an abundance of reports of extremely high external quantum efficiencies (EQE) up to 98%. Typically, the spectral maximum of the EQE is found in the range between 400 and 500 nm, which is even more surprising, as the transmittance of typically used indium tin oxide (ITO)/glass substrates does not exceed 90% in this wavelength range. Herein, the root cause of the high EQE values by a combination of experimental data and optical simulations is analyzed and explained. It is shown that the high refractive index of the perovskite absorber is strongly increasing the transmittance of incident light into the active perovskite layer, while the spectral distribution and ultimately the spectral position of the peak in the transmittance spectrum are strongly affected by the thickness and optical properties of the underlying transparent electrode.

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.

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.

For the first time, high-temperature perovskite solar cells (PSCs) are fabricated, which achieve decent efficiency and retain 80% of the initial efficiency after heating at 200 °C for 45 h. Their photovoltaic behavior under temperatures from 25 °C to over 200 °C is well investigated. This work may expand the application of PSCs into space exploration.

Herein, high-temperature (over 200 °C) perovskite solar cells (PSCs) are fabricated and studied for the first time. Inorganic CsPbI₂Br perovskite is used as absorber and carbon nanotubes (CNTs) are directly used as the hole extraction electrode. Such device retains over 80% of its initial power conversion efficiency (PCE) after heating at 200 °C for 45 h, enabling its operation at high temperatures. By recording reverse and forward J–V curves at different temperatures (25–220 °C), temperature coefficients of photovoltaic parameters are obtained. Compared with conventional high-temperature solar cells (Si, CuInGaSe, and GaAs), CsPbI₂Br devices show superior V _OC and FF temperature coefficients but inferior J _SC temperature coefficients. As a result, PCE temperature coefficients of CsPbI₂Br devices are superior over Si and CuInGaSe solar cells, and are comparable with those of GaAs solar cells. Meanwhile, the mitigation of charge accumulation at elevated temperatures results in a gradual decrease in J–V hysteresis. Therefore, this study may expand the application of PSCs into high-temperature fields, such as space exploration.

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

Publication date: 15 September 2021

Source: Joule, Volume 5, Issue 9

Author(s): Quan Liu, Sander Smeets, Sigurd Mertens, Yuxin Xia, Andrea Valencia, Jan D’Haen, Wouter Maes, Koen Vandewal

Aiming at improving the performance of tin perovskite solar cells, this study analyzes the Sn²⁺ oxidation process in the precursor solution and proposes a source-regulating strategy to prepare high-quality perovskite films with low Sn⁴⁺ defect densities. A device with high certified efficiency and excellent long-term stability is obtained.

Abstract

Tin-based halide perovskites have attracted great attention in the perovskite solar cells (PSCs) community with their suitable band gaps, excellent optoelectronic properties, and non-toxicity. However, because of their poor chemical stability, it is challenging to fabricate highly stable and efficient tin PSCs (TPSCs). In this study, the origin of the Sn²⁺ oxidation ahead of film formation is concentrated on, and it is found that the ionization of SnI₂ in precursor plays a decisive role. Accordingly, SnI₂ dissociation and the subsequent Sn²⁺ oxidation can be restricted in precursor by employing reductive complexes as additives. This dual-functional source-regulating strategy effectively helps prepare high-quality perovskite films with low Sn⁴⁺ defect densities. As a result, the unencapsulated TPSCs show a considerable power-conversion efficiency of 10.03% (certified 9.38%) and maintain 90% of its initial efficiency after 1000 h of light aging testing.

An oxygen-rich activated carbon (AC) is synthesized from the abundant biomass material cellulose. The obtained AC exhibits a high specific area and possesses a high oxygen content, elevating carbon electrodes (CEs) work functions and promoting the contact between CEs and perovskites. As a result, printable mesoscopic perovskite solar cells's power conversion efficiency is enhanced from 13.8% to 15.5% using the CEs including AC.

Carbon electrodes (CEs) are demonstrated as the most stable and cost-effective back electrodes for perovskite solar cells (PSCs), which influence the performance of related PSCs significantly. Herein, oxygen-rich activated carbon (AC) is synthesized from the most abundant biomass resource, cellulose, via a feasible carbonization and oxidization process and applied in CEs for hole-conductor-free printable mesoscopic PSCs (p-MPSCs). The obtained cellulose-based activated carbon (CAC) exhibits a high specific area of 477.14 m² g⁻¹ and possesses a high oxygen content of 11.9%, promoting the wettability and contact between CEs and perovskites. Moreover, the high oxygen content also leads to an elevated work function of CEs. As a result, p-MPSCs filled with (5-AVA)_0.03(MA)_0.97PbI₃ based on CEs containing CAC give an efficiency of 15.5%, whereas those devices based on CEs with no CAC give an efficiency of 13.8%. The improved efficiency benefits from the promoted fill factor and open circuit voltage due to the optimized energy level alignment and enhanced charge extraction by CAC. This work presents a good example for the value-added utilization of cellulose in the energy conversion systems and offers a feasible strategy for preparing oxygen-rich CE for PSCs with enhanced performance.

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.

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 novel, rapid, and scalable treatment method that significantly improves perovskite thin film crystallinity is introduced. Treated perovskite solar cells (PSCs) exhibit enhanced efficiencies, increased stabilities, and improved reproducibility. Versatility and universality are demonstrated using: CH₃NH₃PbI₃ (MAPbI₃) PSCs with thicknesses from 500–1300 nm; large-area (>1 cm²) devices; a range of device architectures and compositions including Cs_0.1FA_0.9Pb(I_0.95Br_0.05) devices.

Abstract

Metal-halide perovskite solar cells (PSCs) have had a transformative impact on the renewable energy landscape since they were first demonstrated just over a decade ago. Outstanding improvements in performance have been demonstrated through structural, compositional, and morphological control of devices, with commercialization now being a reality. Here the authors present an aerosol assisted solvent treatment as a universal method to obtain performance and stability enhancements in PSCs, demonstrating their methodology as a convenient, scalable, and reproducible post-deposition treatment for PSCs. Their results identify improvements in crystallinity and grain size, accompanied by a narrowing in grain size distribution as the underlying physical changes that drive reductions of electronic and ionic defects. These changes lead to prolonged charge-carrier lifetimes and ultimately increased device efficiencies. The versatility of the process is demonstrated for PSCs with thick (>1 µm) active layers, large-areas (>1 cm²) and a variety of device architectures and active layer compositions. This simple post-deposition process is widely transferable across the field of perovskites, thereby improving the future design principles of these materials to develop large-area, stable, and efficient PSCs.

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.

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.