Chen Weijie

Fabricating high-quality perovskite film in the ambient air is significantly important for upcoming commercial production. Here, the perovskite crystallization process by a two-step sequential solution deposition in a glovebox and air is systematically studied. Thermal-radiation-assisted ultrafast conversion from the intermediates to perovskite is demonstrated, and a comparable performance for the device from the glovebox is acheived.

Abstract

Fabricating perovskite solar cells (PSCs) in air is conducive to low-cost commercial production; nevertheless, it is rather difficult to achieve comparable device performance as that in an inert atmosphere because of the poor moisture toleration of perovskite materials. Here, the perovskite crystallization process is systematically studied using two-step sequential solution deposition in an inert atmosphere (glovebox) and air. It is found that moisture can stabilize solvation intermediates and prevent their conversion into perovskite crystals. To address this issue, thermal radiation is used to accelerate perovskite crystallization for integrated perovskite films within 10 s in air. The as-formed perovskite films are compact, highly oriented with giant grain size, superior photoelectric properties, and low trap density. When the films are applied to PSC devices, a champion power conversion efficiency (PCE) of 20.8% is obtained, one of the best results for air-processed inverted PSCs under high relative humidity (60 ± 10%). This work substantially assists understanding and modulation to perovskite crystallization kinetics under heavy humidity. Also, the ultrafast conversion strategy by thermal radiation provides unprecedented opportunities to manufacture high-quality perovskite films for low-temperature, eco-friendly, and air-processed efficient inverted PSCs.

The isogenous acceptor strategy improves the power conversion efficiency (PCE) of organic solar cells (OSCs) from 17.37% to 18.03% by maximizing light absorption and optimizing the morphology of the active layer.

Isogenous acceptor strategy is considered to be able to effectively improve the power conversion efficiency (PCE) of ternary organic solar cells (OSCs) by maximizing the absorption and optimizing the morphologies of active layers. Herein, a Y6-like small-molecular non-fullerene acceptor of m-BTP-PhC6 is employed as the second acceptor to tune the photovoltaic performance of D18-Cl:Y6:m-BTP-PhC6-based ternary OSCs. A highest PCE up to 18.03% is achieved with an optimized Y6:m-BTP-PhC6 blend ratio of 4:1, with a V _OC of 0.871 V, a J _SC of 26.80 mA cm⁻², and a FF of 77.32%, respectively. Compared to D18-Cl:Y6 binary system, it was found that the introduction of m-BTP-PhC6 expanded the spectral absorption range and provided a good cascade energy level matching. The light intensity dependence results demonstrate that ternary blending could significantly promote the photogenerated charge dissociation and transporting, meanwhile suppressing the bimolecular recombination. Transient absorption (TA) results further depicted a decay lifetime of 0.84 ps of D18-Cl:Y6 binary in contrast to 0.69 ps of the D18-Cl:Y6:m-BTP-PhC6 ternary film, indicating a faster hole transfer dynamic. The work presents a promising isogenous acceptor strategy to improve the efficiency of ternary OSCs.

An ultra-wide bandgap polymer donor (≈2.87 eV) is developed for efficient wavelength-selective transparent polymer solar cells. The solution-processed polymer solar cells obtain a power conversion efficiency of >3% along with outstanding average visible transmittance of >50%.

Wavelength-selective transparent polymer solar cells (T-PSCs) have huge developing potential in power-window applications for their excellent visible transparency and high color-rendering index. However, the main research interest of devices until now is focused on near-infrared absorbers for both polymer donor and nonfullerene small-molecule acceptor (NF-SMA) due to the lack of appropriate near-ultraviolet absorbers. Herein, the successful implementation of the T-PSC devices based on novel kinds of near-ultraviolet polymer donors combined with a near-infrared NF-SMA Y6 is reported. The reported polymer donors are “D1–D2”-type copolymers employing fluorene and triphenylamine as the two electron-donating units. The best-performed one not only shows ultrawide optical bandgap (2.87 eV), leading to high average visible transmittance (AVT) of 96.8% in the thin film, but also has efficient hole mobility (about 5.0 × 10⁻⁶ cm² V⁻¹ s⁻¹), well-matched frontier molecular orbital energy levels, and good miscibility with Y6. As a result, the T-PSC device is obtained with an AVT of 51.4% and PCE of 3.15%, along with favorable light utilization efficiency (LUE) of 1.62% and CRI of 91.6. This is the first example that uses near-ultraviolet-absorbed polymer donor to achieve high-efficiency T-PSC devices.

UV irradiation is applied on the perovskite film during their thermal annealing process. The crystallization is greatly improved and the perovskite film is very smooth. As a result, both the power conversion efficiency (PCE) and stability of the resulted solar cells are considerably enhanced. A PCE of 23.24% is achieved.

Highly crystalized perovskite film with smooth surface is of great importance to obtain high photovoltaic performances. Herein, UV irradiation is applied to the perovskite films during their thermal annealing process. It is revealed that UV irradiation treatment can largely improve perovskite crystallization and reduce defects. This greatly improves power conversion efficiency (PCE) and environmental stability of the resulted solar cells (ITO/SnO₂/perovskite/Spiro-OMeTAD/Au). By combining CH₃O-PEAI surface passivation, an outstanding PCE of 23.24% is achieved.

Research progress on the development of efficient and stable FAPbI₃ perovskite solar cells is reviewed with a focus on the strategies for stabilizing the phase of α-FAPbI₃. In detail, solvent engineering, composition engineering, additive engineering, as well as other approaches are discussed systematically. Finally, the challenges and development prospects for future study are proposed.

With the advantages of narrow bandgap and excellent thermal stability, fomamidinium lead triiodide (FAPbI₃) perovskite holds the promise to boost the power conversion efficiency (PCE) of perovskite solar cells (PSCs) to over 25%. However, such a promise is blurred by the poor structural stability of the black α-phase FAPbI₃, as it can spontaneously transform into photoinactive δ-phase at room temperature and this process can be accelerated by the ambient moisture. The incorporation of small ions such as cesium (Cs⁺), methylammonium (MA), and bromide (Br⁻) into the perovskite lattice is proven to be successful in stabilizing the α-phase FAPbI₃; however, the resultant mixed perovskites suffer the phase segregation problem, which inevitably undermines the long-term stability of the corresponding PSCs. Therefore, continuous efforts are made to realize stable and pure-phase α-FAPbI₃ perovskites. Herein, the recent progress on the development of efficient and stable FAPbI₃ PSCs is summarized with a focus on the different phase stabilization strategies. In addition, the challenges and possible directions for future study are proposed.

A facile method is reported to improve the interface contact between SnO₂ and perovskite by introduced a multifunctional interfacial crosslinking agent D-penicillamine (DPM). The efficiency of DPM-modified device is increased from 22.44% to 24.09%. Meanwhile, an unencapsulated DPM-modified device exhibited better stability and in-situ absorption capacity of leaked lead ions than the controlled device.

SnO₂-based planar perovskite solar cells (PSCs) have attracted extensive attention owing to their simple structure and low-temperature processing. However, the imperfect interface contact caused by surface defects and energy-level mismatches greatly hinder the further improvement of the efficiency and stability of PSC. Herein, a multifunctional interfacial crosslinking agent D-penicillamine (DPM) is introduced to improve the interface contact between SnO₂ and upper perovskite. Through systematical analysis, it is found that the DPM used to modify SnO₂ can simultaneously passivate the defects on the surface of SnO₂ via esterification reaction, promote the charge extraction in perovskite by adjusting the interface energy-level arrangement, and improve the quality of perovskite film by forming coordination bond with lead ions. These merits eventually assist DPM-modified PSCs and achieve an impressive efficiency of 24.09%, whereas the controlled device only shows an efficiency of 22.44%. In addition, an unencapsulated DPM-modified PSC exhibits better storage stability, thermal stability, and light stability than the controlled device, as well as in situ absorption capacity of leaked lead ions.

High open-circuit voltage semitransparent solar cells are obtained employing phase stable wide bandgap perovskite absorbers. Mechanically stacked, four-terminal perovskite/silicon tandem solar cells with over 30% efficiency are successfully fabricated using a highly efficient semitransparent perovskite solar cell as the front-cell and a silicon heterojunction solar cell as the back-cell.

Abstract

Wide-bandgap perovskite solar cells (PSCs) with an optimal bandgap between 1.7 and 1.8 eV are critical to realize highly efficient and cost-competitive silicon tandem solar cells (TSCs). However, such wide-bandgap PSCs easily suffer from phase segregation, leading to performance degradation under operation. Here, it is evident that ammonium diethyldithiocarbamate (ADDC) can reduce the detrimental I₂ back to I⁻ in precursor solution, thereby reducing the density of deep level traps in perovskite films. The resultant perovskite film exhibits great phase stability under continuous illumination and 30–60% relative humidity conditions. Due to the suppression of defect proliferation and ion migration, the PSCs deliver great operation stability which retain over 90% of the initial power conversion efficiency (PCE) after 500 h maximum power point tracking. Finally, a highly efficient semitransparent PSC with a tailored bandgap of 1.77 eV, achieving a PCE approaching 18.6% with a groundbreaking open-circuit voltage (V _OC) of 1.24 V enabled by ADDC additive in perovskite films is demonstrated. Integrated with a bottom silicon solar cell, a four-terminal (4T) TSC with a PCE of 30.24% is achieved, which is one of the highest efficiencies in 4T perovskite/silicon TSCs.

A flexible perovskite solar cell for indoor applications is fabricated. A record efficiency of 31% and 25%, and 23% at 1000 lux (393.6 W cm⁻²) is obtained for a device with an electrode of metal, carbon and carbon with no hole extraction layer, respectively. Carbon devices lost only 20% of its initial efficiency after 1000 h under Maximum Power Point Tracking.

Abstract

Perovskite Solar Cells (PSCs) are well known for their high efficiencies under 1 sun (AM1.5G), however, PSC can also generate power by harvesting the low-light available indoors. Here, three flexible PSC architectures are presented for indoor applications: with a metal electrode aiming for high efficiency; carbon electrode aiming for high stability and compatibility with large-scale production; and hole transport material (HTM)-free carbon for simplifying the fabrication process. A maximum efficiency of 30.9% (30.0%) under 1000 lux (200 lux) is obtained for a PSC with gold electrode. A maximum efficiency of 25.4% (24.7%) and 23.1% (22.3%) is obtained for the carbon devices with and without HTM, respectively, under 1000 lux (200 lux). To the best of the author's knowledge, the efficiency values presented here for a device with a carbon-based electrode, with and without HTM, are the record values for a flexible PSC at indoor light conditions. Furthermore, the HTM-free carbon device kept 84% of its initial efficiency after 1000 h at MPPT and lost virtually no performance after 1000 h at 85 °C. Also, non-encapsulated devices of all configurations withstood 1600 h in air with a maximum loss in efficiency of 6%.

The Cs₄PbI₆-antisolvent adduct reduces the transformation energy barrier and induces the accelerated crystallization of dimethylammonium-iodide-assisted CsPbI₃, thereby highlighting the predominant role of the Cs₄PbI₆ intermediate. Rapid crystallization of anisole antisolvent bathing allows smooth and uniform coverage of the film with fewer defects and pinholes, thereby enhancing the power conversion efficiency of the CsPbI₃ solar cells to 18.84%, under ambient condition.

Abstract

Antisolvent treatment has been developed to effectively fabricate dimethylammonium-iodide (DMAI)-assisted CsPbI₃ perovskite solar cells (PSC) under moisture conditions. However, a clear understanding of its effect on the crystallization mechanism is still elusive. Here, the antisolvent bathing effect on DMAI-assisted CsPbI₃ crystallization is investigated under ambient conditions. For films bathed into antisolvents with Lewis basic oxygen (i.e., diethyl ether, anisole, ethyl acetate, and methyl acetate), rapid crystallization kinetics are observed due to the interaction between Cs₄PbI₆ and antisolvent in the form of the adduct. The Cs₄PbI₆-antisolvent adduct lowers the transformation energy barrier, thereby enabling immediate phase transformation to CsPbI₃ as soon as DMAPbI₃ is decomposed. Based on this observation, a new crystallization mechanism is proposed for DMAI-assisted CsPbI₃ in which Cs₄PbI₆, instead of DMAPbI₃, plays the role of the predominant phase of crystallization. Accelerated crystallization due to anisole antisolvent bathing results in a uniform film morphology and better coverage with fewer defects and pinholes. This enhances the power conversion efficiency of the n-i-p-structured PSCs based on anisole-bathed CsPbI₃ to 18.84%, even under moisture conditions.

An n-type semiconductor (B4PyPPM) modifies a perovskite film via an anti-solvent method. B4PyPPM can inhibit nonradiative recombination in the perovskite bulk, increase the built-in potential, improve the Fermi level of the modified perovskite film, and facilitate the extraction of electrons to the electron transport layer. The champion sample achieves a high efficiency of 23.51% and excellent operational stability.

Abstract

Because of the compatibility with tandem devices and the ability to be manufactured at low temperatures, inverted perovskite solar cells have generated far-ranging interest for potential commercial applications. However, their efficiency remains inadequate owing to various traps in the perovskite film and the restricted hole blocking ability of the electron transport layer. Thus, in this work, a wide-bandgap n-type semiconductor, 4,6-bis(3,5-di(pyridin-4-yl)phenyl)-2-phenylpyrimidine (B4PyPPM), to modify a perovskite film via an anti-solvent method is introduced. The nitrogen sites of pyrimidine and pyridine rings in B4PyPPM exhibit strong interactions with the undercoordinated lead ions in the perovskite material. These interactions can reduce the trap state densities and inhibit nonradiative recombination of the perovskite bulk. Moreover, B4PyPPM can partially aggregate on the perovskite surface, leading to an improvement in the hole-blocking ability at its interface. This modification can also increase the built-in potential and upshift the Fermi level of the modified perovskite film, promoting electron extraction to the electron transport layer. The champion device achieves a high efficiency of 23.51%. Meantime, the sealed device retains ≈80% of its initial performance under a maximum power point tracking for nearly 2400 h, demonstrating an excellent operational stability.

A stable supramolecular organization modulating strategy is developed to modulate unreacted PbI₂ and address both the efficiency and stability issues of perovskite solar cells. The self-assembled supramolecule is demonstrated to be extremely stable under continuous light illumination in the ambient environment, thus efficiently eliminating the detrimental stability effect of unreacted PbI₂.

Abstract

Excess PbI₂ in perovskite film is an effective strategy for boosting perovskite solar cells (PSCs) performance. However, the presence of unreacted PbI₂ is a critical source of intrinsic instability in perovskite under illumination, due to the photolysis of PbI₂ (decomposed into metallic lead and iodine). Herein, this issue is solved by applying ionic liquids (ILs) on PSCs where the ILs can form types of stable supramolecules with residual lead iodide. The formation process and mechanism of the supramolecules are elucidated. The residual PbI₂ is also revealed to cause high level lead interstitial defects and induced tensile strain which further deteriorate device performance. The self-assembled supramolecular complex can passivate the PSCs where significant enhancements are achieved in both power conversion efficiency (PCE, from 21.9% to 23.4%) and device stability (retaining 95% of the initial PCE after 4080 h in ambient dry-air storage, and 80% after 1400 h continuous light illumination).

An innovative interface modification method developed for the three interfaces of a lead sulfide colloidal quantum dot solar cell allows precise control of the photogenerated carriers across the device, balancing carrier extraction while minimizing nonradiative recombination at each interface of the device, increasing carrier extraction efficiency at the maximum power point and power conversion efficiency by over 15%.

Abstract

Lead sulfide colloidal quantum dot solar cells (CQDSCs), the next generation of photovoltaics, are hampered by non-radiative recombination induced by defects and an electron-hole extraction imbalance. CQDSCs have three interfaces: CQD/CQD, electron transport layer (ETL)/CQD, and CQD/hole transport layer (HTL), and modifying one of these interfaces does not fix the problem stated above. Here, coordinated control and passivation of the three interfaces in PbS CQDSCs are presented and it is shown that the synergistic effects may improve charge transport and charge carrier extraction balance and minimize non-radiative recombination simultaneously. A facile method is developed for epitaxially growing an ultrathin perovskite shell on the CQD surface to passivate the CQD/CQD interface, resulting in CQD absorber layers with long carrier diffusion lengths. With the introduction of organic films with adjustable electrical characteristics, the influence of ETL/CQD interfacial modifications on carrier transport and recombination is investigated. An excessive increase in the electron extraction rate reduces the fill factor and solar efficiency, as discovered. Therefore a modified layer is created at the CQD/HTL interface to promote hole extraction, which enhances charge extraction balance and passivates the interface. Finally, PbS CQDSCs exhibit a power conversion efficiency of 15.45%, a record for Pb chalcogenide CQDSCs.

An intrinsically lead-poor surface is found on CsPbI₃ films and it limits the efficiency improvement of inverted CsPbI₃ perovskite solar cells for inferior electron transfer and serious nonradiative recombination at CsPbI₃/6,6-phenyl C61-butyric acid methyl ester interface. Compared to molecular passivation, 1,4-butanediamine can polish the lead-poor surface for fluent electron transfer, and significantly improve the V _oc and fill factor with a recorded efficiency of 19.84% and excellent stability.

Abstract

Triiodide cesium lead perovskite (CsPbI₃) has promising prospects in the development of efficient and stable photovoltaics in both single-junction and tandem structures. However, achieving inverted devices that provide good stability and are compatible to tandem devices remains a challenge, and the deep insights are still not understood. This study finds that the surface components of CsPbI₃ are intrinsically lead-poor and the relevant traps are of p-type with localized states. These deep-energy-level p traps induce inferior transfer or electrons and serious nonradiative recombination at the CsPbI₃/PCBM interface, leading to the considerable open-circuit voltage (V _oc) loss and reduction of fill factor (FF). Compared to molecular passivation, polishing treatment with 1,4-butanediamine can eliminate the nonstoichiometric components and root these intrinsically lead-poor traps for superior electron transfer. The polishing treatment significantly improves the FF and V _oc of the inverted CsPbI₃ photovoltaics, creating an efficiency promotion from 12.64% to 19.84%. Moreover, 95% of the initial efficiency of the optimized devices is maintained after the output operation for 1000 h.

A perovskite quantum dot (PQD) solid with a high orientation and substantially diminished nonradiative recombination is constructed using precursor engineering accompanied by a chemical stripping treatment of the PQDs. Consequently, the resultant inorganic PQD solar cell (PQDSC) delivers a high power conversion efficiency of up to 16.25%, among the highest efficiencies of inorganic PQDSCs.

Abstract

Perovskite quantum dots (PQDs) have emerged as competitive optoelectronic materials for photovoltaic applications due to their ideal bandgap energy, high defect tolerance, and solution processability. However, the highly dynamic surface and imperfect cubic structure of PQDs generally result in unfavorable charge-carrier transport within the PQD solids and serious nonradiative recombination. Herein, a highly orientated PQD solid is demonstrated using precursor engineering accompanied by a chemical stripping treatment (CST). A combination of systematic experimental studies and theoretical calculations is conducted to fundamentally understand the resurfacing of PQDs using the CST approach. The results reveal that the highly ordered PQDs can result in a high orientation of PQD solids, significantly promoting charge-carrier transport within the PQD solids. Meanwhile, the ideal cubic-structured PQD with an iodine-rich surface dramatically decreases surface trap states, thereby substantially diminishing trap-assisted nonradiative recombination. Consequently, the inorganic PQD solar cell delivers a power conversion efficiency of up to 16.25%. This work provides a feasible avenue to construct highly orientated PQD solids with improved photophysical properties for high-performance optoelectronic devices.

A robust transfer-printing method is developed using an ultrathin chemical bonding interfacial layer. The transfer-printed perovskite light-emitting diodes (LEDs) exhibit similar performance as optimized spin-coated LEDs, and the transfer-printed nanostructure reaches a high resolution up to 1270 ppi. A white perovskite LED structure is finally demonstrated with laterally aligned red and sky-blue perovskite microstripes made by the multiple transfer-printing process.

Abstract

Most methods of depositing perovskite films cannot meet the diverse requirements of real applications such as depositing films on various types of substrates, making patterns with different bandgaps for full-color display. Here, a robust mass transfer method of perovskite films and nanostructures is reported, meeting those requirements, by using an ultrathin branched polyethylenimine as interfacial chemical bonding layers. The transfer-printed perovskite films exhibit comparable morphology, composition, optoelectronic properties, and device performances with the counterparts made by optimized spin-coating methods. The perovskite light-emitting diodes (PeLEDs) using the transfer-printed films show decent external quantum efficiencies of 10.5% and 6.7% for red (680 nm) and sky-blue (493 nm) emissions, which are similar to the devices made by spin-coating. This robust transfer printing method also enables the the preparation of perovskite micropatterns with a high resolution up to 1270 pixels per inch. Horizontally aligned red and sky-blue perovskite microstripes are further obtained through multiple printing processes for white PeLEDs. This work demonstrates a feasible strategy for making perovskite films or micropatterns on various substrates for real applications in full-color display, white LEDs, lasing, etc.

A series of CH molecules with a new modification site on the central unit of Y-series electron acceptors has been designed and synthesized to afford better-performing organic solar cells (OSCs). Further fluorination on the largely unexplored central unit enabled significantly improved photovoltaic performance with over 18% efficiency for CH6-based binary OSCs.

Abstract

Halogenation of terminal of acceptors has been shown to give dramatic improvements in power conversion efficiencies (PCEs) of organic solar cells (OSCs). Similar significant results could be expected from the halogenation of the central units of state-of-the-art Y-series acceptors. Herein, a pair of acceptors, termed CH6 and CH4, featuring a conjugation-extended phenazine central unit with and without fluorination, have been synthesized. The fluorinated CH6 has enhanced molecular interactions and crystallinity, superior fibrillar network morphology and improved charge generation and transport in blend films, thus affording a higher PCE of 18.33 % for CH6-based binary OSCs compared to 16.49 % for the non-fluorinated CH4. The new central site offers further opportunities for structural optimization of Y-series molecules to afford better-performed OSCs and reveals the effectiveness of fluorination on central units.

Publication date: 1 October 2022

Source: Electrochimica Acta, Volume 428

Author(s): Xiaoxu Sun, Haipeng Jiang, Yansen Sun, Zonghan Guo, Zhenyu Pang, Fengyou Wang, Jinghai Yang, Lili Yang