Chen Weijie

Publication date: January 2022

Source: Nano Energy, Volume 91

Author(s): Yun Meng, Xin Li, Shancheng Wang, ChooiKim Lau, Hebing Hu, Yujie Ke, Gang Tan, Junyou Yang, Yi Long

Publication date: January 2022

Source: Nano Energy, Volume 91

Author(s): Zhenhua Xu, Linxiang Zeng, Jinlong Hu, Zhen Wang, Putao Zhang, Christoph J. Brabec, Karen Forberich, Yaohua Mai, Fei Guo

Publication date: January 2022

Source: Nano Energy, Volume 91

Author(s): Wenhui Li, Xiaoyu Gu, Chengwei Shan, Xue Lai, Xiao Wei Sun, Aung Ko Ko Kyaw

Herein, it is demonstrated that the regulatory requirement to limit exposure of solvent vapors generated from ink-based coating process can be economically limiting for perovskite photovoltaics. A technoeconomic framework and solubility model was developed to guide ink development which leads to the development of an ink system with a 12× higher exposure limit than what is commonly used in the field.

Printed lead-based perovskite photovoltaics (PV) have gained interest due to their potential to be manufactured with scalable roll-to-roll techniques. In industrial scale-up, toxicity of inks can constrain roll-to-roll manufacturing due to the added cost of managing toxic effluents. Due to solvent toxicity, few perovskite solution chemistries in published works are scalable to gigawatt production capacity at low cost. Herein, it is shown that for scalable PV production, the use of aprotic polar solvents should be avoided due to their overall toxicity. Compliance with worldwide worker safety regulations for solvent exposure limits could require additional air handling requirements for some solvents, which in turn would affect cost-effectiveness. It is shown that costs associated with handling of hazardous substances can be significant and estimate an added cost of ¢3.7/W for dimethylformamide (DMF)-based inks. To solve this problem, a new perovskite ink solvent system is developed that is composed entirely of ether and alcohol, which has an effective exposure limit 14× higher than DMF, making it suitable for industrial coating processes. It is shown that the new ink solvent system is capable of fabricating high-efficiency perovskite solar cells processed in 1 min on a standard roll-to-roll system.

Pb source plays a critical role in determining the solution-processed perovskite film's crystallization, structural, and optoelectronic properties. This review comprehensively summarized the current understanding and advanced development of Pb source engineering in perovskite solar cells (PSCs), which is hoped to motivate more ideas toward further development of high-performing PSCs with controllable, sustainable, and large-scale production.

Organic–inorganic hybrid Pb halide perovskites have gained much attention as the most promising next generation photovoltaics, and the certificated power conversion efficiency of perovskite solar cells (PSCs) has recently reached 25.5%. For the typical solution-processed film, the features of solutes in the precursor solution greatly influence the characteristics of the deposited film. While for Pb-based perovskites, PbI₆ octahedral is the key component of the perovskite framework, and thus the Pb source particularly plays a significant role in determining the crystallization, structural, and optoelectronic properties of the solution-processed perovskite film. In this review, the state-of-the-art studies that focus on disclosing the key role of Pb source in the performance improvement of PSCs are systematically summarized. In addition, a comprehensive discussion on the effect of various Pb sources (e.g., Pb halides, Pb salts, Pb chalcogens, metallic Pb, and recycled Pb compounds) on the crystallization kinetics and photovoltaic characteristics of perovskite film is given. Also, the significant role of Pb source in producing large-scale PSCs in a controllable and sustainable manner is highlighted. This review is expected not only to put steps forward for the future commercialization of PSCs, but also to inspire more ideas in many other optoelectronic devices regarding raw material engineering.

Herein, surface modifications based on physical (UV−ozone, oxygen, argon, and/or helium plasma), chemical (interlayer passivation), and doping treatments and their impacts on the structural and optoelectronic properties of NiO _x are discussed. The effects of modified NiO _x films in p−i−n perovskite solar cells’ (PSCs’) power conversion efficiency (PCE) are also examined together with the current challenges and future outlooks.

The performances of perovskite solar cells (PSCs) largely depend on the perovskite compositions and the selection of electron and hole transport layers (ETLs and HTLs). The p-type NiO _x films are largely used as HTLs in p-i-n PSCs, thanks to their high transparency, processing versatility, cost-effectiveness, and easy integration within tandem devices. Several studies have shown that surface modifications on NiO _x films remove the surface defects, increase the NiO _x conductivity, and alter the band offset, consequently improving the interfaces between NiO _x films and the perovskite active layer. Indeed, besides improving the NiO _x intrinsic properties, the surface treatments also lead, in many cases, to superior perovskite quality driving high photovoltaic performance.

Alkyl-chain branching of non-fullerene acceptors flanking conjugated side-groups enables optimized optoelectronic and morphological properties, affording device performance of over 18%.

Abstract

Side-chain modifications of non-fullerene acceptors (NFAs) are essential for harvesting their full potential in organic solar cells (OSC). Here, an effective alkyl-chain-branching approach of the Y-series NFAs flanking meta-substituted phenyl side groups at the outer positions is demonstrated. Compared to BTP-4F-PC6 with linear m-hexylphenyl chains, two new acceptors named BTP-4F-P2EH and BTP-4F-P3EH are developed with bulkier alkyl chains branched at the β and γ positions, respectively. These branched chains result in altered molecular packing of the NFAs and afford higher open-circuit voltage of the devices. Despite the blue-shifted absorption of the branched-chain NFAs, their blends with PBDB-T-2F enable improved short-circuit current density for the corresponding devices owing to the more suitable phase separation and better exciton dissociation. Consequently, the OSCs based on BTP-4F-P2EH and BTP-4F-P3EH yield enhanced device performance of 18.22% and 17.57%, respectively, outperforming the BTP-4F-PC6-based ones (17.22%). These results highlight that the side-chain branching design of NFAs has great potential in optimizing molecular properties and promoting photovoltaic performance.

Homojunctions based on bipolar small π-conjugated molecules represent the ultimate stage of simplification of organic solar cells. Besides the fundamental questions posed by the possible direct photogeneration of charges–carriers and their transport, this concept can potentially contribute to the elimination of some of the major technical obstacles which limit the industrial scale development of organic photovoltaics.

Abstract

Single-material organic solar cells (SMOSCs) are on the forefront of research on organic photovoltaics (OPV). The generic term of SMOSCs encompasses a large variety of chemical structures implying very different basic concepts. Polydisperse «double cable» polymers and oligomers with acceptor groups linked to the conjugated backbone by a flexible spacer and donor–acceptor block copolymers are at present, the most investigated and efficient systems with spectacular progress in conversion efficiency achieved in the past 2–3 years. However, besides this mainstream SMOSCs research, a few recent publications describe OPV cells constituted of homojunctions based on small π-conjugated molecules. While the process of charge generation in such systems is still a matter of debate due in particular to the possible direct photogeneration of charge–carriers, devices with significant performance have been recently reported. After a brief overview of the most recent advances on the various types of SMOSCs, recent remarkable results on homojunction OPV cells based on small π-conjugated molecules are discussed in order to highlight the potential fundamental and technological interest of this emerging field of research.

Formamidinium (FA)-based additives in precursor solutions suppressed the formation of the undesired δ phase during the crystallization of FAPbI₃ perovskites, and heat-induced permeation of 4-tert-butylbenzylammonium iodide (tBBAI) into inner perovskite grains stabilized the α structure. Solar cells assembled from this material exhibited improved power conversion efficiency and stability.

Abstract

α-Formamidinium lead iodide (α-FAPbI₃) is one of the most promising candidate materials for high-efficiency and thermally stable perovskite solar cells (PSCs) owing to its outstanding optoelectrical properties and high thermal stability. However, achieving a stable form of α-FAPbI₃ where both the composition and the phase are pure is very challenging. Herein, we report on a combined strategy of precursor engineering and grain anchoring to successfully prepare methylammonium (MA)-free and phase-pure stable α-FAPbI₃ films. The incorporation of volatile FA-based additives in the precursor solutions completely suppresses the formation of non-perovskite δ-FAPbI₃ during film crystallization. Grains of the desired α-phase are anchored together and stabilized when 4-tert-butylbenzylammonium iodide is permeated into the α-FAPbI₃ film interior via grain boundaries. This cooperative scheme leads to a significantly increased efficiency close to 21 % for FAPbI₃ perovskite solar cells. Moreover, the stabilized PSCs exhibit improved thermal stability and maintained ≈90 % of their initial efficiency after storage at 50 °C for over 1600 hours.

Partial replacement (5–15%) of methylammonium (MA) in the MAPbI₃ perovskite by cesium or guanidinium (Gua) cations is demonstrated by X-ray diffraction, revealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation, respectively. The power conversion efficiency improves from an average value of 18.6% for the MAPbI₃ to a value of 20.0% for the Cs_0.05Gua_0.05MA_0.90PbI₃ perovskite.

The overall impact of the partial replacement (5–15%) of methylammonium (MA) in the MAPbI₃ perovskite by cesium or guanidinium (Gua) cations to fabricate thin films of triple cation Cs _x Gua _y MA_1–x–y PbI₃ perovskites is studied. The structural changes are investigated by using X-ray diffraction measurements revealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation, respectively. The optoelectronic properties are characterized with photoluminescence (PL) time-resolved spectroscopy and the space charge limited current (SCLC) method. Shorter PL time constants are obtained for the samples with only Cs, while longer PL decays are measured for the perovskites containing additional Gua cation. The SCLC measurements reveal a larger density of trap states in the Cs _x MA_1–x PbI₃ perovskites compared to the MAPbI₃ material. The PSCs fabricated with the different mixed cation Cs _x Gua _y MA_1–x–y PbI₃ perovskites reveal a good correlation with the measured optoelectronic properties. The power conversion efficiency (PCE) improves from an average value of 18.6% for the MAPbI₃ to a value of 20.0% for the Cs_0.05Gua_0.05MA_0.90PbI₃ perovskite with a champion cell delivering 21.2%. On the opposite, the PCE decreases to a value of 17.3% for the double cation perovskite with Cs.

Herein, it is described how semitransparent perovskite solar cells can be adapted to cope with specific and quite different requirements both for building integration and tandem photovoltaics. Clear guidelines for a rigorous device design based on “fitness-for-purpose” criteria are provided, together with some perspectives for future development by scanning the main challenges and issues to be addressed before commercialization.

Over the past decade, halide perovskite systems have captured widespread attention among researchers since their exceptional photovoltaic (PV) performance is disclosed. The unique combination of optoelectronic properties and solution processability shown by these materials has enabled perovskite solar cells (PSCs) to reach efficiencies higher than 25% at low fabrication costs. Moreover, PSCs display enormous potential for modern unconventional PV applications, since they can be made lightweight, semitransparent (ST), and/or flexible by means of appropriate design strategies. In particular, by enabling transparency and high efficiency simultaneously, ST-PSCs hold great promise for future versatile utilization in the context of building-integrated PVs (BIPVs) or as top cells to be coupled with conventional lower-bandgap bottom cells in tandem PV devices. The present review aims to provide a detailed overview of latest research about ST-PSCs for BIPVs and tandems, by critically reporting on the most updated and effective design strategies in view of these two possible future applications. The differences and similarities between the available approaches are punctually highlighted, emphasizing the importance of a rigorous application-orientated ST-PSC design. Finally, the main challenges and issues about device design, operation, and stability that need to be addressed before commercialization are thoroughly scanned.

Herein, the authors demonstrate the use of bulky-sized, trifluoromethyl-group (CF₃) bearing benzylammonium iodide (CF₃BZA-I) and bromide (CF₃BZA-Br) molecules as surface passivators for formamidium-methylammonium-based perovskite films. CF₃BZA-I/Br passivated perovskite films exhibit larger grain size, lesser surface defects, and hydrophobic surface. The champion perovskite solar cell achieves an efficiency of ≈20.8% with significantly improved air- and photostability.

Solution-processed perovskite films are rich in surface defects and grain boundaries, which limits their performance and stability in photovoltaic application. Surface passivation using bulky organic cations can effectively reduce the surface defects of a perovskite film without affecting its fundamental properties. Herein, the use of hydrophobic bulky aromatic molecules, namely 4-trifluoromethyl-benzylammonium iodide/bromide (CF₃BZA-I/Br), as defect-passivators to heal the surface defects and grain boundaries of perovskite films is introduced. Owing to the presence of the trifluoromethyl (CF₃) moieties, CF₃BZA-I/Br-passivated perovskite films exhibit a hydrophobic surface with significantly fewer grain boundaries. By suppressing the surface and interfacial imperfections, CF₃BZA-Br-treated perovskite solar cells achieve an outstanding power conversion efficiency (PCE) of 20.75%. The PCE improvement originates mainly from the reduction of trap states and nonradiative carrier recombination. The ultrathin hydrophobic barrier layer formed after passivation also shields the perovskite film surface from moisture ingress and environmental degradation, leading to improved stability of the devices. By optimizing the passivation conditions, the bulky CF₃BZA-I/Br molecules could be the ideal defect passivators, with versatile applications in a wide variety of perovskite optoelectronics.

The acetate (Ac⁻) ions occupy lattice sites in the process of nucleation and crystallization of the perovskite, which effectively promotes the entry of formamidinium (FA⁺) into the lead halide octahedra to stabilize the α-phase of FAPbI₃. The solar cell based on the α-FAPbI₃ film presented a power conversion efficiency of 21.24% with negligible hysteresis.

The α-phase formamidinium lead triiodide (α-FAPbI₃)-based perovskite solar cells (PSCs) exhibit potential high efficiency due to their narrow bandgap, but the fabrication of a stable α-FAPbI₃ film still is challenging. Herein, a strategy is devised to achieve a stable α-FAPbI₃ film, in which lead acetate (PbAc₂) is added to the perovskite precursor solution. The Ac⁻ ions are involved in the formation of the lead halide octahedra, which effectively promotes the entry of FA⁺ into the lead halide octahedra to stabilize the α-phase of FAPbI₃. Furthermore, the Ac⁻ will gradually leave during the annealing process, thus the addition of PbAc₂ cannot introduce other components in the FAPbI₃. The crystallinity and crystal orientation of the perovskite films are also improved by the PbAc₂ additive to obtain low trap density films, leading to an increase in charge carrier collection. The champion solar cell based on the α-FAPbI₃ film presented a power conversion efficiency (PCE) of 21.24% with negligible hysteresis. After 500 h of storage under ambient conditions, the devices still maintained more than 90% of their initial efficiency.

This work concentrates on electron transport layer (ETL) and hole transport layer (HTL) free inverted perovskite solar cells. It is observed that eliminating the HTL is most critical for photovoltaic performance, compared with ETL-free and fully inverted solar cell configurations.

The selective contacts in perovskite solar cells play a major role in solar cell (SC) performance and optimization. Herein, the inverted architecture is focused on, where systematically the electron transport layer (ETL) and the hole transport layer (HTL) from the SC structure are eliminated. Three main architectures of the SCs are studied: a fully inverted structure, an ETL-free structure, and a HTL-free structure. Cathodoluminescence and photoluminescence are measured on various architectures, revealing the electron and hole injection efficiency from the perovskite to selective contacts. Moreover, surface voltage spectroscopy shows the type and the band-edge transition of these layers. Finally, the photovoltaic (PV) performance of different SCs shows that eliminating the HTL is most critical for PV performance, compared with ETL-free and fully inverted SC configurations. Current−voltage hysteresis curves prove that efficient selective contacts are essential to eliminate this phenomenon. Measuring the ideality factor shows that the dominant mechanism in ETL-free SCs is surface recombination, whereas in the other cases, it is Shockley–Reed–Hall recombination. This work provides knowledge about the functionality of methylammonium lead iodide as an electron conductor and as a hole conductor.

Photovoltaic performance of perovskite solar cells (PSCs) based on low-temperature TiO₂ has not yet reached the mainstream level. Direct doping of alkali metal chloride into water-based TiO₂ is found to effectively improve the charge transport and extraction capabilities. The planar PSCs with NaCl-doped TiO₂ demonstrate a record efficiency of 23.15%, exhibiting a 4100 h storage stability.

Abstract

TiO₂ is one of the most broadly employed electron transport materials in n-i-p structure perovskite solar cells (PSCs). Low-temperature non-hydrolyzed sol–gel method is developed to prepare TiO₂ in order to simplify the fabrication process and match with the planar structure PSCs. Conventional low-temperature TiO₂ film using organic solvents as dispersants makes direct doping challenging due to limited solubility. Here, a newly developed water-based TiO₂ solution is directly doped with different alkali chlorides, resulting in better conductivity, compatible energy level matching, and enhanced charge extraction in terms of electron transport layer (ETL) for PSCs. As a result, a power conversion efficiency of 23.15% is achieved based on NaCl-doped TiO₂ with competitive storage stability and light stability. The water-based TiO₂ ETL for more general doping of various solutes opens up a new avenue for environmental-friendly manufacturing superior ETL toward high-efficiency and stable perovskite photovoltaic devices.

The advancement of organic photovoltaics has been significantly aided by the emergence of near-infrared (NIR) materials, and they are also able to satisfy the varied criteria for various types of organic photovoltaic device architectures. Furthermore, the absorption window is the most fundamental criterion for developing novel NIR organic photoelectric materials.

Abstract

Near-infrared (NIR)-absorbing organic semiconductors have opened up many exciting opportunities for organic photovoltaic (OPV) research. For example, new chemistries and synthetical methodologies have been developed; especially, the breakthrough Y-series acceptors, originally invented by our group, specifically Y1, Y3, and Y6, have contributed immensely to boosting single-junction solar cell efficiency to around 19%; novel device architectures such as tandem and transparent organic photovoltaics have been realized. The concept of NIR donors/acceptors thus becomes a turning point in the OPV field. Here, the development of NIR-absorbing materials for OPVs is reviewed. According to the low-energy absorption window, here, NIR photovoltaic materials (p-type (polymers) and n-type (fullerene and nonfullerene)) are classified into four categories: 700–800 nm, 800–900 nm, 900–1000 nm, and greater than 1000 nm. Each subsection covers the design, synthesis, and utilization of various types of donor (D) and acceptor (A) units. The structure–property relationship between various kinds of D, A units and absorption window are constructed to satisfy requirements for different applications. Subsequently, a variety of applications realized by NIR materials, including transparent OPVs, tandem OPVs, photodetectors, are presented. Finally, challenges and future development of novel NIR materials for the next-generation organic photovoltaics and beyond are discussed.

Phthalide and 1-Iodooctadecane synergistic optimization successfully passivates cation and anion defects, effectively mitigates carrier non-radiative recombination and consequently results in perovskite solar cells high-efficiency of 22.27% and excellent stability.

Abstract

The carrier non-radiative recombination and instability of device caused by the inherent defects are main factors limiting development of perovskite solar cells (PSCs). During the fabrication process of a PSC device, perovskite films often produce Pb⁰ and I⁰ defects. This paper reports a strategy for synergistic optimization of perovskite films by defects passivation and surface modification. The doping of phthalide (PT) in the Pb-rich (CH(NH₂)₂)_1−x(CH₃NH₃)_xPbI₃ film can passivate lead cation defects, and the modification of 1-iodooctadecane (1-IO) can reduce halogen anion defects and improve stability of PSCs owing to its hydrophobicity. The PT and 1-IO optimized device achieves a power conversion efficiency (PCE) of 22.27%. The optimized PSCs remain 93.2% of the initial PCE when placed in air environment (relative humidity of 10%, 25 °C) more than 70 days. The PT and 1-IO synergistic optimization provides a novel strategy for improving the performance and stability of PSCs.

Here, an alternative additive (propylammonium chloride (PACl)) is reported to replace the commonly used methylammonium chloride for FAPbI₃ perovskite. The perovskite solar cell based on the PACl additive exhibits a power conversion efficiency of 22.22%, which is one of best efficiencies among the MA-free and Br-free perovskite solar cells.

Abstract

To achieve high efficiency perovskite solar cells (PSCs) based on α-phase formamidinium lead iodide (FAPbI₃), addition of methylammonium chloride (MACl) in the precursor solution is commonly used, mainly because of phase stability and improvement of grain size and crystallinity. However, the instability of MA in the perovskite limits the device long-term stability. In this report, n-propylammonium chloride (PACl) is proposed as an alternative to MACl for more stable and efficient FAPbI₃-based PSCs. Perovskite grain size is increased after addition of PACl. Unlike the MA cation, the propylammonium cation passivates the grain boundary rather than being incorporated into the perovskite lattice due to larger ionic size, which minimizes the change in bandgap. Carrier lifetime is significantly increased by more than five times from 405 to 2110 ns with the PACl additive with negligible trap-mediated recombination, while only four times longer carrier lifetime is observed by MACl additive. As a result, a power conversion efficiency over 22.2% is achieved by 20 mol% PACl additive, which is one of the best efficiencies among the MA-free and Br-free PSCs. In addition, stability against moisture is much better for PACl than for MACl due to an in situ formed barrier at the bulk perovskite.

In this study it is reported an electroluminescent solar cell using CsPbI₃ quantum dots (QDs) via solid-state-ligand exchange process using organic ligand triphenyl phosphite; the device achieves a champion efficiency of 15.21%, and an overall electric power to light conversion efficiency of 3.80% in red light-emitting diode function, a record value for QD photovoltaics.

Abstract

All-inorganic CsPbX₃ (X = Cl, Br, I, or mixed halides) perovskite quantum dots (QDs) exhibit tunable optical bandgaps and narrow emission peaks, which have received worldwide interest in the field of both photovoltaics (PVs) and light-emitting diodes (LEDs). Herein, it is reported a discovery that CsPbI₃ perovskite QD solar cell can simultaneously deliver high PV performance and intense electroluminescence. In specific, the multifunctional CsPbI₃ QD film is fabricated through a simple yet efficient solid-state-ligand exchange process using a tailored organic ligand triphenyl phosphite (TPPI). The function of QD surface manipulation using TPPI here is proven to be twofold, balancing the carrier transport and effectively passivating the QD surface to produce conductive and emissive QD film. The CsPbI₃ perovskite QD solar cell delivers a champion efficiency of 15.21% with improved open circuit voltage and high fill factor. Concurrently functioning as a red LED, the CsPbI₃ perovskite QD solar cell outputs electric power to light conversion efficiency approaching 4%, a record value for QD electroluminescent PVs. The results here indicate that these versatile perovskite QDs may be a promising candidate for fabricating multifunctional optoelectronic devices.

The authors report a novel strategy co-modulation of crystallization and co-passivation of defects for FAPbI₃ perovskite solar cell, which gives a high PCE of 21.6% for the modified PSC (only 16.5% for the control device).

Abstract

Enhancing crystallinity, passivating the grain boundary and interfacial defects have been validated to be critical for improving the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a synergetic co-modulation and co-passivation strategy is proposed to simultaneously enhance crystallinity and passivate the grain boundary and surface defects of FAPbI₃ based PSCs. The 4-fluoro-phenethylammonium iodide (4-F-PEAI) added in precursor solution and poly (9-vinylcarbazole) (PVK) added in antisolvent can jointly modulate the crystallization of FAPbI₃ films. The 4-F-PEAI-derived 2D perovskite, which is spontaneously formed at the grain boundaries of FAPbI₃, can passivate the defects effectively. In the meantime, PVK left on top of a FAPbI₃ layer can passivate the surface defects and meanwhile function as an interfacial barrier layer between FAPbI₃ and hole transport layer (HTL) to mitigate the detrimental interfacial charge recombination. With the holistic benefit of the enhanced crystallinity, reduced defects and trap sites, and mitigated non-radiative recombination and suppressed ion migration, the encouraging PCEs up to 21.6% is achieved for the resulting modified PSCs. Additionally, this strategy endows the device with notably enhanced operational stability under continuous exposure to illumination, with more than 84% of the initial PCE being maintained after continuous illumination for 800 h.

A 3D optical simulation study is reported that predicts average visible transmission and ideal J _SC values of semi-transparent organic photovoltaics (ST-OPVs) with porous silver nanowire top electrodes, thereby leading to the highest light utilization efficiency value in ST-OPVs reported to date.

Abstract

A key factor in improving semi-transparent organic photovoltaics (ST-OPVs) performance is achieving high light utilization efficiency (LUE). However, device performance can also be limited by the lack of understanding of light transmission and reflection within the device architecture, and the transmission of the top electrode in particular. Here, highly efficient ST-OPVs are reported via the rational design of silver nanowire (Ag NW) top electrodes via 3D optical simulation. Due to its careful consideration for the ST-OPV of the effect of the Ag NW networking structure, estimated average visible transmission (AVT) and ideal short-circuit current density values from 3D optical simulation closely match those from actual measurements. Optimized ST-OPVs with Ag NW porosity of 20% and active layer thickness of 150 nm exhibit LUE of 4.15% with a power conversion efficiency of 9.7% and AVT of 42.82%. This work achieves a record-high LUE in ST-OPVs reported to date and the first report introducing a 3D optical simulation study.

Unprecedently bright, efficient, and stable quantum dot light-emitting diodes (QLEDs) are presented by multilateral approaches, including appropriate modification of the QD structure and optimization of the device architecture, via resolving heat-related degradation, enhancing light-outcoupling, and controlling the excitonic states precisely, which expands the applications of QLEDs as a light source.

Abstract

Quantum dot light-emitting diodes (QLEDs) are one of the most promising candidates for next-generation displays and lighting sources, but they are barely used because vulnerability to electrical and thermal stresses precludes high brightness, efficiency, and stability at high current density (J) regimes. Here, bright and stable QLEDs on a Si substrate are demonstrated, expanding their potential application boundary over the present art. First, a tailored interface is granted to the quantum dots, maximizing the quantum yield and mitigating nonradiative Auger decay of the multiexcitons generated at high-J regimes. Second, a heat-endurable, top-emission device architecture is employed and optimized based on optical simulation to enhance the light outcoupling efficiency. The multilateral approaches realize that the red top-emitting QLEDs exhibit a maximum luminance of 3 300 000 cd m⁻², a current efficiency of 75.6 cd A⁻¹, and an operational lifetime of 125 000 000 h at an initial brightness of 100 cd m⁻², which are the highest of the values reported so far.

The formamidinium-based perovskite films prepared in the low humidity condition possess less pinholes and defects and exhibit better device performances than those prepared in the moisture-free condition. The defects in the perovskite films are continuously healed during thermal annealing through the interaction between water molecules and perovskite.

Abstract

Formamidinium (FA)-based perovskite material holds great potential to deliver highly efficient commercial solar cells. However, the FA-based perovskite films are commonly processed under a strictly controlled environment, which would eventually hinder their way to commercialization. Herein, a systematic study is conducted to investigate the sequential deposition of FA-based perovskite films that are annealed under ambient conditions. Unexpectedly, the films prepared in low humidity condition possess less pinholes and defects and exhibit better device performances than those prepared in the moisture-free condition. A series of in situ and ex situ investigations are conducted which reveal defects in perovskite films are continuously healed during the film annealing process under the humid condition. This extraordinary effect is attributed to the interaction between water molecules and perovskite. The current study should shed light on the ambient fabrication of FA-based perovskite solar cells and foster their real-world applications.

Through a charge-transfer doping strategy to tune the carrier-type, P/N homojunction CsPbI₃ perovskite QD solar cells are demonstrated; the P/N homojunction significantly improves the carrier dynamic process and outputs record high efficiency in a QD active layer with thickness over 1 µm, demonstrating great potential for the future printing manufacturing of QD PVs.

Abstract

The solution-processed solar cells based on colloidal quantum dots (QDs) reported so far generally suffer from poor thickness tolerance and it is difficult for them to be compatible with large-scale solution printing technology. However, the recently emerged perovskite QDs, with unique high defect tolerance, are particularly well-suited for efficient photovoltaics. Herein, efficient CsPbI₃ perovskite QD solar cells are demonstrated first with over 1 µm-thick active layer by developing an internal P/N homojunction. Specifically, an organic dopant 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6TCNNQ) is introduced into CsPbI₃ QD arrays to prepare different carrier-type QD arrays. The detailed characterizations reveal successful charge-transfer doping of QDs and carrier-type transformation from n-type to p-type. Subsequently, the P/N homojunction perovskite QD solar cell is assembled using different carrier-type QDs, delivering an enhanced power conversion efficiency of 15.29%. Most importantly, this P/N homojunction strategy realizes remarkable thickness tolerance of QD solar cells, showing a record high efficiency of 12.28% for a 1.2 µm-thick QD active-layer and demonstrating great potential for the future printing manufacturing of QDs solar cells.