Non-radiative Recombination Losses Research Articles

Reducing charge-recombination losses in photovoltaic cells by spontaneous reconstruction of n/p homojunction in a monolithic perovskite film using black phosphorus nanosheets

Trap-assisted charge recombination and interfacial charge recombination have limited further improvements in the efficiency and stability of perovskite solar cells. We construct a novel two-dimensional (2D) black phosphorus nanosheet (BP NS)-modified perovskite model that utilizes an upgraded additive post-processing technique to introduce 2D BP NSs, comprising multiple functional groups and carrying a high charge mobility and high work function, into the absorber during Ostwald ripening. 2D BP NSs, while passivating grain boundaries and surface defects, successfully induced the in-situ formation of an intriguing n/p homojunction structure between the underlying bulk and the top in a monolithic perovskite film, i.e., a graded n/p-PVK-BP absorber. This resulted in the synergistic advantages of expanding the built-in electric field to facilitate the oriented transfer of photogenerated carriers, optimizing the energy level alignment, and minimizing the hole injection barrier at the perovskite/hole transporting layer interface, thereby accelerating the selective extraction/collection of interfacial charges and synchronously reducing nonradiative and interfacial charge recombination losses. The 2D BP NSs anchored at the grain boundaries and surface of p-type perovskite form a “fast path” for hole migration, achieving carrier transport balance at the top and bottom interfaces. The optimized n/p-PVK-BP device achieved an efficiency of 23.22 %, with negligible hysteresis. Owing to the synergistic effects of the various advantages of the graded n/p-PVK-BP homojunction absorber, the unencapsulated device exhibited good long-term storage and operational stability, providing potential for commercial conversion of perovskite-based optoelectronics. This work provides a simple homojunction structure design and performance optimization strategy for the simultaneous reduction of trap-assisted charge recombination and interfacial charge recombination losses and provides new insights for the development of more efficient and stable perovskite photovoltaic applications.

Effect of solvent annealing in the growth of MAPbI3 for perovskite solar cells

Perovskite solar cell (PSC) is recognized as one of the most promising solar cells because of a drastic enhancement in photovoltaic performance. Numerous studies showed that grain size in a perovskite layer plays a vital role in determining the PSC performance. It is expected that the large-sized grains are beneficial for PSCs due to less grain boundaries and reduced non-radiative recombination losses. The perovskite grains can be enlarged by many methods including solvent annealing approach in which an as-prepared perovskite film is annealed under dimethylformamide (DMF) vapor environment. In this work, the effect of the amount of DMF and annealing time on the surface morphology and photovoltaic parameters of PSCs were investigated and compared to the pristine devices. It was found from the inspection with FESEM images that perovskite grains were significantly enlarged as DMF was introduced. As a result, the overall photovoltaic parameters of DMF-based devices are superior to that of the pristine devices. The best device obtained using two rounds of 50 µL DMF for 15 minutes annealing shows maximum power conversion efficiency of 18.0% compared to 15.3% of the pristine devices.

Rationally Tailoring Chiral Molecules to Minimize Interfacial Energy Loss Enables Efficient and Stable Perovskite Solar Cells Using Vacuum Flash Technology.

Facing the defects and energy barrier at the interface of perovskite solar cells, we propose a chiral molecule engineering strategy to simultaneously heal interfacial defects and regulate interfacial energy band alignment. S-ibuprofen (S-IBU), R-ibuprofen (R-IBU), and racemic ibuprofen (rac-IBU) are used to post-treat perovskite films. rac-IBU molecules possess the strongest anchoring on the surface of perovskites among all chiral molecules, translating into the best defect passivation effect. The hydrophobic isobutyl group and benzene ring could increase the film moisture resistance ability. Due to reduced interfacial defects and interfacial energy barrier, rac-IBU enables efficient devices with a maximum efficiency exceeding 24% based on vacuum flash technology without antisolvents. The encapsulated rac-IBU-modified device could maintain 90% of its initial performance after 1040 h of continuous maximum power point tracking. This work provides a feasible route to minimize interfacial nonradiative recombination losses by controlling spatial conformation via rational chiral molecule engineering.

Quantifying Nonradiative Recombination and Resistive Losses in Perovskite Photovoltaics: A Modified Diode Model Approach

Pinpointing the origin of inefficiency can expedite the process of optimizing the efficiency of perovskite photovoltaics. However, it is challenging to discern and quantify the different loss pathways in a complete perovskite photovoltaic device under operational conditions. To address this challenge, a modified diode (MD) model is proposed that can quantify bulk/interface defect‐assisted recombination and series/shunt resistive losses. By adopting drift‐diffusion simulation as the benchmark, the physical meanings of the MD model parameters are explored and the performance of the model for simulation parameters spanning many orders of magnitude is evaluated. The evaluation shows that in most practical cases, the proposed model can accurately quantify all the aforementioned losses, and in some special cases, it is possible to identify the predominant loss pathway. Moreover, the MD model is applied to lab‐produced devices (based on Cs0.05FA0.95PbI3 perovskites), demonstrating its effectiveness in quantifying entangled losses in practice. Finally, a set of guidelines for applying the MD model and interpreting the results is provided.

Crystallization Regulation by Self‐Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells

AbstractIt is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1‐Dodecyl‐3‐methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC‐modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.

Crystallization Regulation by Self-Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells.

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.

Bimolecularly passivated interface enables efficient and stable inverted perovskite solar cells

Compared with the n-i-p structure, inverted (p-i-n) perovskite solar cells (PSCs) promise increased operating stability, but these photovoltaic cells often exhibit lower power conversion efficiencies (PCEs) because of nonradiative recombination losses, particularly at the perovskite/C 60 interface. We passivated surface defects and enabled reflection of minority carriers from the interface into the bulk using two types of functional molecules. We used sulfur-modified methylthio molecules to passivate surface defects and suppress recombination through strong coordination and hydrogen bonding, along with diammonium molecules to repel minority carriers and reduce contact-induced interface recombination achieved through field-effect passivation. This approach led to a fivefold longer carrier lifetime and one-third the photoluminescence quantum yield loss and enabled a certified quasi-steady-state PCE of 25.1% for inverted PSCs with stable operation at 65°C for >2000 hours in ambient air. We also fabricated monolithic all-perovskite tandem solar cells with 28.1% PCE.

Synergetic Regulation of Interface Defects and Carriers Dynamics for High-Performance Lead-Free Perovskite Solar Cells.

Severe nonradiative recombination and open-circuit voltage loss triggered by high-density interface defects greatly restrict the continuous improvement of Sn-based perovskite solar cells (Sn-PVSCs). Herein, a novel amphoteric semiconductor, O-pivaloylhydroxylammonium trifluoromethanesulfonate (PHAAT), is developed to manage interface defects and carrier dynamics of Sn-PVSCs. The amphiphilic ionic modulators containing multiple Lewis-base functional groups can synergistically passivate anionic and cationic defects while coordinating with uncoordinated Sn2+ to compensate for surface charge and alleviate the Sn2+ oxidation. Especially, the sulfonate anions raise the energy barrier of surface oxidation, relieve lattice distortion, and inhibit nonradiative recombination by passivating Sn-related and I-related deep-level defects. Furthermore, the strong coupling between PHAAT and Sn perovskite induces the transition of the surface electronic state from p-type to n-type, thus creating an extra back-surface field to accelerate electron extraction. Consequently, the PHAAT-treated device exhibits a champion efficiency of 13.94% with negligible hysteresis. The device without any encapsulation maintains 94.7% of its initial PCE after 2000h of storage and 91.6% of its initial PCE after 1000h of continuous illumination. This work provides a reliable strategy to passivate interface defects and construct p-n homojunction to realize efficient and stable Sn-based perovskite photovoltaic devices.

Crystallization Enhancement and Ionic Defect Passivation in Wide‐Bandgap Perovskite for Efficient and Stable All‐Perovskite Tandem Solar Cells

AbstractBy integrating wide‐bandgap (WBG) and narrow‐bandgap perovskites, monolithic all‐perovskite tandem solar cells have garnered significant attention as a prospective strategy for surpassing the efficiency limits of single‐junction cells. However, the WBG subcells, which significantly impact the performance and operational stability of all‐perovskite tandem solar cells, face notable challenges associated with pronounced nonradiative recombination losses and limited film photostability. Here, an efficient method is reported by adding potassium hypophosphite into the perovskite precursor solution to simultaneously regulate crystallization and passivate ionic defects in WBG perovskites. This approach results in high‐quality perovskite films and significantly improves the performance and photostability of WBG perovskite solar cells. The single‐junction devices with a 1.79 eV bandgap achieve a champion power conversion efficiency (PCE) of 20.06% with an open‐circuit voltage of 1.32 V. The devices retain ≈96% of their initial PCE following 913 h of continuous AM 1.5 G illumination. With these WBG perovskite subcells, monolithic all‐perovskite tandem solar cells are fabricated with an efficiency of 26.08%.

Perovskite solar cell technology scaling‐up: Eco‐efficient and industrially compatible sub‐module manufacturing by fully ambient air slot‐die/blade meniscus coating

AbstractThe efficiency gap between perovskite (PVSK) solar sub‐modules (size ≥200 cm2) and lab scale cells (size ˂1 cm2) is up to 36%. Moreover, the few attempts present in the literature used lab‐scale techniques in a glove‐box environment, reducing its compatibility for further product industrialization. Here, we report a PVSK sub‐module (total area 320 cm2, aperture area 201 cm2, 93% geometrical fill factor [GFF]) fabricated in ambient air by hybrid meniscus coating techniques assisted by air and green antisolvent quenching method. To suppress nonradiative recombination losses, improve carrier extraction and control the PVSK growth on such a large surface, we adopted phenethylammonium iodide (PEAI) passivation and PVSK solvent addiction strategies. The high homogeneous and reproducible layers guarantee an efficiency of 16.13% (7% losses with respect to the small area cell and zero losses with respect to the mini‐modules) and a stability of more than 3000 h according to International Summit on Organic PV Stability, dark storage/shelf life in ambient (ISOS‐D‐1). The sustainability of used methods and materials is demonstrated by the life cycle assessment. The scale‐up operation allows for strong impact mitigation in all the environmental categories and more efficient consumption of the resources. Finally, the economic assessment shows a strong cost reduction scaling from mini‐ to sub‐module (about 40%).

Buried interfacial modification in inverted perovskite solar cells with mercaptoethylamine

Poly (bis (4-phenyl) (2,4, 6-trimethylamine) amine) (PTAA) is widely used as a hole transport layer (HTL) in inverted perovskite solar cells (PSCs). However, the high hydrophobicity and non-radiative recombination losses of PTAA greatly limit the repeatability and photoelectric performance of PSCs. In this study, mercaptoethylamine (MEA), containing sulfhydryl groups, is proposed to fill the interface defect between PTAA and the perovskite layer, significantly improving the wettability of PTAA film and resulting in a more uniform perovskite layer deposition when compared with the common short carbon chain, propylamine (PA). By evaluating the energy level alignment and perovskite crystal growth in CsFA-based PSCs, it is demonstrated that MEA effectively eliminates lead (Pb) defects at the buried interface of perovskite films, suppresses trap-assisted carrier recombination, and extends the operational lifespan of PSCs. The results show that the power conversion efficiency of the p-i-n inverted CsFA-based photovoltaic device, reaches 22% after MEA optimization, and the unpackaged device maintains 97% of its initial efficiency under standard illumination after 300 h. Furthermore, when MEA was introduced to optimize the buried interface of CsFAMA-based perovskite films, the device achieved a power conversion efficiency of 23.18%. This work provides a promising approach for improving the performance and stability of perovskite solar cells through organic cation modification at the PTAA/perovskite interface.

Energy Band Alignment at p–n Heterojunction Interface in CZTSSe Solar Cells with Novel ZnMgO Buffer Layer

By substituting Zn1−xMgxO (ZMO) for the conventional CdS buffer layer, the CZTSSe solar cells with the efficiency of 11.2% are obtained herein, which can be attributed to the conduction band regulation in the heterojunction. An appropriate conduction band offset (CBO) value can effectively reduce nonradiative recombination loss of charge carriers at the interface, thereby improving the open‐circuit voltage (Voc). Herein, ZMO buffer layer with the optical bandgap ranging from 3.34 to 3.90 eV is applied to enhance the CBO in the heterojunction from 0.14 to 0.72 eV. The ZMO‐buffered solar cells exhibit higher Voc and short‐current density (Jsc) compared to CdS‐buffered cells. The optimal efficiency of 11.2% is obtained in CZTSSe solar cell with the CBO of 0.27 eV, Jsc of 39.0 mA cm−2, fill factor of 69.6%, and Voc of 412 mV.

Multifunctional Self-Assembled Ionic Liquid Modified Rigid and Flexible Substrates for Efficient Simple-Structured Perovskite Solar Cells.

The advancement of electron transport layer (ETL)-free perovskite solar cells (PSCs) is crucial for the commercialization of PSCs. At present, the slow electron extraction and significant carrier recombination, related to the energy-level alignment at the FTO/perovskite interface, restrict the performance of ETL-free PSCs. The facile modification of bottom electrodes is pivotal for tackling these issues and stimulating the photovoltaic potential of perovskite. Herein, a cost-competitive and neoteric 1-hydroxyethyl-3-methylimidazolium chloride, [HOEtMIM]Cl, ionic liquid is employed to modify the surface of rigid and flexible electrodes, and thus enable an energetically well-aligned interface with perovskite layer via the electric dipole effects. The resulting barrier-free FTO/perovskite contact can tremendously ameliorate the electron extraction and collection, with mitigated nonradiative interfacial carrier recombination loss. Additionally, the lone pair on the nitrogen of the imidazole group passivates the surface defects of perovskite layers, and the chloride anion plays a role in the crystallinity improvement of perovskite. Leveraged by the [HOEtMIM]Cl modification, the resulting ETL-free rigid and flexible devices deliver an outstanding power conversion efficiency of 19.60 % and 15.57 %, along with the ameliorated hysteresis and long-term tenability. This finding highlights the drastic potential of the engineered [HOEtMIM]Cl in manufacturing stable and high-performance ETL-free PSCs for their scaled-up production.

Inhibiting Nonradiative Recombination and Scattering Losses via Ultrafast Pulse Irradiation for Enhanced Perovskite Lasing

Inhibiting Nonradiative Recombination and Scattering Losses via Ultrafast Pulse Irradiation for Enhanced Perovskite Lasing

Minimizing Buried Interface Nonradiative Recombination Losses by Multifunctional Chemical‐Bridging Molecules Enables Efficient Perovskite Solar Cells

Minimizing the buried interface carrier nonradiative recombination loss has been a great challenge in the field of perovskite solar cells. Herein, a multifunctional chemical‐bridging strategy is reported where the α‐cyano‐4‐hydroxycinnamic acid (CHCA) molecule with multiple functional groups including −COOH, −OH, and −C ≡ N is adopted to manipulate buried interface. Due to simultaneous interaction of multiple groups in CHCA with SnO2 and perovskite layers, interfacial contact is ameliorated. The double‐sided chemical anchoring by CHCA enables interfacial defect passivation, residual tensile strain mitigation, reduced interfacial energy barrier, and improved perovskite crystallization. Through this ingenious chemical‐linking strategy, the power conversion efficiency is much increased from 21.26% to 23.02%, which is owing to much suppressed buried interface nonradiative recombination. The unsealed modified devices demonstrate enhanced moisture stability, degrading by less than 6% after 1500 h of aging under the relative humidity range of 15–20%. In this work, a way for minimizing buried interfacial nonradiative recombination losses through the rational design of versatile chemical‐bridging molecules with the synergy of multiple functional groups is provided.

Green synthesis of highly luminescent CsPbBr3 quantum dots through silica coating and post-treatment with ligands

All-inorganic perovskite quantum dots (PQDs) have received considerable attentions due to their fascinating optical properties. However, the mainstream preparation methods rely on toxic solvents, raising significant environmental and safety concerns. In this work, ethyl acetate was chosen as the environmentally friendly anti-solvent to prepare silica-coated CsPbBr3 PQDs using a aminoalkoxysilane-assisted reprecipitation–encapsulation method. The as-prepared PQDs exhibited tunable emission wavelength and a medium photoluminescence quantum yield (PLQY) of 60%. Furthermore, CsPbBr3 PQDs were post-treated by different ligands with the aim of passivating surface defects. This strategy successfully mitigated the presence of surface defects and minimized non-radiative recombination losses in PQDs. As a result, the PLQY (achieving up to 73%) and stability of PQDs were substantially enhanced (luminescence stability improved by about 40% under the same test conditions). Our studies offer a novel approach for the environmentally friendly large-scale production of PQDs, opening up new possibilities for their practical applications.

Refining interface compatibility and carrier management via π-π conjugated stacking for efficient and stable perovskite solar cells based on low-temperature processing

ABSTRACT Deficiencies and instability in the ETL, perovskite layer, or their interface contribute to carrier nonradiative recombination losses. To address these issues, we propose an electron collection and injection optimisation strategy that focuses on enhancing the compatibility and charge transfer performance at the ETL-perovskite interface. Our approach involves low-temperature modification TiO2 with pyrimidine-2-carboximidamide acetate (PCA) through π-π stacking, reducing the surface energy and improving the interfacial compatibility. At the same time, a stable organic–inorganic hybrid layer is formed with lead iodide (PbI2) below the perovskite layer. Additionally, we demonstrate long-term ambient stability, with the PSCs retaining approximately 90% of their initial PCE after 100 days. We also fabricate large-area modules, achieving an efficiency of 19.53% with an active area of 36.41 cm2. Highlights The introduction of the π-π stacking multifunctional molecule PCA through a low-temperature process to modify TiO2 film enhances the stability and performance of perovskite solar cells. This novel approach improves interfacial compatibility and reduces defects at the interface, enabling vertically aligned crystal growth of perovskite and increasing the interfacial contact area. By effectively removing two types of Hydroxyl groups over the low-temperature TiO2 film through multiple surface chemical reactions, the strategy mitigates nonradiative recombination, leading to reduced energy losses and improved performance in both small and large-area perovskite solar cell modules.

Synergistic passivation of high stability CsPb(Br/I)3 perovskite quantum dots with double ligands for WLEDs

The all-inorganic perovskite CsPbI3 quantum dots are difficult to achieve pure red stable luminescence due to their poor lattice thermodynamic stability and non-radiative recombination loss caused by surface halide vacancies. Therefore, the pure red perovskites are usually achieved by mixing the composition of halides (Br and I). In this work, CsPb(Br/I)3 quantum dots (QDs) were synthesized by the hot-injection method under the synergistic effect of homophthalic acid (HA), 2-bromoethanesulphonic acid sodium salt (SBES), and oleylamine (OAm). By adjusting the molar ratio of passivates, the synergistic effect of multiple ligands can not only passivate the unliganded Pb2+-related defects on the surface of NCs, but also increase the formation energy of halide vacancies. Meanwhile, due to the bidentate structure of HA, smaller size of perovskites nanocrystals were obtained. Eventually, synergistic boost in device performance is achieved for color-by-blue white light-emitting diodes (WLEDs) with CIE coordinates of (0.3319, 0.3297) and have an external quantum efficiency (EQE) of 10.13%. This strategy paves an efficient way for improving the efficiency and stability of CsPb(Br/I)3 NCs.

Understanding and Suppressing Non-Radiative Recombination Losses in Non-Fullerene Organic Solar Cells.

Organic solar cells benefit from non-fullerene acceptors (NFA) due to their high absorption coefficients, tunable frontier energy levels, and optical gaps, as well as their relatively high luminescence quantum efficiencies as compared to fullerenes. Those merits result in high yields of charge generation at a low or negligible energetic offset at the donor/NFA heterojunction, with efficiencies over 19% achieved for single-junction devices. Pushing this value significantly over 20% requires an increase in open-circuit voltage, which is currently still well below the thermodynamic limit. This can only be achieved by reducing non-radiative recombination, and hereby increasing the electroluminescence quantum efficiency of the photo-active layer. Here, current understanding of the origin of non-radiative decay, as well as an accurate quantification of the associated voltage losses are summarized. Promising strategies for suppressing these losses are highlighted, with focus on new material design, optimization of donor-acceptor combination, and blend morphology. This review aims at guiding researchers in their quest to find future solar harvesting donor-acceptor blends, which combine a high yield of exciton dissociation with a high yield of radiative free carrier recombination and low voltage losses, hereby closing the efficiency gap with inorganic and perovskite photovoltaics.

One-dimensional scintillator film with benign grain boundaries for high-resolution and fast x-ray imaging.

Fast and high-resolution x-ray imaging demands scintillator films with negligible afterglow, high scintillation yield, and minimized cross-talk. However, grain boundaries (GBs) are abundant in polycrystalline scintillator film, and, for current inorganic scintillators, detrimental dangling bonds at GBs inevitably extend radioluminescence lifetime and increase nonradiative recombination loss, deteriorating afterglow and scintillation yield. Here, we demonstrate that scintillators with one-dimensional (1D) crystal structure, Cs5Cu3Cl6I2 explored here, possess benign GBs without dangling bonds, yielding nearly identical afterglow and scintillation yield for single crystals and polycrystalline films. Because of its 1D crystal structure, Cs5Cu3Cl6I2 films with desired columnar morphology are easily obtained via close space sublimation, exhibit negligible afterglow (0.1% at 10 ms) and high scintillation yield (1.2 times of CsI:Tl). We have also demonstrated fast x-ray imaging with 27 line pairs mm-1 resolution and frame rate up to 33 fps, surpassing most existing scintillators. We believe that the 1D scintillators can greatly boost x-ray imaging performance.