High-efficiency Perovskite Solar Cells Research Articles

SnSe2 Quantum Dots and Chlorhexidine Acetate Suppress Synergistically Non-radiative Recombination Loss for High Efficiency and Stability Perovskite Solar Cells.

Non-radiative recombination losses limit the property of perovskite solar cells (PSCs). Here, a synergistic strategy of SnSe2QDs doping into SnO2 and chlorhexidine acetate (CA) coating on the surface of perovskite is proposed. The introduction of 2D SnSe2QDs reduces the oxygen vacancy defects and increases the carrier mobility of SnO2. The optimized SnO2 as a buried interface obviously improves the crystallization quality of perovskite. The CA containing abundant active sites of ─NH2/─NH─, ─C═N, CO, ─Cl groups passivate the defects on the surface and grain boundary of perovskite. The alkyl chain of CA also improves the hydrophobicity of perovskite. Moreover, the synergism of SnSe2QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite. Benefiting from these advantages, the bulk and interface non-radiative recombination loss is greatly suppressed and thereby increases the carrier transport and extraction in devices. As a result, the best power conversion efficiency (PCE) of 23.41% for rigid PSCs and the best PCE of 21.84% for flexible PSCs are reached. The rigid PSC maintains 89% of initial efficiency after storing nitrogen for 3100 h. The flexible PSCs retain 87% of the initial PCE after 5000 bending cycles at a bending radius of 5 mm.

Alkyl Chains Tune Molecular Orientations to Enable Dual Passivation in Inverted Perovskite Solar Cells.

Nonradiative recombination losses occurring at the interface pose a significant obstacle to achieve high-efficiency perovskite solar cells (PSCs), particularly in inverted PSCs. Passivating surface defects using molecules with different functional groups represents one of the key strategies for enhancing PSCs efficiency. However, a lack of insight into the passivation orientation of molecules on the surface is a challenge for rational molecular design. In this study, aminothiol hydrochlorides with different alkyl chains but identical electron-donating (-SH) and electron-withdrawing (-NH3+) groups were employed to investigate the interplay between molecular structure, orientation, and interaction on perovskite surface. The 2-Aminoethane-1-thiol hydrochloride with shorter alkyl chains exhibited a preference of parallel orientations, which facilitating stronger interactions with the surface defects through strong coordination and hydrogen bonding. The resultant perovskite films following defect passivation demonstrate reduced ion migration, inhibition of nonradiative recombination, and more n-type characteristics for efficient electron transfer. Consequently, an impressive power conversion efficiency of 25% was achieved, maintaining 95% of its initial efficiency after 500 hours of continuous maximum power point tracking.

Two-dimensional phthalocyanine-based molecular additives realize efficient hole transport and enhanced ion immobilization for durable perovskite solar cells

Perovskite solar cells (PSCs) have demonstrated high promises in low-cost manufacture and outstanding power conversion efficiencies (PCEs), however, long-term operational stability has become the major obstacle challenging the scalable application of this technology. Although the state-of-the-art hole transport layer (HTL) based on Spiro-OMeTAD becomes the indispensable component in high-efficiency PSCs, the dopants in the HTLs cause severe stability issues of ion migration and phase segregation, all of which induce the degradation of HTLs in the aspects of film conductivity and microstructures. Here we rationally design a two-dimensional phthalocyanine-based molecular additive (TB-C8-Ni) for the HTLs in order to enhance the carrier transportation and immobilize the ions. The incorporation of [8-(4-tert-butylphenoxy)octyl]oxy alkyl units as the side groups in TB-C8-Ni is essential to increase the solubility and improve the HTL uniformity. The superior planar structure of TB-C8-Ni favors the hole transportation and suppresses the migration of lithium ion under the environmental stress, which achieves reliable HTLs and devices. Consequently, the devices based on TB-C8-Ni exhibit boosted open-circuit voltage and fill factor, delivering an increased efficiency from 20.93% to 22.34%. More importantly, the additive TB-C8-Ni in the HTLs reinforces the moisture stability of devices, enabling to maintain 90% of initial efficiency after 2300 h in air.

Ultrafine SnO2 colloids with enhanced interface quality for high-efficiency perovskite solar cells

Ultrafine SnO2 colloids with enhanced interface quality for high-efficiency perovskite solar cells

HALS-770 interlayer simultaneously block internal and external degradation paths of perovskite for stability and high efficiency perovskite solar cells

The stability of perovskite solar cells (PSCs) is a major problem limiting their application. Here, we proposed a feasible solution using bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (HALS-770) as top protection layer of perovskite. HALS-770 interlayer can not only improve the antioxidant ability of perovskite by removing superoxide (O2·-) with help of hindered amine groups, but also suppress the internal and external degradation path of perovskite due to the co-existence of hydrophilic and hydrophobic groups. Moreover, it can block volatilization of organic cation and the migration of Ag+ and I-, thus improve thermal stability of perovskite and alleviate destruction of Ag electrode. In addition, the heterocycles N atom and carbonyl group in HALS-770 interact with the under-coordinated Pb2+, reducing the interface defects. As a result, the unencapsulated device maintains excellent stability over 95 % of its initial efficiency after 30 days in ambient condition with about 25–50 % humidity, and possesses remarkable continuous operation stability with projected T80 > 1400 h at maximum power point tracking in glove box, much higher than those of the pristine device. Meanwhile, HALS-770 enable the PCE of 21.88 % for PSC (0.06 cm2), which is among the highest efficiencies for MAPbI3 based PSCs with p-i-n structure, and the PCE of 19.07 % for PSM (4 cm2). And it is also suitable for FAMA-based devices with n-i-p structure, enabling an efficiency of 23.03 % (0.06 cm2) and excellent stability.

Over 12% efficient CsSnI3 perovskite solar cells enabled by surface post-treatment with bi-functional polar molecules

Eco-friendly all-inorganic tin halide perovskite compounds have drawn significant attention for photovoltaic applications. Nevertheless, the non-radiative recombination derived from the uncoordinated Sn2+ cations at surface and the electron extraction barrier between different functional layers significantly impair the performance of perovskite device. Here we for the first time show that thiophene derivative, 3-thiophenemethylammonium iodide, as an interface modifier between the CsSnI3 perovskite surface and electron transport layer, can passivate defects and reduce the electron extraction potential barrier. The molecules of 3-thiophenemethylammonium iodide can autonomously inter-connect with uncoordinated Sn2+via lone electron pairs of the donated π electrons in electronic-rich thiophene molecule. Moreover, such interface modifier lowers the electron extraction potential barrier at the perovskite/electron transport layer junction in which an interface dipole electric field form. Consequently, the optimized planar solar cell with a structure of ITO/PEDOT:PSS/CsSnI3/ICBA/BCP/Ag, exhibited a power conversion efficiency of 12.05 % under AM 1.5G illumination condition. To the best of our knowledge, this is the highest efficiency for fully inorganic CsSnI3-based devices reported so far. This study represents an innovative approach to realize high-efficiency all-inorganic CsSnI3 perovskite solar cells.

Surface modification of halide perovskite using EDTA-complexed SnO2 as electron transport layer in high performance solar cells.

The long-term performance of metal halide perovskite solar cells (PSCs) can be significantly improved by tuning the surface characteristics of the perovskite layers. Herein, low-temperature-processed ethylenediaminetetraacetic acid (EDTA)-complexed SnO2 (E-SnO2) is successfully employed as an electron transport layer (ETL) in PSCs, enhancing the efficiency and stability of the devices. The effects of EDTA treatment on SnO2 are investigated for different concentrations: comparing the solar cells' response with 15%-2.5% SnO2 and E-SnO2 based ETLs, and it was found that 7.5% E-SnO2 provided the best results. The improved surface properties of the perovskite layer on E-SnO2 are attributed to the presence of small amount of PbI2 which contributes to passivate the defects at the grain boundaries and films' surface. However, for the excess PbI2 based devices, photocurrent dropped, which could be attributed to the generation of shallow traps due to excess PbI2. The better alignment between the Fermi level of E-SnO2 and the conduction band of perovskite is another favorable aspect that enables increased open-circuit potential (VOC), from 0.82 V to 1.015 V, yielding a stabilized power conversion efficiency of 15.51%. This complex ETL strategy presented here demonstrates the enormous potential of E-SnO2 as selective contact to enhance the perovskite layer properties and thereby allow stable and high-efficiency PSCs.

Cascade Reaction in Organic Hole Transport Layer Enables Efficient Perovskite Solar Cells.

The doped organic hole transport layer (HTL) is crucial for achieving high-efficiency perovskite solar cells (PSCs). However, the traditional doping strategy undergoes a time-consuming and environment-dependent oxidation process, which hinders the technology upgrades and commercialization of PSCs. Here, we reported a new strategy by introducing a cascade reaction in traditional doped Spiro-OMeTAD, which can simultaneously achieve rapid oxidation and overcome the erosion of perovskite by 4-tert-butylpyridine (tBP) in organic HTL. The ideal dopant iodobenzene diacetate was utilized as the initiator that can react with Spiro to generate Spiro⋅+ radicals quickly and efficiently without the participation of ambient air, with the byproduct of iodobenzene (DB). Then, the DB can coordinate with tBP through a halogen bond to form a tBP-DB complex, minimizing the sustained erosion from tBP to perovskite. Based on the above cascade reaction, the resulting Spiro-based PSCs have a champion PCE of 25.76 % (certificated of 25.38 %). This new oxidation process of HTL is less environment-dependent and produces PSCs with higher reproducibility. Moreover, the PTAA-based PSCs obtain a PCE of 23.76 %, demonstrating the excellent applicability of this doping strategy on organic HTL.

Broadband enhancement of SiO2@TiO2 light-trapping nanostructure for improving the efficiency of perovskite solar cells

High-efficiency perovskite solar cells (PSCs) are one of the promising candidates to solve the energy crisis worldwide. Optical loss is one of the factors limiting the efficiency of PSCs and antireflection layers provide a dependable method for improving the efficiency of PSCs. Here, a design and optimization of PSCs with a SiO2@TiO2 nanoparticles (NPs) antireflection layer is systematically studied by COMSOL Multiphysics. The effect of different shell-thickness ratios (STRs) on the average light absorption and short-circuit current density of PSCs is simulated and compared with that of planar PSCs. The results show that the average light absorption of PSCs with SiO2@TiO2 NPs of 0.08 STR is 83.21%, which is 5.17% higher than that of PSCs with SiO2 NPs and 10.11% higher than that of planar PSCs. Our results provide theoretical guidance for using SiO2@TiO2 NPs as antireflection layers in the fabrication of PSCs.

Anti-Solvent-Free Fabrication of Stable FA0.9Cs0.1PbI3 Perovskite Solar Cells with Efficiency Exceeding 24.0% through a Naphthalene-Based Passivator.

The anti-solvent-free fabrication of high-efficiency perovskite solar cells (PSCs) holds immense significance for the transition from laboratory-scale to large-scale commercial applications. However, the device performance is severely hindered by the increased occurrence of surface defects resulting from the lack of control over nucleation and crystallization of perovskite using anti-solvent methods. In this study, 2-(naphthalen-2-yl)ethylamine hydriodide (NEAI) is employed as the surface passivator for perovskite films without using any anti-solvent. Naphthalene demonstrates strong π-π conjugation, which aids in the efficient extraction of charge carriers. Additionally, the naphthalene-ring moieties form a tight attachment to the perovskite surface. After NEAI treatment, FA and I vacancies are selectively occupied by NEA+ and I- in NEAI respectively, thus effectively passivating the surface defects and isolating the surface from moisture. Ultimately, the optimized NEAI-treated device achieves a promising power conversion efficiency (PCE) of 24.19% (with a certified efficiency of 23.94%), featuring a high fill factor of 83.53%. It stands out as one of the reported high PCEs achieved for PSCs using the spin-coating technique without the need for any anti-solvent so far. Furthermore, the NEAI-treated device can maintain ≈87% of its initial PCE after 2000h in ambient air with a relative humidity of 30%±5%.

In Situ Synthesized Low-Dimensional Perovskite for >25% Efficiency Stable MA-Free Perovskite Solar Cells.

Developing an additive to effectively regulate the perovskite crystallization kinetics for the optimized optoelectronic properties of perovskite film plays a vital role in obtaining high efficiency and stable perovskite solar cells (PSCs). Herein, a new additive is designed and directly synthesized in perovskite precursor solution by utilizing an addition reaction between but-3-yn-1-amine hydrochloride (BAH) and formamidinium iodide. It is found that its product may control the intermediate precursor phase for regulating perovskite nucleation, leading to advantageous 2D perovskite to induce growth of perovskite along the preferred [001] orientation with not only released lattice strain but also strong interaction with perovskite to passivate its surface defects. By taking advantage of the above synergistic effects, the optimized PSC delivers an efficiency of 25.19% and a high open-circuit voltage (VOC) of 1.22 V. Additionally, the devices demonstrate good stability, remaining over 90% of their initial efficiencies under ambient atmosphere conditions for 60 days, high temperature of 85°C for 200 h, or maximum power point tracking for 500 h.

Regulation of the quantum barrier and carrier transport toward high-efficiency quasi-2D Dion-Jacobson tin perovskite solar cells

Quasi-2D Dion-Jacobson (DJ) tin halide perovskite has attracted much attention due to its elimination of Van der Waals gap and enhanced environmental stability. However, the bulky organic spacers usually form a natural quantum well structure, which brings a large quantum barrier and poor film quality, further limiting the carrier transport and device performance. Here, we designed three organic spacers with different chain lengths (ethylenediamine (EDA), 1,3-propanediamine (PDA), and 1,4-butanediamine (BDA)) to investigate the quantum barrier dependence. Theoretical and experimental characterizations indicate that EDA with short chain can reduce the lattice distortion and dielectric confinement effect, which is beneficial to the effective dissociation of excitons and the inhibition of trap-free non-radiative relaxation. In addition, EDA cation shows strong interaction with the inorganic octahedron, realizing large aggregates in precursor solution and high-quality films with improved structural stability. Furthermore, femtosecond transient absorption proves that EDA cations can also weaken the formation of small n-phases with large quantum barrier to achieve effective carrier transport between different n-phases. Finally, the quasi-2D DJ (EDA)FA9Sn10I31 solar cells achieves a 7.07% power conversion efficiency with good environment stability. Therefore, this work sheds light on the regulation of the quantum barrier and carrier transport through the chain length of organic spacer for quasi-2D DJ lead-free perovskites.

Minimizing Voltage Losses via Synergistically Reducing Hetero-Interface Energy Offset for High Efficiency Perovskite Solar Cells.

The open circuit voltage (VOC) losses at multiple interfaces within perovskite solar cells (PSCs) limit the improvements in power conversion efficiency (PCE). Herein, a tailored strategy is proposed to reduce the energy offset at both hetero-interfaces within PSCs to decrease the VOC losses. For the interface of perovskite and electron transport layer where exists a mass of defects, it uses the pyromellitic acid to serve as a molecular bridge, which reduces non-radiative recombination and energy level offset. For the interface of perovskite and hole transport layer, which includes a passivator of PEAI, the detrimental effect (negative shift of work function) of PEAI passivation and optimizing the interface energy level alignment are neutralized by incorporating (2-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-cyanovinyl)phosphonic acid. Owing to synergistically reduced hetero-interface energy offset, the PSCs achieve a PCE of 25.13%, and the VOC is increased from 1.134 to 1.174V. In addition, the resulting PSCs possess enhanced stability, the unencapsulated PSCs can maintain ≈96% and ≈97% of their initial PCE after 2000h of aging under ambient conditions and 210h under operation conditions.

Enhanced anchoring enables highly efficient and stable inverted perovskite solar cells

The immobilization of all-type ions is critical for further enhancing the efficiency and stability of inverted perovskite solar cells as the volatilization of organic cations and migration of halides could cause device degradation and non-radiative recombination. This work reports a novel and effective multidentate molecular “lock”, 2,3,4,5,6-Pentafluorophenylammonium Iodide (F5PhAI), to simultaneously immobilize all types of ions in perovskite with multiple chemical anchoring sites, leading to enhanced stability of perovskite under thermal and ambient conditions, as well as reduced defect density and energy disorder of perovskite films to significantly inhibit the non-radiative recombination. As a result, F5PhAI-modified device achieves an improved PCE of 24.03%, with a VOC of 1.124 V, a JSC of 25.14 mA cm−2, and an FF of 85.03%. Furthermore, the unencapsulated devices exhibit enhanced long-term stability, maintaining 85% and 90% of the initial efficiencies under 85°C thermal annealing in nitrogen for 500 hours and in humid air condition (RH: 60±10%) for 1000 hours, respectively. This work provides a novel and effective multidentate molecular “lock” strategy to achieve high-efficiency and stable inverted perovskite solar cells.

Recent Progress in Regulating Surface Potential for High-Efficiency Perovskite Solar Cells

Recent Progress in Regulating Surface Potential for High-Efficiency Perovskite Solar Cells

Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation.

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc ) of PSCs from 1.08V to 1.17V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280h testing without pre-processing.

Ammonium iodide-incorporated SnO2 obtains perovskite solar cells with over 24% efficiency

Tin dioxide (SnO2) as the most promising electron transport layer (ETL) has been widely used in high-efficiency perovskite solar cells (PSCs) due to its excellent optical/electronic properties, chemical stability, and low-temperature processing. However, the surface of SnO2 ETL contains defect sites, which result in energy losses in PSCs. In order to passivate the defects of SnO2 surface and together tune the electronic properties of SnO2 ETL for getting high-performance PSCs, we herein incorporate the low-cost material ammonium iodide (NH4I) into the SnO2. After the NH4I doping, the optimized photovoltaic power conversation efficiency is significantly enhanced (the highest efficiency can reach 24.4%), the hysteresis of device is largely suppressed to a negligible level, and the stability of device is also obviously improved. The origin of these enhancements is further disclosed by the positive effects of NH4I doping on both ETL and perovskite film: the surface morphology of ETL is effectively flatten, the energy level of ETL is suitably adjusted, the electron mobility of ETL and the perovskite grain size are clearly increased, the surface defects of ETL and the trap states in the perovskite film are greatly reduced, and the PbI2 residue in the perovskite layer is obviously diminished. The study here of incorporating cheap inorganic small molecule in the ETL provides an ingenious way to enhance the performance of the planar PSCs.

Electron injection and defect passivation for high-efficiency mesoporous perovskite solar cells.

Printable mesoscopic perovskite solar cells (p-MPSCs) do not require the added hole-transport layer needed in traditional p-n junctions but have also exhibited lower power conversion efficiencies of about 19%. We performed device simulation and carrier dynamics analysis to design a p-MPSC with mesoporous layers of semiconducting titanium dioxide, insulating zirconium dioxide, and conducting carbon infiltrated with perovskite that enabled three-dimensional injection of photoexcited electrons into titanium dioxide for collection at a transparent conductor layer. Holes underwent long-distance diffusion toward the carbon back electrode, and this carrier separation reduced recombination at the back contact. Nonradiative recombination at the bulk titanium dioxide/perovskite interface was reduced by ammonium phosphate modification. The resulting p-MPSCs achieved a power conversion efficiency of 22.2% and maintained 97% of their initial efficiency after 750 hours of maximum power point tracking at 55 ± 5°C.

Tailoring the Buried Interface by Dipolar Halogen-Substituted Arylamine for Efficient and Stable Perovskite Solar Cells.

Improving the quality of the buried interface is decisive for achieving stable and high-efficiency perovskite solar cells. Herein, we report the interface engineering by using dipolar 2,4-difluoro-3,5-dichloroaniline (DDE) as the adhesive between titanium dioxide (TiO2) and MAPbI3. By manipulation of the anchoring groups of DDE, this molecule not only passivated defects of TiO2 but also optimized the energy level alignment. Furthermore, the perovskite film on the modified TiO2 surface showed improved crystallinity, released residual stress, and reduced trap states. Therefore, these benefits directly contribute to achieving a power conversion efficiency of up to 22.10%. The unencapsulated device retained 90% of initial power conversion efficiencies (PCE) after continuous light illumination for 1000 h and 93% of initial PCE after exposure to air with a relative humidity of 30-40% for over 3000 h. Moreover, the performance of PSCs based on FA0.15MA0.85PbI3 has also increased from 20.48 to 23.51%. Our results demonstrate the effectiveness and universality of dipolar halogen-substituted arylamine (DDE) for enhancing PSC performance.

Fine optimized cation immobilization strategy for enhancing stability and efficiency of perovskite solar cells

The migration and volatilization of cations within organic–inorganic hybrid perovskite (OIPs) materials has been identified as a major issue for irreversibly degrading perovskite solar cells (PSCs), severely limiting their performance and impeding progress toward large-scale applications. To mitigate these problems, an adjustable cation immobilization strategy was proposed for the first time, in which a series of fluorobenzenesulfonamide (FBSA) molecules was introduced into perovskite precursor, a strong coordination bond was formed between the sulfonamide group with the octahedral imperfection caused by iodine vacancy, along with a hydrogen bond formed between the cation and F atom. As a result, the A-site cations were tightly immobilized in the octahedral of perovskite crystal lattice and the uncoordinated Pb2+ defects were effectively eliminated. Besides, the immobilization distance of cation was finely optimized by changing the substitution position of F atoms. Based on the cation-immobilized perovskite film, the efficiency of PSCs was significantly increased from 19.88 % to 22.30 %. Moreover, the unencapsulated PSCs exhibited impressive light and thermal stability, retaining 82 % of the initial efficiency after 720 h illumination at 1-sun, and maintaining nearly 80 % of the initial PCE after heating at 85 °C for 240 h. Thus, the present study offers a promising approach for advancing the commercialization of stable and high-efficiency perovskite solar cells.