Modification of Energy Level Alignment for Boosting Carbon-Based CsPbI2Br Solar Cells with 14% Certified Efficiency

Hole transfer material (HTM)-free, carbon-based all-inorganic perovskite solar cells (C-PSCs) are promising alternatives to conventional organic–inorganic hybrid PSCs in addressing thermal and moisture instability issues. However, the energy level mismatch between the inorganic perovskite and carbon electrode coupled, together with the incapability of the carbon electrode to reflect incident light for reabsorption, limits the power conversion efficiency (PCE) of C-PSCs. To address these issues, herein, a new strategy of a hexyltrimethylammonium bromide (HTAB)-modified CsPbI₂Br perovskite surface is devised to reduce this energy offset from 0.70 to 0.32 eV and increase the built-in potential by 70 mV for the final devices. Additionally, a CsPbI₂Br perovskite film with a thickness of up to 800 nm is realized via a hot-flow-assisted spin coating approach in an ambient atmosphere with humidity of less than 80%. Reduced energy offset coupled with suppressed charge recombination and thick perovskite layer boosts the champion PCE of CsPbI₂Br C-PSCs to 14.3% (J_sc = 14.1 mA cm⁻², V_oc = 1.26 V, and fill factor = 0.806), and the average PCE to 13.9% under one sun illumination. A new certified efficiency record of 14.0% is obtained for HTM-free inorganic C-PSCs. Meanwhile, the moisture-resistant barrier from the alkyl chain in HTAB improves the stability of the final devices.     

Chromium-Based Metal–Organic Framework as A-Site Cation in CsPbI2Br Perovskite Solar Cells

Inorganic CsPbI_xBr_3−x perovskite solar cells (PSCs) have gained enormous interest due to their excellent thermal stabilities. However, their intrinsically poor moisture stability hampers their further development. Herein, a chromium-based metal–organic framework group is intercalated inside the inorganic Pb I framework, resulting in a new multiple-dimensional electronically coupled CsPbI₂Br perovskite. In this structurally and electronically coupled perovskite, the π-conjugated terpyridyl can delocalize the excited valence electrons of metal Cr³⁺ ion, enabling multi-interactive charge-carrier transport channels within CsPbI₂Br perovskites. The stability and efficiency of the produced devices are substantially enhanced in comparison to their counterparts with only a pristine CsPbI₂Br active layer. The optimized all-inorganic PSC yields a power conversion efficiency (PCE) as high as 17.02%. Remarkably, the stabilized device retains 80% of its PCE after 1000 h in the ambient atmosphere. This study provides a new paradigm toward addressing the stability challenge of the inorganic perovskite while enhancing its carrier transport ability.     

In-Situ Hot Oxygen Cleansing and Passivation for All-Inorganic Perovskite Solar Cells Deposited in Ambient to Breakthrough 19% Efficiency

All-inorganic perovskite CsPbI₃ has attracted extensive attention recently because of its excellent thermal and chemical stability. However, its photovoltaic performance is hindered by large energy losses (E_loss) due to the presence of point defects. In addition, hydroiodic acid (HI) is currently employed as a hydrolysis-derived precursor of intermediate compounds, which often leads to a small amount of organic residue, thus undermining its chemical stability. Herein, an in-situ hot oxygen cleansing with superior passivation (HOCP) for the triple halide-mixed CsPb(I_2.85Br_0.149Cl_0.001) perovskite solar cells (abbreviated as CsPbTh₃) deposited in an ambient atmosphere to reduce the E_loss to as low as 0.48 eV for the power conversion efficiency (PCE) to reach 19.65% is demonstrated. It is found that the hot oxygen treatment effectively removes the organic residues. Meanwhile, it passivates halide vacancies, hence reduces the trap states and nonradiative recombination losses within the perovskite layer. As a result, the PCE is increased significantly from 17.15% to 19.65% under 1 sun illumination with an open-circuit voltage enlarged to 1.23 from 1.14 V, which corresponds to an E_loss reduction from 0.57 to 0.48 eV. Also, the HOCP-treated devices exhibit better long-term stability. This insight should pave a way for decreasing nonradiative charge recombination losses for high-performance inorganic perovskite photoelectronics.     

Molecularly Tailored Surface Defect Modifier for Efficient and Stable Perovskite Solar Cells

Surface defects cause non-radiative charge recombination and reduce the photovoltaic performance of perovskite solar cells (PSCs), thus effective passivation of defects has become a crucial method for achieving efficient and stable devices. Organic ammonium halides have been widely used for perovskite surface passivation, due to their simple preparation, lattice matching with perovskite, and high defects passivation ability. Herein, a surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is employed as the interfacial layer between the spiro-OMeTAD and perovskite layer to modify the surface defect states. It is found that TMBAI treatment suppresses the nonradiative charge carrier recombination, resulting in a 60 mV increase of the open-circuit voltage (V_oc) (from 1.11 to 1.17 V) and raises the fill factor from 76.3% to 80.3%. As a result, the TMBAI-based PSCs device demonstrates a power conversion efficiency (PCE) of 23.7%. Remarkably, PSCs with an aperture area of 1 square centimeter produce a PCE of 21.7% under standard AM1.5 G sunlight. The unencapsulated TMBAI-modified device retains 92.6% and 90.1% of the initial values after 1000 and 550 h under ambient conditions (humidity 55%–65%) and one-sun continuous illumination, respectively.     

One-Source Strategy Boosting Dopant-Free Hole Transporting Layers for Highly Efficient and Stable CsPbI2Br Perovskite Solar Cells

All-inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their organic–inorganic hybrid counterparts. However, the inferior film quality and doped hole transport layer (HTL) have a strong tendency to degrade the perovskite under high temperatures or harsh operating conditions. To solve these problems, a one-source strategy using the same polymer donor material (PDM) to simultaneously dope CsPbI₂Br perovskite films via antisolvent engineering and fabricating the HTL is proposed. The doping assists perovskite film growth and forms a top–down gradient distribution, generating CsPbI₂Br with enlarged grain size and reduced defect density. The PDM as the HTL suppresses the energy barrier and forms favorable electrical contacts for hole extraction, and assemble into a fingerprint-like morphology that improves the conductivity, facilitating the creation of a dopant-free HTL. Based on this one-source strategy using PBDB-T as PDM, the CsPbI₂Br perovskite solar cell with a dopant-free HTL achieves a power conversion efficiency (PCE) of 16.40%, which is one of the highest PCEs reported among all-inorganic CsPbI₂Br pero-SCs with a dopant-free HTL. Importantly, the devices exhibit the highest thermal stability at 85 °C and operational stability under continuous illumination even with Ag as the top electrode and present good universality.     

Efficient Passivation Strategy on Sn Related Defects for High Performance All-Inorganic CsSnI3 Perovskite Solar Cells

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)-based PSCs outperform the reported Pb-free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high-performance all-inorganic CsSnI₃ PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI₃ perovskites is reported. The thiosemicarbazide (TSC) with SC N functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn²⁺ ion and Sn²⁺ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI₃ PSCs. The surface passivated all-inorganic CsSnI₃ PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all-inorganic lead-free Sn-based PSCs.     

Constructing All-Inorganic Perovskite/Fluoride Nanocomposites for Efficient and Ultra-Stable Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have rapidly developed over the past decade and have achieved the latest certified power conversion efficiency (PCE) up to 25.5%. However, unsatisfactory long-term operational stability for these hybrid PSCs remains a huge obstacle to further development and commercialization. Herein, a unique hetero-structured CsPbI₃/CaF₂ perovskite/fluoride nanocomposites (PFNCs) is fabricated via a newly developed facile two-step hetero-epitaxial growth strategy to deliver efficient and ultra-stable PSCs. After being incorporated into the crystal lattice of α-phase CsPbI₃ perovskite, the cubic-phase CaF₂ in the resultant CsPbI₃/CaF₂ PFNCs can not only passivate the intrinsic defects of CsPbI₃ perovskite itself but also effectively suppress the notorious ion migration in hybrid perovskite Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45 (CsFAMA) thin-films of PSCs. As such, the CsFAMA PSC devices based on CsPbI₃/CaF₂-deposited perovskite thin-film achieve a mean PCE of 20.45%, in sharp contrast to 19.33% of the control devices without deposition. Specifically, the CsPbI₃/CaF₂-deposited PSC retains 85% of its original PCE after 1000 h continuous operation at the maximum power point under AM 1.5G solar light, far better than those of the control and CsPbI₃-deposited PSCs with a device T₈₅ lifetime of 315 and 125 h, respectively.     

Inorganic Ammonium Halide Additive Strategy for Highly Efficient and Stable CsPbI3 Perovskite Solar Cells

All-inorganic perovskite cesium lead iodide (CsPbI₃) exhibits excellent prospects for commercial application as a light absorber in single-junction or tandem solar cells due to its outstanding thermal stability and proper bandgap. However, the device performance of CsPbI₃-based perovskite solar cells (PSCs) is still restricted by the unsatisfactory crystal quality and severe non-radiative recombination. Herein, inorganic additive ammonium halides are introduced into the precursor solution to regulate the nucleation and crystallization of the CsPbI₃ film by exploiting the atomic interaction between the ammonium group and the Pb–I framework. The grain boundaries and interfacial contact of the CsPbI₃ film have been improved, which leads to significant suppression in the non-radiative recombination and an enhancement in the charge transport ability. With these benefits, a high efficiency of 18.7% together with an extraordinarily high fill factor of 0.83–0.84 has been achieved, comparable to the highest records reported so far. Moreover, the cell exhibits ultra-high photoelectrical stability under continuous light illumination and high bias voltage with 96% of its initial power-conversion efficiency being sustained after 2000 h operation, even superior to the world-champion CsPbI₃ solar cell. The findings are promising for the development and application of all-inorganic PSCs using a simple inorganic additive strategy.     

Dual-Phase Stabilized Perovskite Nanowires for Reduced Defects and Longer Carrier Lifetime

1D perovskite materials are of significant interest to build a new class of nanostructures for electronic and optoelectronic applications. However, the study of colloidal perovskite nanowires (PNWs) lags far behind those of other established perovskite materials such as perovskite quantum dots and perovskite thin films. Herein, a dual-phase passivation strategy to synthesize all-inorganic PNWs with minimized surface defects is reported. The local phase transition from CsPbBr₃ to CsPb₂Br₅ in PNWs increases the photoluminescence quantum yield, carrier lifetime, and water-resistivity, owing to the energetic and chemical passivation effect. In addition, these dual-phase PNWs are employed as an interfacial layer in perovskite solar cells (PSCs). The enhanced surface passivation results in an efficient carrier transfer in PSCs, which is a critical enabler to increase the power conversion efficiency (PCE) to 22.87%, while the device without PNWs exhibits a PCE of 20.74%. The proposed strategy provides a surface passivation platform in 1D perovskites, which can lead to the development of novel nanostructures for future optoelectronic devices.     

Surface Regulation through Dipolar Molecule Boosting the Efficiency of Mixed 2D/3D Perovskite Solar Cell to 24%

Mixed 2D/3D perovskite solar cells (PSCs) show promising performances in efficiency and long-term stability. The functional groups terminated on a large organic molecule used to construct 2D capping layer play a key role in the chemical interaction mechanism and thus influence the device performance. In this study, 4-(trifluoromethyl) benzamidine hydrochloride (TFPhFACl) is adopted to construct 2D capping layer atop 3D perovskite. It is found that there are two mechanisms synergistically contributing to the increase of efficiency: 1) The TFPhFA⁺ cations form a dipole layer promoting the interfacial charge transport. 2) The suppressed nonradiative recombination of perovskite through the coordination of TFPhFA⁺ cations with Pb–I octahedron, as well as the recrystallization of 3D perovskite induced by Cl^- ions. As a result, the PSC delivers an efficiency of 24.0% with improved open-circuit voltage (V_OC) of 1.16 V, short-circuit current density (J_SC) of 25.42 mA cm^-2, and fill factor of 81.26%. The device shows no decrease in efficiency after 1500 h stored in the air indicating the good stability. The utilization of TFPhFACl not only provides a facile way to optimize the interfacial problems, but also gives a new perspective for rational design of large spacer molecule for constructing efficient 2D/3D PSCs.     

3D Polydentate Complexing Agents for Passivating Defects and Modulating Crystallinity for High-Performance Perovskite Solar Cells

The grain boundaries (GBs)/surface defects within perovskite film directly impede the further improvement of photoelectric conversion efficiency (PCE) and stability of planar perovskite solar cells (PSCs). Herein, 3D phytic acid (PA) and phytic acid dipotassium (PAD) with polydentate are explored to synchronously passivate the defects of perovskite absorber directly in multiple spatial directions. The strong electron-donating groups ( H₂PO₄) in the PA molecule afford six anchor sites to bind firmly with uncoordinated Pb²⁺ at the GBs/surface and modulate perovskite crystallization, thus enhancing the quality of perovskite film. Particularly, PAD containing an additional (K→PO) push–pull structure promotes the dominant coordination of phosphate group (PO) with Pb²⁺ and passivates halide anion defects due to the complexation of potassium ions (K⁺) with iodide ions (I^-). Consequently, the PAD-complexed PSCs deliver a champion PCE of 23.18%, which is remarkably higher than that of the control device (19.94%). Meanwhile, PAD-complexed PSCs exhibit superior moisture and thermal stability, remaining 79% of their initial PCE after 1000 h under continuous illumination, while the control device remain only 48% of their PCE after 1000 h. This work provides important insights into designing multifunctional 3D passivators for the purpose of simultaneously enhancing the efficiency and stability of devices.     

Multifunctional Aminoglycoside Antibiotics Modified SnO2 Enabling High Efficiency and Mechanical Stability Perovskite Solar Cells

SnO₂ as an electron transport layer (ETL) has been widely used in regular planar perovskite solar cells (PSCs) owing to its high optical transmittance, less photocatalytic activity, and low-temperature processing. However, SnO₂-based PSCs still face many challenges which greatly impair their efficiency and stability of PSCs. Herein, a novel and effective multifunctional modification strategy is proposed by incorporating streptomycin sulfate (STRS) molecules with multiple functional groups into SnO₂ ETL. STRS can significantly suppress SnO₂ nanoparticle agglomeration, improve the electronic property of SnO₂, as well as reduce nonradiative recombination. At the same time, interfacial residual tensile stress is released and the interfacial energy level alignment becomes more matched. As a result, the STRS-modified PSCs achieve a higher efficiency of 22.89% compared to 20.61% of the control device and exhibit a hysteresis-free feature. The humidity and thermal stability of PSCs based on STRS-SnO₂ are significantly improved. Furthermore, the efficiency of flexible devices increased from 19.74% to 20.79%, and the devices still maintain >80% of initial PCE after 4500 bending cycles with a bend radius of 5 mm. This study provides a low-cost, facile, and efficient strategy for achieving high efficiency and stability in PSCs.     

Illumination Enhanced Crystallization and Defect Passivation for High Performance CsPbI3 Perovskite Solar Cells by Sacrificing Dye

All-inorganic perovskite solar cells (PSCs) have been the research focus due to their high thermal stability and proper band gap for tandem solar cells. However, their power conversion efficiency (PCE) is still lower than that of organic-inorganic hybrid PSCs. Herein, a sacrificing dye (Rhodamine B isothiocyanate, RBITC) is developed to regulate the growth of perovskite film by in situ release of ethylammonium cations, isothiocyanate anions and benzoic acid molecules upon annealing and illumination. The ethylammonium cations can efficiently passivate surface defects. The isothiocyanate anions incorporate with uncoordinated Pb to regulate the crystallization process. The benzoic acid molecules facilitate the nucleation of the perovskite crystals. Especially, the illumination can accelerate the release of these beneficial ions/molecules to improve the quality of perovskite films further. After optimization with RBITC, a high open circuit voltage (V_OC) of 1.24 V and a champion PCE of 20.95% are obtained, which are among the highest Voc and PCE values of CsPbI₃ PSCs. Accordingly, the operational stability of the PSC devices is significantly improved. The results provide an efficient chemical strategy to regulate the formation of perovskite films in whole crystallization process for high performance all-inorganic PSCs.     

Multifunctional Small Molecule as Buried Interface Passivator for Efficient Planar Perovskite Solar Cells

The improvement of power conversion efficiency (PCE) and stability of the perovskite solar cell (PSC) is hindered by carrier recombination originating from the defects at the buried interface of the PSC. It is crucial to suppress the nonradiative recombination and facilitate carrier transfer in PSC via interface engineering. Herein, P-biguanylbenzoic acid hydrochloride (PBGH) is developed to modify the tin oxide (SnO₂)/perovskite interface. The effects of PBGH on carrier transportation, perovskite growth, defect passivation, and PSC performance are systematically investigated. On the one hand, the PBGH can effectively passivate the trap states of Sn dangling bonds and O vacancies on the SnO₂ surface via Lewis acid/base coordination, which is conducive to improving the conductivity of SnO₂ film and accelerating the electron extraction. On the other hand, PBGH modification assists the formation of high-quality perovskite film with low defect density due to its strong interaction with PbI₂. Consequently, the PBGH-modified PSC exhibits a champion power conversion efficiency (PCE) of 24.79%, which is one of the highest PCEs among all the FACsPbI₃-based PSCs reported to date. In addition, the stabilities of perovskite films and devices under high temperature/humidity and light illumination conditions are also systematically studied.     

Synergistic Crystallization Modulation and Defects passivation via Additive Engineering Stabilize Perovskite Films for Efficient Solar Cells

Organic-inorganic lead halide perovskite are promising photovoltaic materials, but their intrinsic defects and crystalline quality severely deteriorate the solar cells efficiency and stability. Herein, potassium 1,1,2,2,3,3-hexafluoroprop-ane-1,3-disulfonimide (KHFDF) is introduced into PbI₂ precursor solution to passivate various defects and improve the crystalline quality of perovskite films. It is found that KHFDF can inhibit PbI₂ crystallization, thus tuning the crystal orientation and growth of perovskite films. Furthermore, KHFDF with dual-functional sulfonyl group cannot only passivate grain boundaries (GBs), but also passivate the defects at GBs via strong interaction with undercoordinated Pb²⁺ and/or hydrogen bonding with FA⁺, while the K⁺ counter cations allow ionic interaction with undercoordinated I⁻. As a result, the KHFDF-modified films exhibit high quality with a larger grain size and a reduced trap-state density, thereby suppressing the trap-state nonradiative recombination. And the devices show a champion efficiency up to 24.15%, benefiting from a sharp enhancement of open-circuit voltage (V_oc) of 1.183 V and fill factor of 81.78%. In addition, due to the enhanced humidity tolerance and chemical structure stability, the devices exhibit excellent long-term humidity and thermal stability without encapsulation.     

Low-Temperature Crystallized and Flexible 1D/3D Perovskite Heterostructure with Robust Flexibility and High EQE-Bandwidth Product

All-inorganic perovskite cesium lead triiodide (CsPbI₃) has attracted much attention among the perovskite family due to its excellent optoelectronic properties and chemical stability. However, the high-temperature crystallization process makes CsPbI₃ less compatible with commercially flexible substrates, limiting its application into flexible optoelectronics. Here, a cation of 1-(3-aminopropyl)-2pyrrolidinone (APP) is reported that can form 1D (APP)PbI₃ perovskite as templates, and significantly reduce the CsPbI₃ black-phase transition energy with a low annealing temperature of 75 °C, which further enables a flexible (APP)PbI₃/γ-CsPbI₃ (1D/3D) heterostructure photodetector on ITO/PET substrate. A high external quantum efficiency (EQE) greater than 2377% is observed along the orientated 1D/3D heterostructure. The high gain and low noise result in a high specific detectivity (D*) over 10¹² Jones under −0.6 V low bias. The optimized device structure brings a high EQE × bandwidth product of 119 kHz under a low driving bias. Due to the high toughness of orientated APP⁺ ions and the face-connected [PbI₃]⁻ chains structure as a strong energy absorber, the flexible photodetector also shows excellent phase stability and impressive flexibility, remaining >90% initial responsivity after over 20 000 times bending with potential flexible imaging application in harsh environments.     

Highly-Stable CsPbI3 Perovskite Solar Cells with an Efficiency of 21.11% via Fluorinated 4-Amino-Benzoate Cesium Bifacial Passivation

The poor interface quality between cesium lead triiodide (CsPbI₃) perovskite and the electron transport layer limits the stability and efficiency of CsPbI₃ perovskite solar cells (PSCs). Herein, a 4-amino-2,3,5,6-tetrafluorobenzoate cesium (ATFC) is designed as a bifacial defect passivator to tailor the perovskite/TiO₂ interface. The comprehensive experiments demonstrate that ATFC can not only optimize the conductivity, electron mobility, and energy band structure of the TiO₂ layer by passivation of the undercoordinated Ti⁴⁺, oxygen vacancy (V_O), and free  OH defects but also promote the yield of high-quality CsPbI₃ film by synergistic passivation of undercoordinated Pb²⁺ defects with the  CO group and F atom, and limiting I⁻ migration via F···I interaction. Benefiting from the above interactions, the ATFC-modified CsPbI₃ device yields a champion power conversion efficiency (PCE) of 21.11% and an excellent open-circuit voltage (V_OC) of 1.24 V. Meanwhile, the optimized CsPbI₃ PSC maintains 92.74% of its initial efficiency after aging 800 h in air atmosphere, and has almost no efficiency attenuation after tracking at maximum power point for 350 h.     

Anti-Dissociation Passivation via Bidentate Anchoring for Efficient Carbon-Based CsPbI2.6Br0.4 Solar Cells

Molecular passivation on perovskite surface is an effective strategy to inhibit surface defect-assisted recombination and reduce nonradiative recombination loss in perovskite solar cells (PSCs). However, the majority of passivating molecules bind to perovskite surface through weak interactions, resulting in weak passivation effects and susceptible to interference from various factors. Especially in carbon-based perovskite solar cells (C-PSCs), the molecular passivation effect is more susceptible to disturbance in subsequent harsh preparation of carbon electrodes via blade-coating route. Herein, bidentate ligand 2,2′-Bipyridine (2Bipy) is explored to passivate surface defects of CsPbI_2.6Br_0.4 perovskite films. The results indicate that compared with monodentate pyridine (Py), bidentate 2Bipy shows a stronger chelation with uncoordinated Pb(II) defects and exhibits a greater passivation effect on perovskite surface. As a result, 2Bipy-modified perovskite films display a significantly boosted photoluminescence lifetime, accompanied by excellent anchoring stability and anti-dissociation of passivating molecules. Meanwhile, the moisture resistance of the 2Bipy-modified perovskite films is also significantly enhanced. Consequently, the efficiency of C-PSCs is improved to 16.57% (J_sc = 17.16 mA cm⁻², V_oc = 1.198 V, FF = 80.63%). As far as it is known, this value represents a new record efficiency for hole transport material-free inorganic C-PSCs.     

Design and Synthesis of Fluorinated Quantum Dots for Efficient and Stable 0D/3D Perovskite Solar Cells

Dimensionality engineering involving the low-dimensional and 3D perovskites has been demonstrated as an efficient promising strategy to modulate interfacial energy loss as well as instability in perovskite solar cells (PSCs). Herein, the use of fluorinated Cesium Lead Iodide (CsPbI₃) perovskite quantum dot (PQD) is first reported as interface modification layer for PSCs. The binding between the CsPbI₃ PQD surface and native oleic acid (OLA)/oleylamine (OAm) ligands is governed by a dynamic adsorption–desorption equilibrium. Perfluorooctanoic acid (PFA) with stronger binding affinity and more hydrophobic nature is explored to partially replace OLA to prepare the fluorinated ligand capped CsPbI₃ PQDs (F-CsPbI₃). Through optimization of the addition of PFA during hot-injection synthesis, the in situ treated F-CsPbI₃ PQDs display reduced surface defect states, higher photoluminescence quantum yields together with improved stability. Subsequently, both CsPbI₃ and F-CsPbI₃ PQDs are utilized as interface engineering layer in PSCs, delivering the best efficiency values of 21.99% and 23.42%, respectively, which is significantly enhanced compared to the control device (20.37%). More importantly, benefiting from its more hydrophobic properties, the F-CsPbI₃ PQD treated device exhibits excellent ambient storage stability (25 °C, relative humidity: 35–45%), retaining over 80% of its initial efficiency after 1500 h aging.     

Dual Sub-Cells Modification Enables High-Efficiency n–i–p Type Monolithic Perovskite/Organic Tandem Solar Cells

Monolithic perovskite/organic tandem solar cells (POTSCs) have attracted increasing attention owing to ability to overcome the Shockley–Queisser limit. However, compromised sub-cells performance limits the tandem device performance, and the power conversion efficiency (PCE) of POTSCs is still lower than their single-junction counterparts. Therefore, optimized sub-cells with minimal energy loss are desired for producing high-efficiency POTSCs. In this study, an ionic liquid, methylammonium acetate (MAAc), is used to modify wide-bandgap perovskite sub-cells (WPSCs), and bathocuproine (BCP) is used to modify small-bandgap organic solar cells. The Ac⁻ group of MAAc can effectively heal the Pb defects in the all-inorganic perovskite film, which enables a high PCE of 17.16% and an open-circuit voltage (V_oc) of 1.31 V for CsPbI_2.2Br_0.8-based WPSCs. Meanwhile, the BCP film, inserted at the ZnO/organic bulk-heterojunction (BHJ) interface, acts as a space layer to prevent direct contact between ZnO and the BHJ while passivating the surface defects of ZnO, thereby mitigating ZnO defect-induced efficiency loss. As a result, PM6:CH1007-based SOSCs exhibit a PCE of 15.46%. Integrating these modified sub-cells enable the fabrication of monolithic n–i–p structured POTSCs with a maximum PCE of 22.43% (21.42% certified), which is one of the highest efficiencies in such type of POTSCs.