Initial Power Conversion Efficiency Research Articles

Stable Surface Contact with Tailored Alkylamine Pyridine Derivatives for High-Performance Inverted Perovskite Solar Cells.

Formamidinium-cesium lead triiodide (FA1-xCsxPbI3) perovskite holds great promise for perovskite solar cells (PSCs) with both high efficiency and stability. However, the defective perovskite surfaces induced by defects and residual tensile strain largely limit the photovoltaic performance of the corresponding devices. Here, the passivation capability of alkylamine-modified pyridine derivatives for the surface defects of FA1-xCsxPbI3 perovskite is systematically studied. Among the studied surface passivators, 3-(2-aminoethyl)pyridine (3-PyEA) with the suitable size is demonstrated to be the most effective in reducing surface iodine impurities and defects (VI and I2) through its strong coordination with Npyridine. Additionally, the tail amino group (─NH2) from 3-PyEA can react with FA+ cations to reduce the surface roughness of perovskite films, and the reaction products can also passivate FA vacancies (VFA), and further strengthen their binding interaction to perovskite surfaces. These merits lead to suppressed nonradiative recombination loss, the release of residual tensile stress for the perovskite films, and a favorable energy-level alignment at the perovskite/[6,6]-phenyl-C61-butyric acid methyl ester interface. Consequently, the resulting inverted FA1-xCsxPbI3 PSCs obtain an impressive power conversion efficiency (PCE) of 25.65% (certified 25.45%, certified steady-state efficiency 25.06%), along with retaining 96.5% of the initial PCE after 1800 h of 1-sun operation at 55 °C in air.

Interfacial Proton Precompensation: Suppressing Deprotonation-Driven Lattice Collapse for Enhanced Efficiency and Stability in Perovskite Solar Cells.

The chemical property of the buried interface plays a crucial role in improving the performance and stability of perovskite solar cells (PSCs). The SnO2/perovskite interface prepared from SnO2 alkaline hydrogel with high proton affinity triggers directional migration and irreversible reactions of protons, exacerbating the disintegration of perovskite crystal. In this study, we proposed proton precompensation strategy to suppress the deprotonation effect of the buried interface and improve the durability of the devices. By modulating the chemical environment and surface energy state of the buried interface, the domain-limiting and spontaneous compensation of protons in formamidinium (FA+) under Coulomb force were achieved, thereby stabilizing the perovskite crystal structure. The stability of target perovskite films under UV illumination and heating at 85 °C was significantly enhanced. As a result, the devices can retain around 90% of their initial power conversion efficiency (PCE) after 1000 h of continuous irradiation at the maximum power point (MPP). Moreover, due to the reduction of defect content at the buried interface and the improvement of conductivity and carrier mobility by the precompensation treatment, the interfacial energy loss and non-radiative recombination were substantially diminished. The target PSC devices exhibited much higher PCE of 25.55% than the control devices (23.03%).

Interfacial Proton Precompensation: Suppressing Deprotonation‐Driven Lattice Collapse for Enhanced Efficiency and Stability in Perovskite Solar Cells

The chemical property of the buried interface plays a crucial role in improving the performance and stability of perovskite solar cells (PSCs). The SnO2/perovskite interface prepared from SnO2 alkaline hydrogel with high proton affinity triggers directional migration and irreversible reactions of protons, exacerbating the disintegration of perovskite crystal. In this study, we proposed proton precompensation strategy to suppress the deprotonation effect of the buried interface and improve the durability of the devices. By modulating the chemical environment and surface energy state of the buried interface, the domain‐limiting and spontaneous compensation of protons in formamidinium (FA+) under Coulomb force were achieved, thereby stabilizing the perovskite crystal structure. The stability of target perovskite films under UV illumination and heating at 85 °C was significantly enhanced. As a result, the devices can retain around 90% of their initial power conversion efficiency (PCE) after 1000 h of continuous irradiation at the maximum power point (MPP). Moreover, due to the reduction of defect content at the buried interface and the improvement of conductivity and carrier mobility by the precompensation treatment, the interfacial energy loss and non‐radiative recombination were substantially diminished. The target PSC devices exhibited much higher PCE of 25.55% than the control devices (23.03%).

Hexafluoroisopropanol modified MXene for perovskite surface remodeling and interfacial dipole effect enhancement

The development of high-efficiency and stable perovskite (PVK) solar cells (PSCs) still faces the challenge of non-ideal interfaces between PVK and charge transport layers. Herein, the hexafluoroisopropanol (HFIP) modified two-dimensional Ti3C2Tx MXene is custom-made (MX-HFIP) and employed as the interlayer between the PVK and hole transport layer (HTL) interface by forming hydrogen bonds. The MX-HFIP serves to reinforce the interface contact and remodel the surface of PVK, leading to a high-quality PVK film with a significantly reduced defect density, suppressed nonradiative recombination, and inhibited invasion of water and oxygen. Moreover, the synergistic effect of MXene and HFIP results in an enhanced interfacial dipole effect and an optimized energy-level alignment, thereby increasing the driving force for charge extraction and transport at the PVK/HTL interface. Therefore, the MX-HFIP treated PSC achieves a substantially-enhanced power conversion efficiency (PCE) of 22.33 %, as compared to 20.05 % of the untreated device. Besides, the MX-HFIP treated PSC delivers significantly enhanced stabilities, with 88 % of its initial PCE after 1656 h of storage at 25 °C under 30 %⁓40 % relative humidity. These findings demonstrate the advancement using fluorine-rich molecule modified MXene to improve interfacial properties for enhancing performances and stabilities of optoelectronic devices.

Cation reactivity inhibits perovskite degradation in efficient and stable solar modules.

Perovskite solar modules (PSMs) show outstanding power conversion efficiencies (PCEs), but long-term operational stability remains problematic. We show that incorporating N,N-dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]+) cation effectively improved perovskite film. The in situ formation of [MTTZ]+ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. The optimized PSMs achieved a record (certified) PCE of 23.2% with an aperture area of 27.2 cm2, with a stabilized PCE of 23.0%. The encapsulated PSM retained 87.0% of its initial PCE after ~1900 hours of maximum power point tracking at 85°C and 85% relative humidity under 1.0-sun illumination.

Molecular engineering of oxadiazole-based small organic-functional molecules as hole transporting materials for dopant-free perovskite solar cells

The present investigation concerns the synthesis and characterization of new hole-transporting materials (HTMs) for dopant free perovskite solar cells (PSCs). In this work, emphasis is placed on three new HTMs, specifically materials P-H, P-OMe, and P-CN, whose center-core is 2,2'-(4,8-bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene (OBDT) and combined with two donor units of substituted triphenylamine as at both ends along with oxadiazole acceptor units in between donor and OBDT. The fabrication of perovskite solar cell devices using new HTMs and compared the power conversion performance with the standard spiro-OMeTAD HTM. Several spectroscopic techniques were utilized to characterize the properties of the new HTMs, such as FESEM analysis of thin-film morphologies, time-dependent photoluminescence (PL) spectra, and mobility measurements. The HTMs P-OMe established a compressed and steady protective layer on the perovskite layer. This layer contributed to the development of open-circuit voltage (VOC) and short-circuit current density (JSC), both of which are crucial for accomplishing high power conversion efficiency (PCE) in PSCs. The PSC device integrating the P-OMe HTM displayed a superior PCE of 21.14 % over an active area of 0.22 cm2. This activity was related to the standard device that utilized the standard Spiro-OMeTAD HTM, which accomplished a PCE of 17.46 %. The improved devices with the P-OMe HTM continued about 90 % of their initial PCE throughout maximum power point tracking (MPPT) for 90 days. Furthermore, these devices engaged in their activity over a further 2160 h under various temperature settings (25 °C and 35 °C), probably because of the hydrophobic property of the HTM.

Indium oxide buffer layer for perovskite/Si 4-terminal tandem solar cells with efficiency exceeding 30%

Perovskite/Si tandem solar cells (TSCs) present great potential to surpass the Shockley-Queisser limit of single-junction solar cells for further advancing the power conversion efficiency (PCE) of solar cells. However, the fabrication of TSCs usually encounters challenge of selecting suitable sputtering buffer layer (SBL) to prevent the bombardment during the transparent electrode deposition. Herein, we introduce an indium oxide (In2O3) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells (ST-PSCs). The optical transmittance and electrical conductivity of In2O3 highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In2O3 film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering. A 1.68 eV ST-PSC incorporating this In2O3 buffer layer exhibits a champion PCE of 20.20%, demonstrating the excellent optoelectronic and protective properties of In2O3. When combined with a Si subcell, the 4-terminal TSC obtains a remarkable PCE of 30.04%. Importantly, the unencapsulated ST-PSC maintained 80% of initial PCE after 423 h of continuous light soaking in N2. This work has provided a facile and instrumental transparent SBL strategy for perovskite/Si TSCs.

Enhancing Stability in All-Vacuum-Evaporated Hybrid Perovskite Solar Cells via a Bipolar Host as a Hole-Transporting Layer.

Growing an ultrathin hybrid organic-inorganic perovskite film while maintaining high efficiency and addressing photostability challenges for commercial devices remains a significant hurdle. In this study, we explore the incorporation of organometallic copper phthalocyanine (CuPc) and MS-OC (a previously published spiro-based interfacial material for perovskite solar cells (PSCs), featuring an ortho-oriented carbazole donor) as an addition to the hole-transporting layer (HTL) in all-vacuum-deposited Cs0.06FA0.94Pb(I0.68Br0.32)3 PSCs. By innovatively introducing a 3 nm-thin MS-OC layer at the CuPc-perovskite interface, we achieve a deeper understanding of the crystallographic dynamics of perovskites, resulting in a uniform and pinhole-free film. We demonstrate that PSCs utilizing the CuPc HTL with an MS-OC interfacial layer in a p-i-n architecture achieve a power conversion efficiency (PCE) of up to 14.42%. Remarkably, the CuPc/MS-OC-based device exhibits outstanding long-term photostability, maintaining its initial PCE over 400 h (T100 = 400 h) under continuous sunlight illumination. By configuring the device architecture as ITO/MoO3/CuPc/MS-OC/perovskite/C60/BCP/Ag, we find that the evaporated MS-OC thin films effectively reduce nonradiative losses, passivate the perovskite, and enhance device performance. Our findings indicate that the polarity of the underlying surface significantly influences perovskite nucleation, underscoring the potential to improve photostability by controlling interfacial imperfections.

An n-Doping Cross-Linkable Quinoidal Compound as an Electron Transport Material for Fully Stretchable Inverted Organic Solar Cells.

The photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, an intrinsically stretchable ETL for inverted OSCs through a side-chain cross-linking strategy has been developed. Specifically, cross-linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr-PEI-50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack-onset strain>45 %). When used as the ETL in inverted OSCs, QBr-PEI-50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27 % and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr-PEI-50 in fully stretchable inverted OSCs yielded a PCE of 14.01 %, and 80 % of the initial PCE was maintained after 21 % strain, showcasing its potential for wearable electronics.

Small Molecular Dibenzo[b,d]thiophene-Based Hole Transport Materials for Tin-Lead Perovskite Solar Cell.

The most commonly used hole transport material (HTM) in tin-lead (Sn-Pb) perovskite solar cells (PSCs) is the aqueous poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), and its inherent hygroscopic and acidic features greatly limit the power conversion efficiency (PCE) and stability of PSCs. Concerning this, by selecting dibenzo[b,d]thiophene 5,5-dioxide (DBTDO) as the core and engineering the donor units, 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline (TPA) and N1-(4-(bis(4-methoxyphenyl)amino)phenyl)-N4,N4-bis(4-methoxyphenyl)benzene-1,4-diamine (DTPA) as peripheral groups, two alternative HTMs are reported. Among them, the HTM TPA-DBTDO-DTPA can form a smoother film, which is conducive to the growth of dense perovskite film on it and shows the most suitable energy level. Meanwhile, the sulfonyl unit can passivate the buried defects of perovskite and improve the open-circuit voltage (VOC) of Sn-Pb mixed PSCs. Correspondingly, the TPA-DBTDO-DTPA-based PSC achieves a champion power conversion efficiency of 22.6% and maintains 75.9% of the initial PCE after aging 1000 h in a nitrogen (N2) environment, which fully outperforms the PEDOT:PSS-based control device.

An n‐Doping Cross‐Linkable Quinoidal Compound as an Electron Transport Material for Fully Stretchable Inverted Organic Solar Cells

AbstractThe photocatalytic activity and inherent brittleness of ZnO, which is commonly used as an electron transport layer (ETL) in inverted organic solar cells (OSCs), have impeded advancements in device stability and the development of fully stretchable OSCs. In this study, an intrinsically stretchable ETL for inverted OSCs through a side‐chain cross‐linking strategy has been developed. Specifically, cross‐linking between bromine atoms on the side chains of a quinoidal compound and the amino groups in polyethylenimine resulted in a film, designated QBr‐PEI‐50, with high electrical conductivity (0.049 S/m) and excellent stretchability (crack‐onset strain>45 %). When used as the ETL in inverted OSCs, QBr‐PEI‐50 was markedly superior to ZnO in terms of device performance and stability, yielding a power conversion efficiency (PCE) of 18.27 % and a T80 lifetime exceeding 10000 h. Moreover, incorporation of QBr‐PEI‐50 in fully stretchable inverted OSCs yielded a PCE of 14.01 %, and 80 % of the initial PCE was maintained after 21 % strain, showcasing its potential for wearable electronics.

PTAA‐infiltrated thin‐walled carbon nanotube electrode with hidden encapsulation for perovskite solar cells

AbstractIn perovskite solar cells (PSCs), expensive gold or silver metal has traditionally been utilized as the rear electrode for highly efficient performance. In this context, carbon nanotube (CNT) electrodes have been considered promising rear electrodes because of their excellent electrical conductivity, mechanical strength, and chemical stability in PSCs. Despite these favorable characteristics, concerns have been raised about the power conversion efficiency (PCE) and stability of PSCs based on CNTs due to the porosity of CNT electrodes. In this study, we employed both poly(triarylamine) (PTAA) infiltration and rear electrode hidden encapsulation approaches to address issues related to the porosity of thin‐walled carbon nanotube (TWCNT) electrodes to achieve high efficiency and stability. The infiltration of low‐molecular‐weight PTAA into the TWCNT electrode reduced electrode porosity while simultaneously improving the interfacial contact of the TWCNT layer with the perovskite layer. Furthermore, a novel encapsulation design was employed to prevent air and water exposure of the TWCNT electrode, which significantly enhanced device stability. PSCs with TWCNT rear electrodes developed on the basis of these strategies have the best PCE of 19.5% and show long‐term stability, retaining 96% and 74% of the initial PCE after 225 h at maximum power point tracking under AM 1.5G illumination and 916 h at 85°C/85% relative humidity, respectively.image

A Multisite Atomic‐Oxygen Anchoring Strategy Affords Efficient and Stable Perovskite Solar Cells

AbstractLewis base molecules are widely used to passivate structural defects in perovskites. However, the spatial compatibility between these molecules and the perovskite lattice is seldom considered. Herein, a multisite atomic‐oxygen (O) anchoring passivation strategy using 1,1,2,2‐tetra(4‐methoxyphenyl)ethene (TMPE), which contains four electronegative O atoms to selectively anchor iodine vacancies and passivate under‐coordinated Pb2+ or MA+ defects is proposed. It is found that the distance between any three O atoms in a TMPE molecule matches that of iodine ions in the lattice structure, thereby maximizing passivation effects and enhancing lattice stability. Additionally, the coordination of TMPE facilitates the formation of larger colloid sizes in the precursor solution, effectively regulating crystal growth. Due to the molecular extrusion effect, TMPE‐based anchors localize on the surface, passivating defects and mitigating nonradiative recombination. As a result, defects in MA‐based and FA‐based perovskite films are significantly reduced, achieving optimized power conversion efficiencies (PCEs) of 19.9% and 24.5%, while exhibiting exceptional stability by retaining 90% of initial PCE after 1200 h of storage without encapsulation. This single molecule‐controlled perovskite multisite anchoring strategy would help resolve lattice stability issue caused by perovskite defects, thereby paving the pathway for the development of high‐performance and highly stable perovskite solar cells.

A Universal Ternary Solvent System of Surface Passivator Enables Perovskite Solar Cells with Efficiency Exceeding 26.

Surface passivation is a vital approach to improve the photovoltaic performance of perovskite solar cells (PSCs), in which the passivator solvent is an inevitable but easy-ignored factor on passivation effects. Herein, a universal ternary solvent system of surface passivators is proposed through comprehensively considering the solubility and selective perovskite dissolution of the solvent to maximize the passivation effect. Tetrahydrothiophene 1-oxide (THTO) is selected as the passivation promoter by comparing the binding energy with perovskite and the ability to distort the perovskite lattice among various aprotic polar solvent molecules, which can facilitate the passivator's reaction with perovskite and achieve sufficient passivation on perovskite surface. Besides, chlorobenzene (CB) is used as the diluting agent to minimize the amount of isopropanol (IPA), inhibiting the additional solvent-induced defects. As a result, the planar PSCs achieve a power conversion efficiency (PCE) of 26.05%, (certificated 25.66%). Besides, the unencapsulated devices exhibit enhanced stability, which can maintain 95.23% and 95.68% of their initial PCE after 2000h of storage in ambient air and 800h of light-soaking in N2-glovebox. Moreover, this ternary solvent system also exhibits a well applicability and reliability in different passivator such as PEAI, BAI, and so on.

Non‐Electron Withdrawing Unit Copolymerization to Enhance Photo‐Stability of Thiophene‐Based Organic Solar Cells

The impact of non‐electron withdrawing unit copolymerization on photostability of fullerene‐based organic solar cells is investigated using two donor polymers namely: benzodithiophene‐4,8‐dione (BDD) unit copolymerized with α‐quaterthiophene (4 T) unit (PBDD4T) and poly‐3‐hexyl‐thiophene (P3HT). The optical and electrochemical properties of the polymers reveal a deeper highest occupied molecular orbital (HOMO) and broader absorption in PBDD4T in comparison to P3HT owing to the BDD copolymerization. The copolymer achieves a higher power conversion efficiency (PCE) compared to the P3HT‐based device due to its higher VOC and Jsc that resulted from its deeper HOMO level and broader absorption. The photostability study reveals that PBDD4T‐based devices lost 14% of its initial PCE relative to the 48% reduction in PCE for P3HT‐based devices after 7 h of irradiation. Further investigation into the reasons behind the difference in the photostability suggests that photooxidation and recombination induced by irradiation in PBDD4T‐based devcie are suppressed by BDD‐copolymerization, maintaining better stability. In contrast, P3HT:PC71BM‐based solar absorber shows bimolecular recombination due to photoaging processes, which have negatively impacted the device stability. The reduction in stability of both devices is evident by lower photogenerated current attributed to reduced charge mobility and increased surface roughness.

Surface Reaction Induced Compressive Strain for Stable Inorganic Perovskite Solar Cells

AbstractCesium‐based inorganic perovskites have emerged as promising light‐harvesting materials for perovskite solar cells (PSCs) due to their promising thermal‐ and photo‐stability. However, obstacles to commercialization remain regarding their phase instability. In this work, we report a facile and effective strategy to regulate the surface compressive strain via in situ surface reaction to stabilize CsPbI3 perovskite. The use of a chelating ligand with a molecular configuration closely matching the integer multiples of the unit cell lattice parameters of CsPbI3 induces compressive strain at the surface of CsPbI3. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite phase degradation, thus significantly improving the intrinsic stability of inorganic perovskite. Consequently, enhanced power conversion efficiency (PCE) of 21.0 % and 18.6 % were respectively achieved in 0.16‐cm2 lab‐scale devices and 25.3‐cm2 solar modules. Further, surface reaction enables PSCs with enhanced thermal and operational stability; these devices retain over 95 % of their initial PCE after damp‐heat tests (i.e., in 85 °C and 85 % R. H. air) for 2000 h, and remain 99 % of their initial PCE after operating for 2000 h, representing one of the most stable inorganic PSCs reported so far.

Recrystallizing Sputtered NiOx for Improved Hole Extraction in Perovskite/Silicon Tandem Solar Cells

AbstractSputtering nickel oxide (NiOx) is a production‐line‐compatible route for depositing hole transport layers (HTL) in perovskite/silicon tandem solar cells. However, this technique often results in films with low crystallinity and structural flaws, which can impair electronic conductivity. Additionally, the complex surface chemistry and inadequate Ni3+/Ni2+ ratio impede the effective binding of self‐assembled monolayers (SAMs), affecting hole extraction at the perovskite/HTL interface. Herein, these issues are addressed using a recrystallization strategy by treating sputtered NiOx thin films with sodium periodate (NaIO4), an industrially available oxidant. This treatment improved crystallinity and increased the Ni3+/Ni2+ ratio, resulting in a higher content of nickel oxyhydroxide. These enhancements strengthened the SAM's anchoring capability on NiOx and improved the hole extraction at the perovskite/HTL interface. Moreover, the NaIO4 treatment facilitated Na+ diffusion within the perovskite layer and minimized phase separation, thus improving device stability. As a result, single‐junction perovskite solar cells with a 1.68 eV bandgap achieve a power conversion efficiency (PCE) of 23.22% for an area of 0.12 cm2. Perovskite/silicon tandem cells with an area of 1 cm2 reached a PCE of 30.48%. Encapsulated tandem devices retained 95% of their initial PCE after 300 h of maximum power point tracking under 1‐sun illumination at 25 °C.

Template-Assisted Growth of High-Quality α-Phase FAPbI3 Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS2 Nanosheets.

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA+ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS2 nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS2 as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS2-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.

Vertically Oriented 2D Perovskite Layer with n = 1 Phase Enables Efficient and Stable Inverted Perovskite Solar Cells.

Surface passivation with 2D perovskites has been reported to be important for high-performance perovskite solar cells (PSCs). However, it is challenging to achieve a controlled growth of 2D perovskites, which typically feature random orientation and various n number. In this paper, we fabricate a 2D layer with a highly ordered orientation and pure n = 1 phase on top of the perovskite film using the organic spacer molecule 7-fluoro-1,2,3,4-tetrahydroisoquinolinehydrochloride (7-FTH). The formed 2D perovskites feature a highly ordered orientation normal to the substrate and a pure n = 1 phase, which efficiently passivates surface defects of the as-prepared perovskite films and improves the energy level alignment between the perovskite film and electron transport layer. Consequently, the modified PSCs achieve a champion power conversion efficiency (PCE) of 24.65% with improved VOC and fill factor. After being stored in an N2 glovebox for 1200 h and kept in ambient air (room temperature and relative humidity of 50-70%) for 840 h, the modified devices retain 93% and 95% of its initial PCE, respectively.

Towards device stability of perovskite solar cells through low-cost alkyl-terminated SFX-based hole transporting materials and carbon electrodes

Developing cost-effective, high-efficiency, and stable hole transporting materials (HTMs) is crucial for replacing traditional spiro-OMeTAD in perovskite solar cells (PSCs) and achieving sustainable solar energy solutions. This work presents two novel air-stable HTMs based on a spiro[fluorene-9,9′-xanthene] (SFX) core functionalized with N-methylcarbazole (XC2-M) and N-hexylcarbazole (XC2-H) rings. These HTMs were synthesized via a straightforward, three-step process with good overall yields (∼40%) and low production costs. To further reduce device cost, carbon back electrodes were employed. The resulting PSCs, with a structure of FTO/SnO2/Cs0.05FA0.73MA0.22Pb(I0.77Br0.23)3/HTM/C achieved power conversion efficiencies (PCEs) of 13.5% (XC2-M) and 10.2% (XC2-H), comparable to the reference spiro-OMeTAD device (12.2%). The choice of alkyl chain on the HTM significantly impacts film morphology and device stability. The XC2-H device exhibited exceptional long-term stability, retaining approximately 90% of its initial PCE after 720 h of storage in 30–40% humidity air without encapsulation. This surpasses the performance of both the spiro-OMeTAD (55% retention) and XC2-M (68% retention) devices. The superior stability of XC2-H is attributed to its highly hydrophobic nature and the formation of a compact, smooth film due to interdigitation of the hexyl chains. The straightforward synthesis of XC2-H from commercially available materials offers a promising approach for large-scale PSC production.