Efficient Hole Transport Research Articles

Enhancing hole-transport efficiency in (CH3NH3)2CuClxBr4-x perovskite solar cells through functionalization of multi-walled carbon nanotubes

This study addresses the conductivity limitation of conventional hole-transporting layers (HTLs) like Spiro-OMeTAD in perovskite solar cells. We integrate functionalized multi-walled carbon nanotubes (MWCNTs) into Spiro-OMeTAD and examine the impact of chemical oxidation/functionalization of MWCNTs on their application in perovskite solar cells. Various ratios of H2SO4/HNO3 mixture were employed to functionalize MWCNTs, with FTIR analysis confirming functional group attachments on the nanotube walls. Raman spectroscopy was utilized to analyze defect formation in the MWCNTs, while FESEM images displayed both the tubular structure and morphological alterations resulting from functionalization. XRD analysis was conducted to examine the structural variances resulting from different functionalization ratios. A lead-free copper-based perovskite (CH3NH3)2CuBr4-xClx (x = 0.5), synthesized via a straightforward solution method, served as the active material for solar cells. The XRD assessment of the active material confirmed perovskite formation, with morphological analysis revealing a layered structure. Diffuse Reflectance Spectroscopy (DRS) measurements yielded a bandgap of approximately 1.86 eV for the perovskite. Dark I–V measurements were executed for Spiro-OMeTAD films incorporated with pure and functionalized MWCNTs, showcasing improved conductivity attributed to charge carrier conduction via defect passivation. Hybrid solar cells were fabricated with structures such as TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/Spiro-OMeTAD/Ag, and TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/functionalized MWCNTs/Spiro-OMeTAD/Ag. These cells demonstrated enhanced stability, retaining over 65 % of their initial efficiency after 10 days of storage, attributed to improved moisture permeability inferred from contact angle measurements and XRD analysis. Photovoltaic characterization revealed significant improvements in fill factor (∼70 %), short-circuit current density (2.94 mA), open-circuit voltage (0.70 V), and power conversion efficiency (PCE) (1.6 %) for the FTO/TiO2/(CH3NH3)2CuCl0·5Br3.5/Spiro-MWCNT-1/Ag device.

Leveraging Phenazine‐Based Ligands for Optimized Perovskite Optoelectronic Performance Through Chelation and Redox Engineering

AbstractPerovskite nanocrystals (PNCs) hold immense potential for optoelectronic and photovoltaic applications. However, their performance is hindered by surface defects that promote non‐radiative recombination and reduce stability. Surface engineering, particularly through defect passivation, is crucial for achieving high‐performing perovskite solar cells. Chelation has been shown to significantly improve the efficiency and stability of perovskite solar cells. In this study, a novel chelation strategy using 1,10‐Phenanthroline (Phen) is presented as a bidentate chelating ligand to effectively target and passivate these detrimental surface defects. By strategically designing a Phenanthroline derivative, dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine (Phen‐derivative) with optimized redox potentials, dual functionality: efficient defect passivation and hole transport is achieved. X‐ray photoelectron spectroscopy (XPS) confirms the superior binding capability of the Phen‐derivative due to chelation. This strong interaction facilitates efficient and ultrafast charge transfer from PNCs and the formation of a long‐lived charge‐separated state, as evidenced by sustained bleaching in transient absorption spectra. A metal‐dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine complex (Ir‐complex) derived from dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine, but lacking a chelation site, hinders desired hole transfer despite similar charge transfer energetics. This work emphasizes the critical role of chelation‐mediated interfacial interactions and energy alignment in designing effective charge shuttle molecules and unlocking the potential of lead‐chelating hole transporters for next‐generation light‐harvesting technologies.

Molybdenum-Oxide-Modified PEDOT:PSS as Efficient Hole Transport Layer in Perovskite Solar Cells.

Over the last ten years, there has been a remarkable enhancement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs), with poly (3,4-ethylenedioxythiohene):poly (styrenesulfonate) (PEDOT:PSS) emerging as a prevalent choice for the hole transport layer (HTL). Nevertheless, the evolution of the widely utilized PEDOT:PSS HTL has not kept pace with the swift advancements in PSC technology, attributed to its suboptimal electrical conductivity, acidic nature, and inadequate electron-blocking performance. This study presents a novel approach to enhance the HTL by introducing molybdenum oxide (MoO3) into the PEDOT:PSS, leveraging the conductivity and solution processing compatibility of MoO3. Two methods for MoO3 integration were explored: an ammonium molybdate tetrahydrate (AMT) precursor and the direct addition of MoO3 nanoparticles. The carrier dynamics of PSCs modified by MoO3 are significantly optimized. Therefore, the PCE of the device modified by AMT and molybdenum oxide is increased to 18.23 and 19.64%, respectively, and the stability of the device is also improved. This study emphasizes the potential of MoO3 in contributing to the development of more efficient and stable PSCs.

Improving redox reactions of Spiro-OMeTAD via p-type molecular scaffold to reduce energy loss at Ag-electrode in perovskite solar cells

2,2’,7,7’-Tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9’-spirobifluorene (Spiro) is an essential hole-transport material used in perovskite solar cells (PSCs). However, the redox reaction of Spiro and its impact at the interface with the metal electrode are not yet fully understood. In this study, we introduced a crystalline additive (CA) to regulate the redox process of Spiro and its interface with an Ag electrode. Our findings indicate that CA functions as a molecular scaffold, improving the crystallinity and stability of radicals in Spiro throughout the entire redox reaction. This enhancement increases the hole mobility of Spiro and strengthens the internal electric field, thereby improving hole extraction and transport efficiency at both interfaces. Moreover, the optimized redox reaction of Spiro reduces energy loss at the Ag electrode, significantly boosting the power conversion efficiency to 25.21%. Furthermore, CA mitigates the aggregation of lithium salt and enhances the stability of the device. Our findings contribute to a deeper understanding of hole-transport mechanisms of Spiro and emphasize the importance of reducing energy loss at the Spiro/Ag electrode interface in PSCs.

Modification of Copper-based chalcogenide nanocrystals' interconnections for efficient hole transportation in perovskite solar cell

Cu-based chalcogenide p-type semiconductors in the form of nanocrystals can be used to deposit low-temperature and stable hole-transport layers (HTL) for n-i-p perovskite solar cells (PSCs). In this study, the synthesis parameters are modified to improve the hole-extraction of CuIn0.75Ga0.25S2 (CIGS) layer. By optimizing the amount of oleylamine as the capping agent, the internal series resistance of PSCs decreases significantly while preventing aggregation of CIGS nanocrystals. Increasing the growth temperature from 220°C to 275°C leads to an increase in the size of CIGS nanocrystals. This results in an improvement in the open-circuit voltage of PSCs with FTO/c-TiO2/m-TiO2/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/CIGS/Au structure from 0.941 to1.092 V, and Fill Factor from 60 to 73 on average. Finally, a nanocomposite of CIGS and a small amount of doped Spiro-OMeTAD is applied in PSCs with ITO/SnO2/(FA,MA)Pb(I,Cl,Br)3/HTL/Au structure. The achieved efficiency of 18.72% is comparable to that of PSCs with highly doped Spiro OMeTAD (18.5%).

Synergistic Effect of Defects Passivation and Energy Level Alignment Realizing P3HT-Based High-Efficiency CsPbI3 Perovskite Solar Cells.

Poly (3-hexylthiophene) (P3HT) is one of the most efficient hole transport layers (HTLs) in perovskite solar cells (PSCs). However, surface and boundary defects in CsPbI3, and energy level mismatch between CsPbI3 and P3HT lead to a low power conversion efficiency (PCE) in P3HT-based CsPbI3 PSCs. Here, a synergistic strategy with anti-solvent (sec-pentyl alcohol, 2-PA) and passivators (LiX, X = F, Cl, Br, I) is developed to promote the photovoltaic performance of P3HT-based CsPbI3 PSCs. It is proved that the 2-PA washes away the residual DMF and DMAPbI3, and assists the secondary growth of CsPbI3 crystal. LiX not only can passivate iodine (I) vacancies, but also can reduce energy offset at CsPbI3/P3HT interface, accelerating hole extraction process. Finally, an impressive efficiency of 19.26% is obtained due to the synergistic effect of defects passivation and energy alignment, which is 34.4% higher than the 14.32% achieved in Control cell. These findings prove that synergistic strategy of defects passivation and energy alignment is an effective way for realizing high-efficiency in P3HT-based CsPbI3 PSCs.

An efficient hole transport layer and novel citrate-FeCo(OH)x cocatalyst co-modified Ti-Fe2O3 photoanode towards boosting photoelectrochemical water oxidation

The restricted performance of α-Fe2O3 in photoelectrochemical (PEC) water splitting is currently constrained by the slow kinetics of water oxidation and the rapid charge recombination. Herein, we prepared a composite photoanode with molecular copper phthalocyanine (CuPc) as the hole transport layer and citric acid assisted FeCo(OH)x as the cocatalyst using a simple two-step method. The optimized Ti-Fe2O3/CuPc/citrate-FeCo(OH)x photoanode achieved an photocurrent density of 2.67 mA/cm−2 at 1.23 V vs. RHE, which is 6.5 times higher than pure Ti-Fe2O3 and can maintain long-term stability. Detailed studies have shown that CuPc and Ti-Fe2O3 can form an interface electric field for hole oriented transport, significantly improving the transfer of photogenerated carriers. The FeCo(OH)x coating assisted by citric acid deposition not only forms a conformal coating, but also acts as a bifunctional layer to quickly transfer holes from Ti-Fe2O3/CuPc to the electrolyte. It also significantly increases the reactive active sites and hydrophilicity of Ti-Fe2O3/CuPc, which further accelerates the water oxidation kinetics. This study provides a promising strategy for the development of an efficient and cost-effective photoanode and extends the design concept of a PEC water splitting device.

Efficient hole transport layers for silicon heterojunction solar cells by surface plasmonic modification in MoOx/Au NPs/MoOx stacks

This study explores the integration of Au nanoparticles (NPs) into molybdenum oxide (MoOx) thin films to form a MoOx/Au NPs/MoOx (MAM) stack. This stack serves as a hole transport layer (HTL) in silicon heterojunction solar cells, aiming to address the challenges of safety concerns and inefficient carrier transport. Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy spectra demonstrate that the incorporation of Au NPs notably raises the work function of MAM to 5.85 eV and stabilize Mo6+ concentrations at 94.07%. In addition, Au NPs effectively act as a shield against detrimental interactions with Ag, thereby improving the interfacial stability between the back electrode and HTL. This strategic enhancement facilitates the formation of surface plasmon polaritons, reduces the contact resistance to 41.19 mΩ cm2, and boosts the quantum efficiency by injecting hot electrons and intensifying the surface electric field. These advancements lead to a significant enhancement in the fill factor and short-circuit current, leading to the development of a heterojunction solar cell with an increased efficiency (Eff) from 19.81% to 22.03%. This investigation underscores the transformative potential of engineered nanomaterials in elevating the performance and stability of photovoltaic devices, promoting the wider adoption of renewable energy technologies.

Doping bilayer hole-transport polymer strategy stabilizing solution-processed green quantum-dot light-emitting diodes.

Quantum-dot light-emitting diodes (QLEDs) are solution-processed electroluminescence devices with great potential as energy-saving, large-area, and low-cost display and lighting technologies. Ideally, the organic hole-transport layers (HTLs) in QLEDs should simultaneously deliver efficient hole injection and transport, effective electron blocking, and robust electrochemical stability. However, it is still challenging for a single HTL to fulfill all these stringent criteria. Here, we demonstrate a general design of doping-bilayer polymer-HTL architecture for stabilizing high-efficiency QLEDs. We show that the bilayer HTLs combining the electrochemical-stable polymer and the electron-blocking polymer unexpectedly increase the hole injection barrier. We mitigated the problem by p-doping of the underlying sublayer of the bilayer HTLs. Consequently, green QLEDs with an unprecedented maximum luminance of 1,340,000 cd m-2 and a record-long operational lifetime (T95 lifetime at an initial luminance of 1000 cd m-2 is 17,700 hours) were achieved. The universality of the strategy is examined in various polymer-HTL systems, providing a general route toward high-performance solution-processed QLEDs.

Solvent management and Li+/Mg2+ co-doping enable efficient n-i-p NiOx-based perovskite solar cells

Spin-coating pre-fabricated NiOx nanocrystals using an annealing-free process is a compatible technique for fabricating the hole transport layer in n-i-p structured perovskite solar cells. The solvothermal method, assisted by long-chain fatty acids or amines such as oleic acid and oleylamine, has demonstrated the applicability of fabricating NiOx nanoparticles with uniform morphology and size. However, the long-chain fatty acids or amines covering the NiOx nanoparticles cannot be removed at low temperature, obstructing the transport of photo-generated holes due to their insulating characteristics. Herein, triphenylphosphine is employed to replace a portion of oleylamine in the solvothermal reaction solution. Experimental results demonstrate that the introduction of triphenylphosphine does not affect the dispersion of the synthesized NiOx nanoparticles in toluene. The as-fabricated n-i-p structured device receives an efficiency of 12.63 %. Thereafter, Li+ doping and Li+-Mg2+ co-doping strategies are used to further enhance the devices' performance. The best-behaved device with Li+-Mg2+ co-doping NiOx hole transport layer acquires an efficiency of 16.20 %. This research provides a practical approach for fabricating efficient NiOx hole transport materials for n-i-p structured perovskite solar cells.

End-group modification in a fluorene-terminated efficient hole transport materials for organic and perovskite solar cells

End-group modification in a fluorene-terminated efficient hole transport materials for organic and perovskite solar cells

Design of Next‐Generation Tin‐Based Perovskite Photodetector with Enhanced Spectral Responsivity for Eco‐friendly Applications

This study introduces an environment‐friendly perovskite photodetector (PPD) utilizing the inorganic–organic perovskite CH3NH3SnI3 as the light‐absorbing layer. Perovskite materials, known for their exceptional optoelectronic properties, hold significant promise in photodetector fabrication. The proposed device architecture strategically employs NiO and TiO2 layers to facilitate efficient hole and electron transport. The CH3NH3SnI3‐based PPD demonstrates outstanding quantum efficiency across the visible spectrum, extending into infrared regions. It exhibits a responsivity of 0.68 A W−1 and a detectivity of 3.81 × 1013 Jones. Comprehensive defect and temperature analyses are performed to understand the behavior of the proposed device. These results underscore the potential of less toxic perovskite alternatives for high‐performance photodetectors. All simulations are conducted using the SCAPS‐1D simulator to ensure the validity of the findings.

Improving the power conversion efficiency of RbPbBr3 absorber based solar cells through the variation of efficient hole transport layers

Novel rubidium-lead-bromide (RbPbBr3) hybrid perovskite solar cells (HPSCs) are gaining attention from researchers because of their exceptional semiconductor qualities. Researchers have been examining RbPbBr3-based single junction photovoltaic cells in a number of configurations, including two different hole transport layers (HTL) made of V2O5 and MoTe2 and an electron transport layer (ETL) made of CdS. We investigated elements including band alignment, defect density, layer thickness, doping concentration, interface defect density, carrier concentration, generation, recombination, open circuit voltage (VOC), short circuit current (JSC), fill factor (FF), and power conversion efficiency (PCE) through extensive numerical analysis using SCAPS-1D simulation software. According to the research, the V2O5 HTL design, with a VOC of 1.1433 V, a JSC of 34.3969 mAcm−2, and an FF of 86.63 %, attained the maximum PCE at 34.06 %. By contrast, the MoTe2 HTL configuration's PCE was 31.66 %, with a VOC of 1.0388 V, a JSC of 34.4977 mAcm−2, and an FF of 88.35 %. These results provide insightful information and a workable strategy for creating RbPbBr3-based, reasonably priced thin-film solar cells.

Efficient Perovskite Solar Cells Enabled by Facile Synthesis of Triphenylamine‐Based Hole‐Transport Material with D–A1–A2 Structure

In perovskite solar cells (PSCs), the selection of the hole‐transport material (HTM) markedly influences both the achievement of high efficiency and overall stability. This study outlines the synthesis of a dopant‐free HTM founded on the donor–acceptor1–acceptor2 (D–A1–A2)‐conjugated structure and its integration into PSCs. The ensuing PSCs showcase a power conversion efficiency of 17.8%, comparable to NiOx inorganic HTM‐based devices and surpassing poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate polymeric HTM‐based devices. The efficiency comparable to NiOx is attributed to the efficient hole extraction and transport facilitated by the conjugated π junctions in the specifically designed structure. Furthermore, these devices exhibit enhanced stability, maintaining 95% of their initial performance for 60 d in an N2 atmosphere without encapsulation. The improved stability primarily arises from the hydrophobic nature of the HTM. The larger π‐conjugated molecules lead to a denser film by reducing intermolecular space, effectively retarding water intrusion and providing superior protection to the perovskite layer. Thus, the dopant‐free D–A1–A2 HTM with an extended conjugated π structure not only effectively enhances device efficiency but also substantially improves device stability.

Ag:PSS polyelectrolyte/PTB7 bilayers as efficient hole transport layers for perovskite solar cells

By virtue of the exceptional optical and electrical features of organic-inorganic lead-halide perovskites, the power conversion efficiency (PCE) of perovskite solar cells (PeSCs) has surpassed that of commercialized single junction silicon solar cells. Although PeSCs have demonstrated exceptional efficiency, there is still room for improvement to approach the theoretical Shockley-Queisser limit. Additionally, there is a need for the development of cost-effective strategies to produce high-performance devices, enabling PeSCs to fulfill their potential as a widely adopted and sustainable energy source.Considering this, in this work, we’ve developed a polyelectrolyte (silver poly(styrene sulfonate (PSS)) (Ag:PSS) hole transport layer (HTL), and investigated it in combination with a conjugated polymer,poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b]-dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl] (PTB7) as a bilayer HTL. Ag:PSS alone performs poorly due to mismatched energy levels at the anode interface, however, when PTB7 is used in combination with Ag:PSS, effective extraction and transport of carriers towards the anode is achieved. PeSCs with optimized bilayer HTLs (Ag:PSS/PTB7) gave PCEs of up to 17.09 %, higher than that of the Ag:PSS alone (reference device 12.13 %) which can be attributed to improved interfacial energetics at the HTL/perovskite interface.

Insights into the role of Co3O4/Ti3C2 MXene hybrid material in photoelectrochemical water oxidation over BiVO4 photoanode

Developing efficient hole transport layers and water oxidation electrocatalysts is vital for improving the performance of photoelectrochemical (PEC) devices for water-splitting. In this work, we synthesized Co3O4 nanoparticles/Ti3C2-MXene hybrid material and utilized it as a dual-function material to transport the photogenerated holes and catalyze the water oxidation reaction. It was found that the modification of BiVO4 with Co3O4/Ti3C2-MXene prolonged the lifetime of the photogenerated holes by 13.7-fold (i.e. from 0.26 s for BiVO4 to 3.56 s for Co3O4/Ti3C2/BiVO4) and significantly reduced the charge transfer resistance. The modification of BiVO4 with only Ti3C2-MXene resulted in significant surface recombination more likely due to the high concentration of the accumulated holes in the Mxene layer because of its low electrocatalytic activity toward water oxidation reaction. Employing the Co3O4/Ti3C2-MXene hybrid material significantly reduced the rate constant of surface recombination and dramatically enhanced the charge transfer efficiency (i.e. from 0.17% for BiVO4 to 14.0% for Co3O4/Ti3C2/BiVO4 at 0.65 VRHE). Under optimized conditions, the Co3O4/Ti3C2/BiVO4 photoanode was able to deliver 5.05 mA cm−2 at 1.23 VRHE and outperforms Ti3C2/BiVO4 and Co3O4/BiVO4 photoanodes. Moreover, it showed high stability for over 50 hours and reached a Faradaic efficiency of 90%. An applied bias photo-to-current efficiency (ABPE) value of 1.71% at 0.62 VPt was obtained for the overall water splitting. This work provides a facile method to reduce surface recombination and enhance the stability and PEC efficiency of BiVO4 photoanodes via the modification with dual-function oxygen evolution catalyst/hole transport layer hybrid material.

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.

Performance Improvement of Formamidinium‐Based Perovskite Photodetector by Solution‐Processed C8‐BTBT Modification

AbstractOrganic–inorganic hybrid perovskite has attracted extensive research due to its excellent optoelectronic properties and is a competitive candidate material for a new generation of photodetectors. However, lateral structure photodetectors based only on perovskite active materials still present moderate performance and poor stability. Herein, lateral structure formamidinium‐based perovskite FA0.9Cs0.1PbI3 photodetectors are reported which are modified by a solution‐processed organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) layer for improved photosensitive performance and ambient/flexibility stability. High‐mobility organic semiconductor C8‐BTBT serves as an efficient hole transport layer that fills the grain boundaries and gaps of the FA0.9Cs0.1PbI3 film, enabling rapid extraction and transport of the photo‐generated carriers from the perovskite to the electrodes, resulting in enhanced photosensitive performance of the photodetector. Compared with the original device, the C8‐BTBT‐modified photodetector exhibits dramatically improved performance with a best responsivity of 1278 mA W−1, specific detectivity of 1.58 × 1012 Jones, external quantum efficiency of 298%, and fall time of 14.09 ms, which is 10.84 times less than 152.76 ms of the pure perovskite device. Moreover, the C8‐BTBT film acts as a protective layer for the FA0.9Cs0.1PbI3 film because of its good air stability and effective coverage, which significantly improves the ambient stability of the perovskite photodetector compared with the original device, increasing photocurrent retention from 2.5% to 61.5% or 81.5% at different humidity after 6 days. Furthermore, the C8‐BTBT‐modified perovskite photodetector exhibits outstanding flexibility performance, with only a 5% reduction in photocurrent under bending and almost no change after 200 bending cycles, while those of the pristine perovskite device have degraded to ≈80% and ≈75% under the same conditions, respectively. This study provides a facile and effective solution‐processed‐based strategy for constructing high‐performance and stable perovskite photodetectors.

Stable and efficient perovskite solar cells based on tert-butyl peroxy-2-ethylhexanoate modified hole transport layer

Nowadays, perovskite solar cells (PSCs) have gained significant attention as one of the most promising new energy technologies. However, the application of spiro-OMeTAD, a highly efficient organic hole transport material (HTM) in PSCs, is limited due to its inherent weaknesses in conductivity and hole mobility. Here, a free radical initiator, tert-butyl peroxy-2-ethylhexanoate (TBPEH) is introduced to induce the rapid and controllable oxidation of Spiro. TBPEH-modified hole transport layer (HTL) produces more free radical cations, increasing carrier mobility and electrical conductivity. A smoother surface of the modified HTL improves the charge transport efficiency. Additionally, trap-state density and defect-induced nonradiative recombination of TBPEH-modified device are decreased. In addition, better energy level matching between the HTL and perovskite layer enables more efficient hole transport. Consequently, the PSC doped with TBPEH achieves a champion power conversion efficiency (PCE) of 24.33 %, surpassing the PCE of 21.72 % obtained from the pristine device. Furthermore, the TBPEH-modified devices show better stability. Storing in the atmosphere at 30 % relative humidity for 42 days, the TBPEH-modified device maintains 90.8 % of its highest efficiency, compared to the 73.8 % of the pristine one.

Custom-tailored hole transport layer using oxalic acid for high-quality tin-lead perovskites and efficient all-perovskite tandems.

All-perovskite tandem solar cells (TSCs) have exhibited higher efficiencies than single-junction perovskite solar cells (PSCs) but still suffer from the unsatisfactory performance of low-bandgap (LBG) tin-lead (Sn-Pb) subcells. The inherent properties of PEDOT:PSS are crucial to high-performance Sn-Pb perovskite films and devices; however, the underlying mechanism has not been fully explored and revealed. Here, we report a facile oxalic acid treatment of PEDOT:PSS (OA-PEDOT:PSS) to precisely regulate its work function and surface morphology. OA-PEDOT:PSS shows a larger work function and an ordered reorientation and fiber-shaped film morphology with efficient hole transport pathways, leading to the formation of more ideal hole-selective contact with Sn-Pb perovskite for suppressing interfacial nonradiative recombination losses. Moreover, OA-PEDOT:PSS induces (100) preferred orientation growth of perovskite for higher-quality Sn-Pb films. Last, the OA-PEDOT:PSS-tailored LBG PSC yields an impressive efficiency of up to 22.56% (certified 21.88%), enabling 27.81% efficient all-perovskite TSC with enhanced operational stability.