High-performance Inverted Perovskite Solar Cells Research Articles

Bridged Carbolong Modulating Interfacial Charge Transfer Enhancement for High-Performance Inverted Perovskite Solar Cells.

Efficient regulation of perovskite/C60 interface is crucial to improving the long-term stability of the inverted perovskite solar cells (PSCs). However, precise methods for controlling the perovskite/C60 interface have yet to be thoroughly explored. Herein, we develop a carbolong chemical manipulation strategy to improve the interface contact of perovskite/C60 due to versatile functional groups and excellent optoelectronic properties of carbolong metallaaromatics. And constructing an electron-transfer bridge enhances the interfacial interaction and accelerates interfacial electron transfer. The carbolong manipulation results in optimized energy level alignment, suppressed nonradiative recombination, and improved electronic contact. An impressive efficiency of 25.80% is demonstrated, with open-circuit voltage and fill factor of 1.19 V and 84.53%, respectively. The unsealed devices retain more than 98% of their original efficiency after 1400 h of maximum power point tracking under illumination and demonstrate remarkable thermal stability, maintaining 93% of their initial efficiency after 2500 h at 85°C in a nitrogen atmosphere. And the encapsulated carbolong-modified module achieved a high efficiency of 20.72% (active area of 25.25 cm²) with robust operation stability.

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.

Cross-Linkable Fullerene Electron Transport Layer with Internal Encapsulation Capability for Efficient and Stable Inverted Perovskite Solar Cells.

A stable and compact fullerene electron transport layer (ETL) is crucial for high-performance inverted perovskite solar cells (PSCs). However, traditional fullerene-based ETLs like C60 and PCBM are prone to aggregate under operational conditions, a challenge recently recognized by academic and industrial researchers. Here, we designed and synthesized a novel cross-linkable fullerene molecule, bis((3-methyloxetan-3-yl)methyl) malonate-C60 monoadduct (BCM), for use as an ETL in PSCs. Upon a low-temperature annealing at 100 °C, BCM undergoes in-situ cross-linking to form a robust cross-linked BCM (CBCM) film, which demonstrates excellent electron mobility and a suitable band structure for efficient PSCs. Our results show that PSCs incorporating CBCM-based ETL achieve an impressive efficiency of 25.89% (certified: 25.36%), significantly surpassing the 23.25% efficiency of PCBM-based devices. The intramolecular covalent interactions within CBCM films effectively prevent aggregation and enhance film compactness, creating an internal encapsulation layer that mitigates the decomposition and ion migration of perovskite components. Consequently, CBCM-based PSCs show exceptional stability, maintaining 97.8% of their initial efficiency after 1000 hours of maximum power point tracking, compared to only 78.6% retention in PCBM-based devices after less than 820 hours.

Indolo[3,2-b]carbazole-Based Self-Assembled Monolayer Enables High-Performance Inverted Perovskite Solar Cells with Over 25.5% Efficiency

Indolo[3,2-b]carbazole-Based Self-Assembled Monolayer Enables High-Performance Inverted Perovskite Solar Cells with Over 25.5% Efficiency

Low-temperature crosslinked hole transport material for high-performance inverted perovskite solar cells

Hole transport materials (HTMs) play a crucial role in the development of high-performance inverted perovskite solar cells (PSCs) by facilitating hole transport, passivating defects, and tuning crystallization. Achieving high efficiency and stability remains a key challenge for the PSCs. Crosslinked HTMs combine the efficiency of small molecules with enhanced environmental stability, however, a significant challenge in developing crosslinked HTMs for PSCs is the high temperature required for crosslinking. In this work, we synthesized a concise crosslinkable HTM, Tetrastyrenebiphenyldiamine (TPDA), based on a biphenyl core with four styrene groups, using a one-step method. TPDA can be crosslinked through an annealing process at 100℃ for 10 min without the need for any dopants or initiators. Interestingly, the compact films formed in the anneal process and the excellent spreadability for the perovskite precursor solution leading to the high-quality perovskite films, as a result, the inverted devices based on CL-TPDA achieve a champion power conversion efficiency (PCE) of 21.4%. Furthermore, the stability of the devices without encapsulation has notably improved. The PCE maintains over 85% of its initial value after 1000 h of storage in ambient air (25℃, relative humidity about 50%).

Spin-Coated and Vacuum-Processed Hole-Extracting Self-Assembled Multilayers with H-Aggregation for High-Performance Inverted Perovskite Solar Cells.

We report a highly crystalline self-assembled multilayer (SAMUL) that is fundamentally different from the conventional monolayer or disordered bilayer used for hole-extraction in inverted perovskite solar cells (PSCs). The SAMUL can be easily formed on ITO substrate to establish better surface coverage to enhance the performance and stability of PSCs. A detailed structure-property-performance relationship of molecules used for SAMUL is established through a systematic study of their crystallinity, molecular packing, and hole-transporting properties. These SAMULs are rationally optimized by varying their molecular structures and deposition methods through thermal evaporation or spin-coating for fabricating PSCs. The CbzNaphPPA-based SAMUL was chosen for fabricating inverted PSCs due to it exhibiting the highest crystallinity and hole mobility which is derived from the ordered H-aggregation. This resulted in a remarkably high fill factor of 86.45 %, which enables a very impressive power conversion efficiency (PCE) of 26.07 % to be achieved along with excellent device stability (94 % of its initial PCE retained after continuous operation for 1200 h under 1-sun irradiation at maximum power point at 65 °C). Additionally, a record-high PCE of 23.50 % could be achieved by adopting a thermally evaporated SAMUL. This greatly simplifies and broadens the scope for SAM to be used for large-area devices on diverse substrates.

Efficient and Stable Inverted Perovskite Solar Cells Enabled by a Fullerene-Based Hole Transport Molecule.

Designing an efficient modification molecule to mitigate non-radiative recombination at the NiOx/perovskite interface and improve perovskite quality represents a challenging yet crucial endeavor for achieving high-performance inverted perovskite solar cells (PSCs). Herein, we synthesized a novel fullerene-based hole transport molecule, designated as FHTM, by integrating C60 with 12 carbazole-based moieties, and applied it as a modification molecule at the NiOx/perovskite interface. The in-situ self-doping effect, triggered by electron transfer between carbazole-based moiety and C60 within the FHTM molecule, along with the extended π conjugated moiety of carbazole groups, significantly enhances FHTM's hole mobility. Coupled with optimized energy level alignment and enhanced interface interactions, the FHTM significantly enhances hole extraction and transport in corresponding devices. Additionally, the introduced FHTM efficiently promotes homogeneous nucleation of perovskite, resulting in high-quality perovskite films. These combined improvements led to the FHTM-based PSCs yielding a champion efficiency of 25.58% (Certified: 25.04%), notably surpassing that of the control device (20.91%). Furthermore, the unencapsulated device maintained 93% of its initial efficiency after 1000 hours of maximum power point tracking under continuous one-sun illumination. This study highlights the potential of functionalized fullerenes as hole transport materials, opening up new avenues for their application in the field of PSCs.

Optimizing Geometry and ETL Materials for High-Performance Inverted Perovskite Solar Cells by TCAD Simulation.

Due to the optical properties of the electron transport layer (ETL) and hole transport layer (HTL), inverted perovskite solar cells can perform better than traditional perovskite solar cells. It is essential to compare both types to understand their efficiencies. In this article, we studied inverted perovskite solar cells with NiOx/CH3NH3Pb3/ETL (ETL = MoO3, TiO2, ZnO) structures. Our results showed that the optimal thickness of NiOx is 80 nm for all structures. The optimal perovskite thickness is 600 nm for solar cells with ZnO and MoO3, and 800 nm for those with TiO2. For the ETLs, the best thicknesses are 100 nm for ZnO, 80 nm for MoO3, and 60 nm for TiO2. We found that the efficiencies of inverted perovskite solar cells with ZnO, MoO3, and TiO2 as ETLs, and with optimal layer thicknesses, are 30.16%, 18.69%, and 35.21%, respectively. These efficiencies are 1.5%, 5.7%, and 1.5% higher than those of traditional perovskite solar cells. Our study highlights the potential of optimizing layer thicknesses in inverted perovskite solar cells to achieve higher efficiencies than traditional structures.

Trade-off effect of hydrogen-bonded dopant-free hole transport materials on performance of inverted perovskite solar cells

Benefiting from their ordered orientation and superior stability compared to traditional conjugated materials, hydrogen bonding (HB)-induced H-aggregates in organic small molecule hole-transport materials (HTMs) hold a big potential for high-performance inverted perovskite solar cells (IPSCs). However, H-aggregates can also lead to excessive face-aggregation by forming the gaps between aggregates, which is in turn unfavorable for charge mobility and thus for the overall device performance. Herein, we design and synthesize a new set of HB-containing triphenylamine-based small molecules to tailor the degree of H-aggregation, namely O1 (without HB), O2 (unilateral HB unit), and O3 (bilateral HB units). These HTMs make a clear trade-off effect on the charge mobility within the HTM and the interfacial properties of perovskite and HTM. Although the interfacial hole extraction process is promoted upon the HB-functionalized interface, the best performance of IPSCs is still achieved by O1 HTM, which is mainly influenced by the higher hole mobility without HB-induced H-aggregates. Nevertheless, the photo stability of as-fabricated devices is effectively improved upon the HB passivation effect on the interface of HTM (O2 or O3) and perovskite, as well as the better quality of atop perovskite layers with less grain boundary compared to the reference case (O1).

Tailoring cathode interfaces for high-performance perovskite solar cells using perylene diimide derivatives with ionic diversity

Addressing the global demand for clean energy, perovskite solar cells (PVSCs) have emerged as one of the promising candidates. However, ensuring the stability of PVSCs under various environmental factors remains a critical issue for commercialization. Various ionic functionalities are incorporated into perylene diimide (PDIN) derivatives for altering the work function of aluminum electrodes. Well-known amino N-oxide terminal (PDIN-O), and quaternary ammonium salts (PDIN-Br and PDIN-I) were applied as cathode interlayer (CIL) materials in inverted PVSCs. Within the PDIN derivatives, PDIN-I stands out for its superior electron injection effectiveness, minimized energy losses, and enhanced interface contacts, resulting in an optimal device efficiency of 15.9 %. The research emphasizes the role of efficient interlayer engineering in enhancing layer contact and coverage, inhibiting moisture permeation, and improving device stability. PDIN derivatives emerge as eco-friendly alternatives, offering promising prospects for stable and high-performance inverted PVSCs.

Suppressing Ion Migration by Synergistic Engineering of Anion and Cation toward High-Performance Inverted Perovskite Solar Cells and Modules.

Ion migration-induced intrinsic instability and large-area fabrication pose a tough challenge for the commercial deployment of perovskite photovoltaics. Herein, an interface heterojunction and metal electrode stabilization strategy is developed by suppressing ion migration via managing lead-based imperfections. After screening a series of cations and nonhalide anions, the ideal organic salt molecule dimethylammonium trifluoroacetate (DMATFA) consisting of dimethylammonium (DMA+) cation and trifluoroacetate (TFA-) anion is selected to manipulate the surface of perovskite films. DMA+ enables the conversion of active excess and/or unreacted PbI2 into stable new phase DMAPbI3, inhibiting photodecomposition of PbI2 and ion migration. Meanwhile, TFA- can suppress iodide ion migration through passivating undercoordinated Pb2+ and/or iodide vacancies. DMA+ and TFA- synergistically stabilize the heterojunction interface and silver electrode. The DMATFA-treated inverted perovskite solar cells and modules achieve a maximum efficiency of 25.03% (certified 24.65%, 0.1 cm2) and 20.58% (63.74 cm2), respectively, which is the record efficiency ever reported for the devices based on vacuum flash evaporation technology. The DMATFA modification results in outstanding operational stability, as evidenced by maintaining 91% of its original efficiency after 1520 h of maximum power point continuous tracking.

Room-temperature processed plasma activated nickel oxide film for wide-bandgap perovskite solar cells

The nickel oxide (NiOx) film is often employed as a hole transport layer for the production of high-performance inverted perovskite solar cells due to its exceptional chemical stability, high hole mobility, and matching energy level structure. Among various techniques for preparing NiOx, E-beam evaporation-based NiOx films show great promise owing to their low fabrication temperature and excellent photoelectric properties. Herein, an ion bombardment source was used to generate oxygen plasma through the bombardment of oxygen molecules, which subsequently oxidized the non-stoichiometric NiOx. Experimental findings demonstrate that this method substantially enhances the electrical and optical properties of the NiOx film. We utilized a room-temperature-processed NiOx film as a hole transport layer to fabricate inverted wide-bandgap perovskite solar cells, resulting in a champion device efficiency of 17.82%. It is anticipated that the NiOx films produced via this approach will be widely adopted in the industrialization of perovskite solar cells.

Structural modification of fullerene derivates for high-performance inverted perovskite solar cells

This review focuses on the design strategies of fullerenes and their derivatives as electron transport materials in inverted PSCs, and the effects of different application forms on the photovoltaic performance and stability of the devices.

Combining component screening, machine learning and molecular engineering for the design of high-performance inverted perovskite solar cells

To develop efficient and stable inverted perovskite solar cells, we describe an innovative strategy that combines component screening, machine learning and molecular engineering.

Bifunctional Hole-Transport Materials with Modification and Passivation Effect for High-Performance Inverted Perovskite Solar Cells.

Hole-transport materials (HTMs) play an important role in perovskite solar cells (PSCs) to enhance the power conversion efficiency (PCE). The innovation of HTMs can increase the hole extraction ability and reduce interfacial recombination. Three organic small molecule HTMs with 4H-cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) as the central unit was designed and synthesized, namely, CPDTE-MTP (with the 2-ethylhexyl substituent and diphenylamine derivative end-group), CPDT-MTP (with the hexyl substituent and diphenylamine derivative end-group), and CPDT-PMTP (with the hexyl substituent and triphenylamine derivative end-group), which can form bifunctional and robust hole transport layer (HTL) on ITO and is tolerable to subsequent solvent and thermal processing. The X-ray photoelectron spectroscopy (XPS) results proved that CPDT-based HTMs can both interact with ITO through the nitrogen element in them and the tin element in ITO and passivate the upper perovskite layer. It is worth noting that the champion efficiency of MAPbI3 PSCs based on CPDT-PMTP achieved 20.77%, with an open circuit voltage (VOC) of 1.10 V, a short-circuit current (JSC) of 23.39 mA cm-2, and a fill factor (FF) of 80.83%, as three new materials were introduced into p-i-n PSCs as dopant-free HTMs.

Neglected acidity pitfall: boric acid-anchoring hole-selective contact for perovskite solar cells.

The spontaneous formation of self-assembly monolayer (SAM) on various substrates represents an effective strategy for interfacial engineering of optoelectronic devices. Hole-selective SAM is becoming popular among high-performance inverted perovskite solar cells (PSCs), but the presence of strong acidic anchors (such as -PO3H2) in state-of-the-art SAM is detrimental to device stability. Herein, we report for the first time that acidity-weakened boric acid can function as an alternative anchor to construct efficient SAM-based hole-selective contact (HSC) for PSCs. Theoretical calculations reveal that boric acid spontaneously chemisorbs onto indium tin oxide (ITO) surface with oxygen vacancies facilitating the adsorption progress. Spectroscopy and electrical measurements indicate that boric acid anchor significantly mitigates ITO corrosion. The excess boric acid containing molecules improves perovskite deposition and results in a coherent and well-passivated bottom interface, which boosts the fill factor (FF) performance for a variety of perovskite compositions. The optimal boric acid-anchoring HSC (MTPA-BA) can achieve power conversion efficiency close to 23% with a high FF of 85.2%. More importantly, the devices show improved stability: 90% of their initial efficiency is retained after 2400 h of storage (ISOS-D-1) or 400h of operation (ISOS-L-1), which are 5-fold higher than those of phosphonic acid SAM-based devices. Acidity-weakened boric acid SAMs, which are friendly to ITO, exhibits well the great potential to improve the stability of the interface as well as the device.

Simple and robust phenoxazine phosphonic acid molecules as self-assembled hole selective contacts for high-performance inverted perovskite solar cells.

For inverted perovskite solar cells (PSCs), the interfacial defects and mismatched energy levels between the perovskite absorber and charge-selective layer restrain the further improvement of photovoltaic performance. Interfacial modification is a powerful tool for defect passivation and energy level turning by developing new charge-selective materials. Herein, we report three new molecules, 2BrCzPA, 2BrPTZPA, and 2BrPXZPA as self-assembled hole selective contacts (SA-HSCs) by an economical and efficient synthetic procedure. Benefiting from the stronger electron-donating ability of phenothiazine and phenoxazine compared to that of carbazole, 2BrPTZPA and 2BrPXZPA showed more matched energy levels and decreased energy loss. In addition, the ITO substrate coated with 2BrPTZPA and 2BrPXZPA could induce higher-quality perovskite crystal growth without obvious grain boundaries in the vertical direction. Consequently, the corresponding inverted PSCs with decreased trap state density achieved high power convention efficiencies (PCEs) of 22.06% and 22.93% (certified 22.38%) for 2BrPTZPA and 2BrPXZPA, respectively. Furthermore, the 2BrPXZPA-based device with encapsulation retained 97% of the initial efficiency after 600 h of maximum power point tracking under one sun continuous illumination. Finally, 2BrPXZPA was also used for the surface modification of NiOx, and the inverted PSC based on the NiOx/2BrPXZPA bilayer achieved a higher PCE of 23.66% with an open circuit voltage of 1.21 V. This work extends the design strategy of SA-HSCs for efficient and stable inverted PSCs and promotes the commercialization process.

Polar side-chain tuning of perylene diimide and fluorene-based cathode interfacial material for high-performance inverted perovskite solar cells

Cathode interface layers (CILs) play an important role in inverted perovskite solar cells (PVSCs) to correct the mismatched energy levels, improve electron extraction, and passivate interfacial defects.

Heterocyclic D–A–D hole-transporting material for high-performance inverted perovskite solar cells

A new hole-transporting material (HTM) based on benzimidazole–pyridine heterocyclic is synthesized for use in perovskite solar cells. The HTM has good hole transport, lower trap density, and lower electric resistance with a 17.75% efficiency.

One-step synthesis of low-cost perylenediimide-based cathode interfacial materials for efficient inverted perovskite solar cells

Interface engineering plays an important role in improving the performance of perovskite devices. Herein, we reported two perylenediimide small molecular cathode interface materials (CIMs), PDI-2N and PDI-4N, synthesized by a simple method and with good alcohol soluble, which could be used as cathode interfacial layer (CIL) for high-performance inverted perovskite solar cells (PVSCs). The PDI-4N exhibits larger electrical conductivity, electron mobility and self-doping properties than PDI-2N because of more dimethylamino functional groups in the amide positions. Based on these superiorities, a peak PCE of 21.33% with PDI-4N as CIL was achieved, which is the highest PCE for PDI-based interlayer materials as the cathode interlayer in inverted PVSCs. While the PCE with PDI-2N as CIL is only 17.41%. The significant improvement in device efficiency for PDI-4N based device is due to reduced defect density, lower dark current, larger recombination resistance and better surface morphology, which improved charge transport and collection at the PC61BM/Ag interface. Moreover, the ambient stabilities of PVSCs with PDI-2N and PDI-4N as CIL show that the CILs can effectively improve the device stability, and good stability with a PCE loss of only ∼3.0% after 600 h is also obtained. In a word, this work will provide us with molecular design approach by one-step to develop novel cathode interface materials with functional side chains for high-efficiency PVSCs.