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Despite advances in mixed tin‐lead (Sn‐Pb) perovskite‐based solar cells, achieving both high‐efficiency and long‐term device stability remains a major challenge. Current device deficiencies stem partly from inefficient carrier transport, originating from defects and improper band energy alignment among the device's interfaces. Developing multifunctional interlayer materials simultaneously addressing the above concerns poses an excellent strategy. Herein, through molecular and crystal engineering, an amine‐functionalized C60 mono‐adduct derivative (C60‐2NH3 = bis(2‐aminoethyl) malonate‐C60) is utilized for the synthesis of the first crystalline fullerene‐based 2D metal halide semiconductor, namely (C60‐2NH3)Pb2I6. Single crystal XRD studies elucidated the structure of the new material, while DFT calculations highlighted the strong contribution of C60‐2NH3 to the electronic density of states of the conduction band of (C60‐2NH3)Pb2I6. Utilization of C60‐2NH3 as an interlayer between a FA0.6MA0.4Pb0.7Sn0.3I3 perovskite and a C60 layer offered superior band energy alignment, reduced nonradiative recombination, and enhanced carrier mobility. The corresponding perovskite solar cell (PSC) device achieved a power conversion efficiency (PCE) value of 21.64%, maintaining 90% of its initial efficiency, after being stored under a N2 atmosphere for 2400 h. This work sets the foundation for developing a new family of functional materials, namely Fullerene Metal Halide Semiconductors, targeting applications from photovoltaics to catalysis, transistors, and supercapacitors. [ABSTRACT FROM AUTHOR]

Interface defect is a limiting factor of the charge dynamics and stability of perovskite solar cells (PSCs). Herein, a rare earth metal oxide cerium oxide is introduced into the interface between perovskite and spiro‐OMeTAD [2,2,7,7‐tetrakis (N,N ‐di‐p‐methoxyphenyl‐amine) 9,9‐spirobifluorene] to passivate interfacial defects. Due to the nearest‐neighbor interaction of CeO2 with spiro‐OMeTAD, it can accelerate the oxidization process of spiro‐OMeTAD to form a donor–acceptor complex at this interface, which can overcome the interface barrier for the high hole collecting ability. The bonding formation between lead and oxygen makes this heterojunction show metal conduction behavior at this interface. The insertion of CeO2 between perovskite and spiro‐OMeTAD, can improve hole transferring to balance the extraction of electron and hole by their respective electrodes, for the decreased device hysteresis with the higher efficiency and improved stability. The results show that the CeO2‐based PSC device achieve a power conversion efficiency (PCE) of over 24%, retaining more than 87% of the initial PCE after 2570 h of storage at 20 ≈ 30% humidity. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) with a light‐harvesting three‐dimensional perovskite bulk layer as backbone component have achieved great progress in performance. Nonradiative recombination is one major place to improve efficiency and stability as they cause significant energy loss in PSCs. Additionally, an imperfection in grain boundaries will initiate device degradation. One of the most successful strategies to decrease nonradiative recombination in PSCs is the introduction of reduced dimensional perovskite (e.g., perovskite quantum wells), benefiting the device's efficiency and stability tremendously. Here, instead of quantum wells, mixed‐cation perovskites with ligand‐contained CsPbBrxI3 − x quantum dots (QDs) are prepared, which is shown to function as perovskite healing "surface patches." Benefiting from the "surface patches" effect, the QDs‐film shows reduced defects and enhancing film quality which lead to the excellent performance of solar cells (enhancing the power conversion efficiency from 19.21% of the control device to 21.71% [22.1% in reverse scan]). [ABSTRACT FROM AUTHOR]

External encapsulation technique as a straightforward craft process has been adopted to prevent the infiltration of moisture and oxygen, thereby improving environmental stabilities of lead halide perovskite solar cells (PSCs). However, irreversible light‐induced degradation originating from various vacancies and ion diffusion or migration inside the device cannot be efficiently solved by external encapsulation. Herein, an internal encapsulation strategy by introducing NbCl5 at the buried tin oxide/perovskite interface and spin‐casting n‐butylammonium bromide on top of perovskite is developed to comprehensively passivate the vacancies and hence block the channels for ion diffusion or migration. The internal encapsulation strategy results in better homogeneous electron transport layer and effective vacancy passivation at the buried interface and simultaneously generates a more homogeneous, better crystallized perovskite in the vertical direction with significantly reduced residual PbI2. Furthermore, fewer oxygen vacancies and formation of ultrathin Nb2O5 lead to a better interfacial energy level alignment for electron transfer. As a result, power conversion efficiency (PCE) of the resulting PSCs is as high as 24.01%. More importantly, the device demonstrates an excellent stability, retaining 88% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm–2 white light illumination at ≈55 °C temperature, in N2 atmosphere) after 1000 h. [ABSTRACT FROM AUTHOR]

Abstract: SnO2 has been well investigated in many successful state‐of‐the‐art perovskite solar cells (PSCs) due to its favorable attributes such as high mobility, wide bandgap, and deep conduction band and valence band. Several independent studies show the performances of PSCs with SnO2 are higher than that with TiO2, especially in device stability. In 2015, the first planar PSCs were reported with a power conversion efficiency over 17% using a low temperature sol‐derived SnO2 nanocrystal electron transport layer (ETL). Since then, many other groups have also reported high performance PSCs based on SnO2 ETLs. SnO2 planar PSCs show currently the highest performance in planar configuration devices (21.6%) and are close to the record holder of TiO2 mesoporous PSCs, suggesting their high potential as ETLs in PSCs. The main concerns with the application of SnO2 as ETL are that it suffers from degradation in high temperature processes and that its much lower conduction band compared to perovskite may result in a voltage loss of PSCs. Here, notable achievements to date are outlined, the unique attributes of SnO2 as ETLs in PSCs are described, and the challenges facing the successful development of PSCs and approaches to the problems are discussed. [ABSTRACT FROM AUTHOR]

Organo‐metal halide hybrid perovskites with mixed cations and halides have become promising photovoltaic materials, showing extraordinary optoelectronic properties and excellent device performance. Herein, an organic semiconducting nonfullerene acceptor (NFA) molecule IT‐M is introduced as Lewis base to improve perovskite interfaces. This facile Lewis base‐assisted strategy effectively enhances the electronic properties of Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 thin films, passivates the perovskite surface defects and further boosts the performance of perovskite solar cells. With the reduced surface defects, this approach significantly enhances the charge transport properties and boosts the photogenerated photoluminescence lifetime from 1.46 to 2.20 µs. As a result, the n‐i‐p planar perovskite solar cell champion efficiency reaches 20.5% with a high FF of 81%. Moreover, the Lewis base molecule IT‐M can also passivate the under‐coordinated lead ions and enhance the durability of perovskite PbI6 octahedra framework under an ambient environment with thermal stress and humidity. The results provide a simple while highly effective route of fabricating the high performance and stable planar perovskite solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Planar perovskite solar cells (PSCs) based on low‐temperature‐processed (LTP) SnO2 have demonstrated excellent photovoltaic properties duo to the high electron mobility, wide bandgap, and suitable band energy alignment of LTP SnO2. However, planar PSCs or mesoporous (mp) PSCs based on high‐temperature‐processed (HTP) SnO2 show much degraded performance. Here, a new strategy with fully HTP Mg‐doped quantum dot SnO2 as blocking layer (bl) and a quite thin SnO2 nanoparticle as mp layer are developed. The performances of both planar and mp PSCs has been greatly improved. The use of Mg‐SnO2 in planar PSCs yields a high‐stabilized power conversion efficiency (PCE) of close to 17%. The champion of mp cells exhibits hysteresis free and stable performance with a high‐stabilized PCE of 19.12%. The inclusion of thin mp SnO2 in PSCs not only plays a role of an energy bridge, facilitating electrons transfer from perovskite to SnO2 bl, but also enhances the contact area of SnO2 with perovskite absorber. Impedance analysis suggests that the thin mp layer is an “active scaffold” selectively collecting electrons from perovskite and can eliminate hysteresis and effectively suppress recombination. This is an inspiring advance toward high‐performance PSCs with HTP mp SnO2. [ABSTRACT FROM AUTHOR]

Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO‐modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron–hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn‐doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole‐blocking layer exhibits a remarkable improvement of all J–V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification. [ABSTRACT FROM AUTHOR]

Although the perovskite solar cells (PSCs) based on organic hole transport materials (HTMs) have demonstrated excellent photovoltaic performance, there are still some obstacles that limiting their future commercialization, one of which is the device stability. Herein, we first report that depositing a (200) orientated PbS thin film upon organic HTMs as buffer layer can significantly enhance the stability and improve the performance of PSCs. The superior hole extraction efficiency of spiro-OMeTAD/PbS bilayer can balance the charge transfer and the hydrophobic nature of PbS could avoid the permeation of moisture. As a result, the PSCs with PbS buffer layer exhibited a better photovoltaic performance (a champion power conversion efficiency of 19.58%) with respect to the reference cells (18.79%), and maintained almost 100% of its initial PCE after 1000 h stored in ambient air. Furthermore, when suffer from some more severe conditions, the device with PbS retained 56% of its initial PCE after 96 h annealing at 85 °C, while only 25% for the reference cells. Our results provide a simple method to avoid the weakness of organic HTMs, and suggest that PbS thin film could be an alternative buffer layer material in PSCs to simultaneously improve the device stability and photovoltaic performance. [ABSTRACT FROM AUTHOR]

Solution-processed hole transporting materials (HTMs) that are dopant-free show promise for use in low-cost, high-performance perovskite solar cells (PSCs). The highest-efficiency PSCs use organic HTMs, many of which have low mobilities and therefore require doping, which lowers the device stability. Additionally, these materials are not easily scaled because they often require complicated synthesis. Two new HTMs ( IDT- TPA and IDTT- TPA) were synthesized, which contained either an extended fused-ring indacenodithiophene ( IDT) or indacenodithienothiophene (IDTT) core and strong electron-donating methoxytriphenylamine (TPA) groups as the end-capping units. The extended conjugation in the backbone of IDTT- TPA resulted in stronger π-π interactions (3.321 Å) and a higher hole mobility of 6.46×10−4 cm2 V−1 s−1 when compared with that of IDT- TPA (9.53×10−5 cm2 V−1 s−1). A dopant-free, planar PSC that contained IDTT- TPA was fabricated and exhibited a high power conversion efficiency (PCE) of 15.7 %. This cell exhibited a higher PCE and less hysteresis than devices that contained IDT- TPA. [ABSTRACT FROM AUTHOR]

Interface engineering is critical for achieving high‐efficiency and high‐stability perovskite solar cells (PSCs). Herein, a new interface engineering approach—poly(ethylene oxide) (PEO) modification of SnO2 quantum dot (QD) film—to improve electron transport is introduced. It is found that when the PEO film is annealed over its glass‐transition temperature, the ether‐oxygen unshared electron pair in the PEO film activates to form a crosslinking complex with metal ions at the SnO2 QD and perovskite interface, which triggers heterogeneous nucleation over the perovskite precursor film and is beneficial for achieving uniform and dense perovskite films. PEO is also shown to passivate the bulk defects of perovskite films and the interface defects between SnO2 QD and perovskite, which promotes electron‐transferring from the perovskite layer to cathode. PSCs based on SnO2 QD with PEO treatment exhibit an enhanced efficiency, leading to a champion PCE of 20.23%, with good reproducibility and stability. [ABSTRACT FROM AUTHOR]

We demonstrate two octamethyl-substituted phthalocyanines, HMe 2 Pc and ZnMe 2 Pc, as dopant-free hole-transport layers for planar pervoskite solar cells. HMe 2 Pc illustrated a very similar HOMO energy level and a slightly smaller band gap compared with that of ZnMe 2 Pc, resulting in perovskite photovoltaic devices with very close open circuit voltage ( V OC ) values based on different phthalocyanine hole transporting materials. Varying the central metals also leads to the HMe 2 Pc film exhibiting higher carrier mobility, better film coverage, and stronger surface hydrophobicity than the ZnMe 2 Pc film, which is consistent with higher short circuit current density ( J SC ) and fill factor ( FF ) values, and better long-term film stability for HMe 2 Pc-based devices. When employed as hole-transport layers by vacuum deposition, the HMe 2 Pc-based devices showed the highest photo conversion efficiency (PCE) of up to 15.59%, which is slightly higher than the 14.88% PCE for ZnMe 2 Pc-based devices. These properties make the easily-synthesized and highly stable octamethyl-substituted phthalocyanines promising candidates as hole-transport materials in perovskite solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrostatic self-assembly SnO 2 QDs-TQDs composite materials were fabricated. • SnO 2 QDs-TQDs could effectively engineer the ETL and perovskite/ETL interface. • TQDs modified perovskite exhibits reduced defect density and passivated grain boundaries. • PCE of 23.47 % for PSCs, responsivity (35.54 mA W−1) and response speed (154 ms) for PPDs were achieved. The performance of perovskite solar cells and photodetectors strongly depends on the carrier extraction in the electron transport layer/perovskite interface and the film quality of the perovskite layer. Ti 3 C 2 T x MXene quantum dots, which exhibit both good conductivity of MXene materials and size-dependent tunable optoelectronic properties of quantum dots, were synthesized to form electrostatic self-assembly nanoparticles and further introduced into perovskite optoelectronic devices. The carrier extraction in electron transport layer/perovskite interface was significantly improved, and the defect density of the modified perovskite layer was effectively reduced. These improvements ultimately lead to a remarkable power conversion efficiency of perovskite solar cells increasing from 16.57 % to 23.47 %, and the photodetectors achieve responsivity approaching 35.54 mA W−1 and response speed of 154 ms (rise time) and 120 ms (decay time). Meanwhile, the long-time humidity, thermal and light stress stability of the devices were largely boosted, which originated from the better crystallization and suppressed degradation of the perovskite films. [ABSTRACT FROM AUTHOR]

Dopant engineering involving molecular/ionic additives is a kind of usual technique to achieve state-of-the-art perovskite solar cells (PSCs) with favorable stability. It is critical to maximize the functions of doping agents for perovskite due to its unstable structure, inherent defect, weak water resistance, and so on. To ameliorate these problems, herein, we introduce a multi-functional halogen-free cesium trifluoroacetate (CsCF 3 COO, CsTFA) into organic amine salt precursor via a conventional two-step sequential deposition approach. The carboxyl group (-COO-) of CsTFA can passivate inherent traps that exist in perovskite crystal lattice through interacting with the Pb–I framework, which effectively suppresses non-radiative recombination and further reduces open-circuit voltage deficit. Cesium ion (Cs+) supplies an A-site cation to tune tolerance factor while the trifluoromethyl section (-CF 3) improves hydrophobicity of devices. These three synergistic effects finally drive the power conversion efficiency of the champion device from 21.1% to 22.3% with improved stability. This work paves a new way to enhance the performance and the stability of photovoltaic device using halogen-free doping materials. • A halogen-free cesium trifluoroacetate is introduced to supply A-site cation. • Carboxyl group can interact with Pb–I framework, thereby passivating traps. • Trifluoromethylated configuration contained in CsTFA can improve hydrophobicity. • Synergistic effects deliver the champion device a 22.3% efficiency. [ABSTRACT FROM AUTHOR]

Tin oxide (SnO 2) as an electron transport layer (ETL) has made impressive achievements in planar-structure heterojunction perovskite solar cells (PSCs). However, the improvement of the SnO 2 quality, connected with its trap density, electrical conductivity and band energy alignment, is still worth concerning. The quality of the SnO 2 film especially from wet coating techniques is quite sensitive to the environment conditions in the preparation process thus leading to poor repeatability. High repeatability of every functional layer fabrications is one of the basic requirements toward commercialization for PSCs. Herein, we add hydrogen peroxide (H 2 O 2) into the SnO 2 precursor solution (denoted as H 2 O 2 –SnO 2) to enable the quality improvement of ETL. The resultant H 2 O 2 –SnO 2 film exhibits less trap density, improved electrical conductivity, outstanding film fabrication repeatability and better energy level alignment, leading to significantly higher charge carrier extraction and reduced device hysteresis effect. By employing H 2 O 2 –SnO 2 ETL, PSCs with excellent repeatability and performance uniformity deliver a champion power conversion efficiency (PCE) of 22.15% with negligible hysteresis, and show impressive long-term stability. This research paves a new way for the further performance enhancement of planar PSCs and the higher quality modified SnO 2 may find applications in other opto-electronic devices. • Hydrogen peroxide was introduced to passivate defects of SnO 2 as ETL in PSCs. • The PSCs using hydrogen peroxide-modified SnO 2 ETL exhibited better repeatability. • The PSCs of hydrogen peroxide-modified SnO 2 ETL delivered a PCE of 22.15%. • The stability of PSCs with hydrogen peroxide-modified SnO 2 ETL was prolonged. [ABSTRACT FROM AUTHOR]