xiaodaibudai

An “S‐shaped, hook‐like” naphthalene diimide derivate, NDI‐BN, is adopted as a cathode interface layer in inverted perovskite solar cells and good power conversion efficiency of 21.32% with enhanced stability is achieved. The relationship between the molecular packing motif of the organic interface layer and the interfacial degradation mechanism is explored.

Abstract

Ion migration induced interfacial degradation is a detrimental factor for the stability of perovskite solar cells (PSCs) and hence requires special attention to address this issue for the development of efficient PSCs with improved stability. Here, an “S‐shaped, hook‐like” organic small molecule, naphthalene diimide derivative (NDI‐BN), is employed as a cathode interface layer (CIL) to tailor the [6,6]‐phenylC61‐butyric acid methylester (PCBM)/Ag interface in inverted PSCs. By realizing enhanced electron extraction capability via the incorporation of NDI‐BN, a peak power conversion efficiency of 21.32% is achieved. Capacitance–voltage measurements and X‐ray photoelectron spectroscopy analysis confirmed an obvious role of this new organic CIL in successfully blocking ionic diffusion pathways toward the Ag cathode, thereby preventing interfacial degradation and improving device stability. The molecular packing motif of NDI‐BN further unveils its densely packed structure with π–π stacking force which has the ability to effectually hinder ion migration. Furthermore, theoretical calculations reveal that intercalation of decomposed perovskite species into the NDI clusters is considerably more difficult compared with the PCBM counterparts. This substantial contrast between NDI‐BN and PCBM molecules in terms of their structures and packing fashion determines the different tendencies of ion migration and unveils the superior potential of NDI‐BN in curtailing interfacial degradation.

WS₂ flakes are introduced as a template for van der Waals epitaxial growth of mixed perovskite films along (001) in perovskite solar cells with an inverted structure. Moreover, the WS₂ interlayer forms a cascade energy alignment in the devices, which favors charge extraction and reduces interfacial recombination. The devices exhibit a power conversion efficiency up to 21.1% along with excellent stability.

Abstract

Organic–inorganic metal halide perovskite solar cells (PSCs) have attracted much research interest owing to their high power conversion efficiency (PCE), solution processability, and the great potential for commercialization. However, the device performance is closely related to the quality of the perovskite film and the interface properties, which cannot be easily controlled by solution processes. Here, 2D WS₂ flakes with defect‐free surfaces are introduced as a template for van der Waals epitaxial growth of mixed perovskite films by solution process for the first time. The mixed perovskite films demonstrate a preferable growth along (001) direction on WS₂ surfaces. In addition, the WS₂/perovskite heterojunction forms a cascade energy alignment for efficient charge extraction and reduced interfacial recombination. The inverted PSCs with WS₂ interlayers show high PCEs up to 21.1%, which is among the highest efficiency of inverted planar PSCs. This work demonstrates that high‐mobility 2D materials can find important applications in PSCs as well as other perovskite‐based optoelectronic devices.

Ambipolar black phosphorene (BP) nanosheets with tailored thicknesses concurrently enhance carrier extraction at both the electron‐transport layer/perovskite and hole‐transport layer/perovskite interfaces for high‐efficiency perovskite solar cells, demonstrating the appealing implementation of BP as a dual‐functional carrier‐transport material for a diversity of optoelectronic devices, including solar cells, photodetectors, sensors, light‐emitting diodes, etc.

Abstract

2D black phosphorene (BP) carries a stellar set of physical properties such as conveniently tunable bandgap and extremely high ambipolar carrier mobility for optoelectronic devices. Herein, the judicious design and positioning of BP with tailored thickness as dual‐functional nanomaterials to concurrently enhance carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces for high‐efficiency and stable perovskite solar cells is reported. The synergy of favorable band energy alignment and concerted cascade interfacial carrier extraction, rendered by concurrent positioning of BP, delivered a progressively enhanced power conversion efficiency of 19.83% from 16.95% (BP‐free). Investigation into interfacial engineering further reveals enhanced light absorption and reduced trap density for improved photovoltaic performance with BP incorporation. This work demonstrates the appealing characteristic of rational implementation of BP as dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, light‐emitting diodes, etc.

Judicious incorporation of ambiopolar black phosphorene with tailored thickness to concurrently impart electron and hole extractions in perovskite solar cells is reported by Jinsong Huang, Zhiqun Lin, and co‐workers in article number https://doi.org/10.1002/adma.2020009992000999. This work underpins the potential implementation of black phosphorene as a dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, and light‐emitting diodes.

Publication date: October 2020

Source: Nano Energy, Volume 76

Author(s): Savas Sonmezoglu, Seckin Akin

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Junsheng Luo, Jianxing Xia, Hua Yang, Chunlin Sun, Ning Li, Haseeb Ashraf Malik, Hongyu Shu, Zhongquan Wan, Haoli Zhang, Christoph J. Brabec, Chunyang Jia

Longevity has been a long-standing concern for hybrid perovskite photovoltaics. We demonstrate high-resilience positive-intrinsic-negative perovskite solar cells by incorporating a piperidinium-based ionic compound into the formamidinium-cesium lead-trihalide perovskite absorber. With the bandgap tuned to be well suited for perovskite-on-silicon tandem cells, this piperidinium additive enhances the open-circuit voltage and cell efficiency. This additive also retards compositional segregation into impurity phases and pinhole formation in the perovskite absorber layer during aggressive aging. Under full-spectrum simulated sunlight in ambient atmosphere, our unencapsulated and encapsulated cells retain 80 and 95% of their peak and post-burn-in efficiencies for 1010 and 1200 hours at 60° and 85°C, respectively. Our analysis reveals detailed degradation routes that contribute to the failure of aged cells.

Publication date: September 2020

Source: Nano Energy, Volume 75

Author(s): Wu-Qiang Wu, Jun-Xing Zhong, Jin-Feng Liao, Chengxi Zhang, Yecheng Zhou, Wenhuai Feng, Liming Ding, Lianzhou Wang, Dai-Bin Kuang

Publication date: September 2020

Source: Nano Energy, Volume 75

Author(s): Faranak Sadegh, Seckin Akin, Majid Moghadam, Valiollah Mirkhani, Marco A. Ruiz‒Preciado, Zaiwei Wang, Mohammad Mahdi Tavakoli, Michael Graetzel, Anders Hagfeldt, Wolfgang Tress

A synthetic polyhalide ligand (2‐picolyl)amine triiodide as a molecular glue is used to passivate halide vacancies at grain boundaries directionally and throughout grain bulk of perovskites. The inverted perovskite solar cells after passivation are allowed to be more efficient, and are profoundly stabilized in both ambient air and light‐soaking circumstances.

The fundamental instability of hybrid perovskite solar cells originates from the considerable halide vacancies. Furthermore, the local roles of halide vacancies between grain boundaries and grain bulk generally conflict, thus inhibiting complete passivation. To overcome this obstacle, a rational polyhalide ligand, di‐(2‐picolyl)amine triiodide, is designed as a molecular “glue” to achieve comprehensive passivation. Unlike a monohalide ligand, this ligand has multiple iodide ions and a quasiplanar tridentate chelation capability, contributing to directional passivation along the grain boundaries and overall passivation throughout the grain bulk. Using this molecular glue passivation, the best inverted solar cell yields an efficiency of 20.02%. Moreover, the relative stability of this cell in ambient air (≈40% humidity, 800 h aging) and under light‐soaking conditions (500 h aging) is profoundly enhanced by 33.33% and 22.26%, respectively. Herein, important insights into the design of passivating molecules to achieve low‐defect perovskites toward the development of multifunctional devices are provided.

An efficient and stable tin perovskite solar cell with a graded heterostructure which is composed of narrow‐bandgap and wide‐bandgap tin perovskites is reported. Such heterostructure facilitates charge extraction and suppresses the oxidation process of Sn²⁺ to Sn⁴⁺. Consequently, the device achieves a maximum power conversion efficiency of 11% with better operational stability.

Lead‐free tin perovskite solar cells (TPSCs) have attracted widespread attention in recent years due to their low toxicity, suitable bandgap, and high carrier mobility. However, the photovoltage and efficiency of TPSCs are still much lower than those of the lead counterparts because of the high trap density and unfavorable band structure in tin perovskite films. To overcome these issues, efficient and stable TPSCs with a graded heterostructure of light‐absorbing layer are reported, in which the narrow‐bandgap tin perovskite dominates at the bulk, whereas the wide‐bandgap tin perovskite is distributed with a gradient from bulk to surface. This heterostructure can selectively extract the photogenerated charge carriers at the perovskite/electron transport layer interface, reduce the density of trap states, and impede the oxidation process of Sn²⁺ to Sn⁴⁺ in air. As a consequence, this graded heterostructure of tin perovskite layer contributes to an increase of 120 mV in the open‐circuit voltage and a maximum power conversion efficiency of 11% for TPSCs with longer operational stability.

A formamidinium derivative, 2‐thiopheneformamidinium (ThFA), is successfully developed and used as a spacer in 2D RP perovskite (ThFA)₂MA _{n −1}Pb _n I_{3 n +1} (nominal n = 3). A precursor organic salts‐assisted crystal growth technique is further developed to prepare high‐quality 2D RP perovskite films, resulting in a high power conversion efficiency of 16.72% with negligible hysteresis and improved stability.

Abstract

Formamidinium (FA)‐based 3D perovskite solar cells (PSCs) have been widely studied and they show reduced bandgap, enhanced stability, and improved efficiency compared to MAPbI₃‐based devices. Nevertheless, the FA‐based spacers have rarely been studied for 2D Ruddlesden–Popper (RP) perovskites, which have drawn wide attention due to their enormous potential for fabricating efficient and stable photovoltaic devices. Here, for the first time, FA‐based derivative, 2‐thiopheneformamidinium (ThFA), is successfully synthesized and employed as an organic spacer for 2D RP PSCs. A precursor organic salts‐assisted crystal growth technique is further developed to prepare high quality 2D (ThFA)₂(MA) _{n −1}Pb _n I_{3 n +1} (nominal n = 3) perovskite films, which shows preferential vertical growth orientations, high charge carrier mobilities, and reduced trap density. As a result, the 2D RP PSCs with an inverted planar p‐i‐n structure exhibit a dramatically improved power conversion efficiency (PCE) from 7.23% to 16.72% with negligible hysteresis, which is among the highest PCE in 2D RP PSCs with low nominal n‐value of 3. Importantly, the optimized 2D PSCs exhibit a dramatically improved stability with less than 1% degradation after storage in N₂ for 3000 h without encapsulation. These findings provide an effective strategy for developing FA‐based organic spacers toward highly efficient and stable 2D PSCs.

In article number https://doi.org/10.1002/aenm.2020006872000687, Qinye Bao and co‐workers systematically investigate the energetics and energy loss in 2D Ruddlesden‐Popper perovskite (RPP) solar cells. The crucial scenario found at the 2D RPP/electron transport layer interface is that the potential gradient across ligands promotes separation of the photogenerated carrier, with electrons transferring from the perovskite crystal to the electron transport layer.

By using a solvent‐mediated phase transformation process, a record certified 21.8% power conversion efficiency in pure‐iodide, alkaline‐metal‐free MA_0.5FA_0.5PbI₃ perovskite‐based solar cells is achieved.

Abstract

Composition and film quality of perovskite are crucial for the further improvement of perovskite solar cells (PSCs), including efficiency, reproducibility, and stability. Here, it is demonstrated that by simply mixing 50% of formamidinium (FA⁺) into methylammonium lead iodide (MAPbI₃), a highly crystalline, stable phase, and compact, polycrystalline grain morphology perovskite is formed by using a solvent‐mediated phase transformation process via the synergism of dimethyl sulfoxide and diethyl ether, which shows long carrier lifetime, low trap state density, and a record certified 21.8% power conversion efficiency (PCE) in pure‐iodide, alkaline‐metal‐free MA_0.5FA_0.5PbI₃ perovskite‐based PSCs. These PSCs show very high operational stability, with 85% PCE retention upon 1000 h 1 Sun intensity illumination. A 17.33% PCE module (6.5 × 7 cm²) is also demonstrated, attesting to the scalability of such devices.

Colloidal synthesis of all inorganic single‐crystalline β‐CsPbI₃ nanorods with an excellent photostability under 45–55% humidity displays the superior characteristics of fabricated inverted perovskite solar cells without any device passivation. Atomic resolution transmission electron micrography reveals the probable distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI₃ nanorod.

Abstract

The synthesis of single‐crystalline β‐CsPbI₃ perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45–55% humidity. The crystal structure of CsPbI₃ NRs films is investigated using Rietveld refined X‐ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (γ‐CsPbI₃) to tetragonal (β‐CsPbI₃) on annealing at 150 °C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI₃ NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline β‐CsPbI₃ NR. The calculation of the electronic band structure of tetragonal β‐CsPbI₃ using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its γ‐phase. An air‐stable (45–55% humidity) inverted perovskite solar cell, employing β‐CsPbI₃ NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the γ‐phase, showing its potential for future low cost photovoltaic devices.

A well aligned CsPbBr₃ micro–nanowire (MW) array is synthesized by controlling the growth of the intermediate CsBr MW array originated from the deposition of the 2D CsPb₂Br₅ phase. Furthermore, a high‐performance photodetector is demonstrated based on the CsPbBr₃ MW array.

Abstract

A large number of derivative phases in inorganic perovskites are reported with special structures and extraordinary performances in photoelectronic device applications. The reverse phase transition between derivative phases and perovskites usually induces recrystallization or forms mixed components. In this work, derivative phase‐induced growth of the CsPbBr₃ micro–nanowire (MW) array by utilizing phase transition of the 2D CsPb₂Br₅ phase is reported. Owing to its layered structure and phase transition, annealing of CsPb₂Br₅ at a temperature of 550 °C combined with solvent quenching leads to a templating effect to form a high‐quality CsBr MW array. Subsequent PbBr₂ deposition and the second annealing are employed to form aligned CsPbBr₃ MW arrays. Based on this method, a CsPbBr₃ MW array‐based photodetector is fabricated. The large grain size, less grain boundaries, and lower surface potential of the CsPbBr₃ MW array lead to high device performance with a responsivity of 7.66 A W⁻¹, a detectivity of ≈10¹² Jones, and long‐term operational stability over 1900 min.

Highly efficient flexible perovskite solar cells prepared by blade coating are reported. A dual hole transport layer comprised of “PEDOT:PSS/PTAA” is delicately designed, which forms a cascade energy level alignment, enabling markedly enhanced charge extraction. In conjugation with a morphology control by additive engineering, the scalable coated flexible solar cell shows an impressive efficiency of 19.41% with a record fill factor of 81%.

Abstract

Halide perovskites are one of the ideal photovoltaic materials for constructing flexible solar devices due to relatively high efficiencies for low‐temperature solution‐processed devices. However, the overwhelming majority of flexible perovskite solar cells are produced using spin coating, which represents a major hurdle for upscaling. Here, a scalable approach is reported to fabricate efficient and robust flexible perovskite solar cells on a polymer substrate. Thiourea is introduced into perovskite precursor solution to modulate the crystal growth, resulting in dense and uniform perovskite thin films on rough surfaces. As a decisive step, a cascade energy alignment is realized for the hole extraction layer by rationally designing a bilayer interface comprised of PEDOT:PSS/PTAA with a distinct offset in the highest occupied molecular orbital levels, enabling markedly enhanced charge extraction and spectral response. An efficiency as high as 19.41% and a record fill factor up to 81% are achieved for flexible perovskite devices processed by a scalable printing method. Equally important, the bilayer interface reinforces the bendability of the indium tin oxide substrate, leading to enhanced mechanical robustness of the flexible devices. These results underpin the importance of morphology control and interface design in constructing high‐performance flexible perovskite solar cells.

In article number https://doi.org/10.1002/adfm.2020010732001073, Hong Meng, Feng Yan, and co‐workers design, synthesize, and successfully use a non‐fullerene electron transport material based on a new spiro derivative, SPS‐4F, in perovskite solar cells, leading to high efficiency as well as good stability of the devices. This work opens a new avenue for developing new spiro‐based electron transport materials and paves a way for realizing high‐performance devices at low costs.

CsPbI₃ perovskite quantum dot (PQD) hybrid nonfullerene organic solar cells are fabricated. The devices based on a PTB7‐Th:FOIC blend with PQDs yield higher efficiency of 13.2% even at near‐zero driving force than that without PQDs (11.6%). Incorporation of PQDs also leads to efficiency enhancement from 15.4% to 16.6% for a PM6:Y6 blend.

Abstract

To take advantages of the intense absorption and fluorescence, high charge mobility, and high dielectric constant of CsPbI₃ perovskite quantum dots (PQDs), PQD hybrid nonfullerene organic solar cells (OSCs) are fabricated. Addition of PQDs leads to simultaneous enhancement of open‐circuit voltage (V _OC), short‐circuit current density (J _SC), and fill factor (FF); power conversion efficiencies are boosted from 11.6% to 13.2% for PTB7‐Th:FOIC blend and from 15.4% to 16.6% for PM6:Y6 blend. Incorporation of PQDs dramatically increases the energy of the charge transfer state, resulting in near‐zero driving force and improved V _OC. Interestingly, at near‐zero driving force, the PQD hybrid OSCs show more efficient charge generation than the control device without PQDs, contributing to enhanced J _SC, due to the formation of cascade band structure and increased molecular ordering. The strong fluorescence of the PQDs enhances the external quantum efficiency of the electroluminescence of the active layer, which can reduce nonradiative recombination voltage loss. The high dielectric constant of the PQDs screens the Coulombic interactions and reduces charge recombination, which is beneficial for increased FF. This work may open up wide applicability of perovskite quantum dots and an avenue toward high‐performance nonfullerene solar cells.

CsPbI₃, with its excellent chemical stability, possesses a suitable bandgap for single‐junction and tandem solar cells, yet the poor phase stability hinders its application. In article https://doi.org/10.1002/adma.2020001862000186, Wan‐Jian Yin, Wallace C. H. Choy, and co‐workers reveal the nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedral rotation and develop a facile method to simultaneously stabilize the photoactive phase and reduce the defect density of the CsPbI₃.