awn

A low-cost thiophene-based hole-transporting material, triarylamine-substituted bithiophene (BT-4D), is used as a hole-transporting material in perovskite solar cells with comparable photovoltaic performance to that of 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene. The solar cell using BT-4D demonstrates exceptional long-term stability by retaining 98% of its initial power conversion efficiency after 1186 h under continuous 1-sun illumination in an inert atmosphere.

Abstract

Triarylamine-substituted bithiophene (BT-4D), terthiophene (TT-4D), and quarterthiophene (QT-4D) small molecules are synthesized and used as low-cost hole-transporting materials (HTMs) for perovskite solar cells (PSCs). The optoelectronic, electrochemical, and thermal properties of the compounds are investigated systematically. The BT-4D, TT-4D, and QT-4D compounds exhibit thermal decomposition temperature over 400 °C. The n-i-p configured perovskite solar cells (PSCs) fabricated with BT-4D as HTM show the maximum power conversion efficiency (PCE) of 19.34% owing to its better hole-extracting properties and film formation compared to TT-4D and QT-4D, which exhibit PCE of 17% and 16%, respectively. Importantly, PSCs using BT-4D demonstrate exceptional stability by retaining 98% of its initial PCE after 1186 h of continuous 1 sun illumination. The remarkable long-term stability and facile synthetic procedure of BT-4D show a great promise for efficient, stable, and low-cost HTMs for PSCs for commercial applications.

A robust route simultaneously allows effective defect passivation and reduced energy difference between the valence band edge of the perovskite and the highest occupied molecular orbital of the hole transport layer (HTL) via the judicious placement of strongly polar molecules at the perovskite/HTL interface.

Abstract

The ability to passivate defects and modulate the interface energy-level alignment (IEA) is key to boost the performance of perovskite solar cells (PSCs). Herein, we report a robust route that simultaneously allows defect passivation and reduced energy difference between perovskite and hole transport layer (HTL) via the judicious placement of polar chlorine-terminated silane molecules at the interface. Density functional theory (DFT) points to effective passivation of the halide vacancies on perovskite surface by the silane chlorine atoms. An integrated experimental and DFT study demonstrates that the dipole layer formed by the silane molecules decreases the perovskite work function, imparting an Ohmic character to the perovskite/HTL contact. The corresponding PSCs manifest a nearly 20 % increase in power conversion efficiency over pristine devices and a markedly enhanced device stability. As such, the use of polar molecules to passivate defects and tailor the IEA in PSCs presents a promising platform to advance the performance of PSCs.

The fabrication of fully printed and cost-efficient perovskite solar cells in ambient air–as required for an industrial scalable process is reported. Through multi-objective optimization, fully printed carbon electrode perovskite solar cells and modules are obtained, providing a stable power conversion efficiency of 18.1% and 15.3%, respectively, which is the highest performance of fully printed perovskite devices reported so far.

Abstract

Scalable deposition processes at low temperature are urgently needed for the commercialization of perovskite solar cells (PSCs) as they can decrease the energy payback time of PSCs technology. In this work, a processing protocol is presented for highly efficient and stable planar n–i–p structure PSCs with carbon as the top electrode (carbon-PSCs) fully printed at fairly low temperature by using cheap materials under ambient conditions, thus meeting the requirements for scalable production on an industrial level. High-quality perovskite layers are achieved by using a combinatorial engineering concept, including solvent engineering, additive engineering, and processing engineering. The optimized carbon-PSCs with all layers including electron transport layer, perovskite, hole transport layer, and carbon electrode which are printed under ambient conditions show efficiencies exceeding 18% with enhanced stability, retaining 100% of their initial efficiency after 5000 h in a humid atmosphere. Finally, large-area perovskite modules are successfully obtained and outstanding performance is shown with an efficiency of 15.3% by optimizing the femtosecond laser parameters for the P2 line patterning. These results represent important progress toward fully printed planar carbon electrode perovskite devices as a promising approach for the scaling up and worldwide application of PSCs.

For a solar cell, the spatial distribution of minority carriers plays a key role in determining the recombination flux. By introducing a front surface gradient to push the minority carriers away from the defect-rich surface, a high open-circuit voltage (93% of the Shockley–Queisser limit) and power conversion efficiency (22.36%) are archieved for perovskite solar cells without defect passivation.

Abstract

The recombination flux in a solar cell is determined by not only recombination centers, but also the spatial distribution of minority carriers. For halide perovskite solar cells (PSCs), although there has been a tremendous amount of work focusing on defect passivation, the issue of carrier distribution is not as well studied as for other types of solar cells. Here in this work, with the incorporation of perovskite quantum dots, the concept of the front surface gradient in PSCs using a solution process is successfully realized. Evidenced by multiple characterization techniques, the minority carriers are pushed away from the defect-rich surface by the gradient of valence band maximum, which effectively reduces surface recombination without compromising photocurrent. As a result, the normal structured hybrid PSCs and MAPbI₃ cells exhibit open-circuit voltages exceeding 93% and 90% of their respective Shockley–Queisser limits, and the power conversion efficiencies reach 22.36% and 20.53%, respectively.

Nature Energy, Published online: 07 June 2021; doi:10.1038/s41560-021-00843-4

Publication date: 21 July 2021

Source: Joule, Volume 5, Issue 7

Author(s): Yao Wu, Jing Guo, Wei Wang, Zhihao Chen, Zeng Chen, Rui Sun, Qiang Wu, Tao Wang, Xiaotao Hao, Haiming Zhu, Jie Min

Featuring a fused tricyclic core, an organic small molecule was intentionally synthesized to reduce defects density and improve hole transportation in perovskite devices via π-Pb²⁺ interactions, confirmed by multiple characterizations and simulation.

Abstract

Molecular doping is an of significance approach to reduce defects density of perovskite and to improve interfacial charge extraction in perovskite solar cells. Here, we show a new strategy for chemical doping of perovskite via an organic small molecule, which features a fused tricyclic core, showing strong intermolecular π-Pb²⁺ interactions with under-coordinated Pb²⁺ in perovskite. This π-Pb²⁺ interactions could reduce defects density of the perovskite and suppress the nonradiative recombination, which was also confirmed by the density functional theory calculations. In addition, this doping via π-Pb²⁺ interactions could deepen the surface potential and downshift the work function of the doped perovskite film, facilitating the hole extraction to hole transport layer. As a result, the doped device showed high efficiency of 21.41 % with ignorable hysteresis. This strategy of fused tricyclic core-based doping provides a new perspective for the design of new organic materials to improve the device performance.

Lead halide perovskites are unstable in water due to the high water solubility of the A-site cations present in them. We introduce the intermolecular cation-π interactions between the A-site organic cations in 1D hybrid lead bromide perovskites. The cation-π interactions make these 1D perovskites completely stable in water.

Abstract

Optoelectronically active hybrid lead halide perovskites dissociate in water. To prevent this dissociation, here, we introduce long-range intermolecular cation-π interactions between A-site cations of hybrid perovskites. An aromatic diamine like 4,4′-trimethylenedipyridine, if protonated, can show a long-range cation-π stacking, and therefore, serves as our A-site cation. Consequently, 4,4′-trimethylenedipyridinium lead bromide [(4,4′-TMDP)Pb₂Br₆], a one-dimensional hybrid perovskite, remains completely stable after continuous water treatment for six months. Mechanistic insights about the cation-π interactions are obtained by single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy. The concept of long-range cation-π interaction is further extended to another A-site cation 4,4′-ethylenedipyridinium ion (4,4′-EDP), forming water-stable (4,4′-EDP)Pb₂Br₆ perovskite. These water-stable perovskites are then used to fabricate white light-emitting diode and for light up-conversion through tunable third-harmonic generation. Note that the achieved water stability is the intrinsic stability of perovskite composition, unlike the prior approach of encapsulating the unstable perovskite material (or device) by water-resistant materials. The introduced cation-π interactions can be a breakthrough strategy in designing many more compositions of water-stable low-dimensional hybrid perovskites.

Ascertaining heat energy transfer is essential for the design of organic materials for energy conversion. For Y-series molecules, an extended backbone framework together with advantageous morphologies and suppressed structural disorder trigger more efficient heat diffusion properties. Higher thermal diffusivities enable better spread of phonons to relieve the thermal stress of organic semiconductor devices, leading to enhanced device thermal durability.

Abstract

Efficient heat transfer is beneficial to heat dissipation and the thermal durability of organic solar cell (OSCs). In this regard, heat transfer properties of organic semiconductors within OSCs should play important roles, but their thermal properties are rarely explored. Here, heat diffusion properties of Y-series non-fullerene acceptors processing different DA′D framework, named BZ4F-5, BZ4F-6, and BZ4F-7 are probed; it is found that backbone rings extension from five- to six- and seven-membered-fused rings trigger longer phonon mean free path and higher thermal diffusivities (D) in their pristine solid films and bulk heterojunction blends. Particularly, the correlation between the thermal transport properties in Y-series acceptors and their backbone geometry, molecule stacking, and thin-film crystallinity is demonstrated. More importantly, both organic thin-film transistors and OSCs confirm that thermal durability of organic semiconductor devices correlated with the thermal properties of their active layer. Although BZ5F-6 and BZ4F-7 based devices possess similar device performance at room temperature, superior heat dissipation in BZ4F-7 molecule endows it with enhanced device lifetime. These results contribute to critical design criteria for future molecular optimization in photovoltaic and optoelectronic devices.

A universality strain-regulation approach—crosslinking-enabled strain-regulating crystallization (CSRC)—is introduced to eliminate intrinsic tensile strain in perovskite film, which significantly boosts the perovskite solar cells’ (PSCs) stability and performance. The CSRC approach precisely modulates the perovskite film strain through synchronous cooperation of perovskite crystallization manipulation and in situ chemical crosslinking process, as showcased with several types of crosslinking agents.

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Abstract

α-Formamidinium lead triiodide (α-FAPbI₃) represents the state-of-the-art for perovskite solar cells (PSCs) but experiences intrinsic thermally induced tensile strain due to a higher phase-converting temperature, which is a critical instability factor. An in situ crosslinking-enabled strain-regulating crystallization (CSRC) method with trimethylolpropane triacrylate (TMTA) is introduced to precisely regulate the top section of perovskite film where the largest lattice distortion occurs. In CSRC, crosslinking provides in situ perovskite thermal-expansion confinement and strain regulation during the annealing crystallization process, which is proven to be much more effective than the conventional strain-compensation (post-treatment) method. Moreover, CSRC with TMTA successfully achieves multifunctionality simultaneously: the regulation of tensile strain, perovskite defects passivation with an enhanced open-circuit voltage (V _OC = 50 mV), and enlarged perovskite grain size. The CSRC approach gives significantly enhanced power conversion efficiency (PCE) of 22.39% in α-FAPbI₃-based PSC versus 20.29% in the control case. More importantly, the control PSCs’ instability factor—residual tensile strain—is regulated into compression strain in the CSRC perovskite film through TMTA crosslinking, resulting in not only the best PCE but also outstanding device stability in both long-term storage (over 4000 h with 95% of initial PCE) and light soaking (1248 h with 80% of initial PCE) conditions.

All inorganic perovskite CsPbBr₃ nanocrystals are embedded in bulk Ni₂P phase to form CsPbBr₃/Ni₂P core/shell nanostructures, which significantly improve the photocurrent density up to 10 000 folds and implement highly stable photoelectrochemical water reduction due to the formation of charge channel of Br-P bonds between CsPbBr₃ and Ni₂P.

Abstract

All inorganic perovskite CsPbBr₃ nanocrystals are a promising candidate as photocathode for efficient photoelectrocatalytic (PEC) water splitting. However, the poor chemical stability severely limits its practical applications. The exploration of perovskite-based ideal photocathode materials with efficient and highly stable PEC performance is still an ambitious and meaningful challenge. Herein, under guidance of theoretical calculations, an encapsulation strategy is proposed to prepare the CsPbBr₃/Ni₂P core/shell nanostructures. Compared with the pristine CsPbBr₃ nanocrystals, the CsPbBr₃/Ni₂P nanostructures show a significant improvement of photocurrent density up to 10 000 folds with long-term stability in aqueous solution, and present superior PEC activity for hydrogen generation with nearly 100% faradic efficiency. The encapsulation strategy opens up an avenue for rational design of perovskite-based photocathodes for efficient and stable PEC water reduction.

Herein, a semitransparent flexible MAPbBr₃ perovskite solar cell is demonstrated to be the roof of a greenhouse. It demonstrates a power conversion efficiency (PCE) of 7.67% with an average transmittance of ≈60% in the range of 540–760 nm.

Perovskite photovoltaics (PV) is an emerging thin-film solar energy technology that is advantageous over the currently dominant crystalline silicon PV in terms of its adjustable bandgap with sub-bandgap transparency, potential flexibility, and more rapid continuous roll-to-roll manufacturing, showing promise for unique niche applications. Herein, methylammioun lead tribromide (MAPbBr₃) is utilized in a semitransparent flexible solar cell with a transparent electrode using a sandwiched MoO₃/Au/MoO₃ (MAM) multilayer to harvest around 80% of the visible light region. Through design of the thickness of the MAM multilayer, the reflected light loss is significantly reduced, thereby improving the light transmittance in the visible light region to maximize the photosynthetic yield. The semitransparent flexible device exhibits a power conversion efficiency (PCE) of 7.67% (the highest efficiency of MAPbBr₃-based semitransparent flexible devices), and the opaque rigid MAPbBr₃ solar cell shows a PCE of 9.73% with a high open-circuit voltage of 1.629 V. Optical measurement demonstrates that the flexible cell without metal electrode shows over 77% transparency in the 540–1100 nm range, whereas the overall semitransparent cell shows an average transmittance of 60% in the 540–760 nm range, which is perfect for greenhouse vegetation to not only act as protective coverage but also provide practical output power.

Herein, drift-diffusion simulation parameters are established to describe efficient (20%) p–i–n-type perovskite solar cells. Using these parameters, effective strategies to further improve the performance are explored. It is found that the key to reaching the 30% efficiency milestone is maximizing the built-in voltage across the perovskite layer by implementing doped- or ultrathin transport layers such as self-assembled monolayers.

Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, enabling high power conversion efficiencies (PCEs). However, the precise conditions to advance to an efficiency regime above monocrystalline silicon cells are not well understood. Herein, a simulation model that describes efficient p–i–n-type perovskite solar cells well and a range of different experiments is established. Then, important device and material parameters are studied and it is found that an efficiency regime of 30% can be unlocked by optimizing the built-in voltage across the perovskite layer using either highly doped (10¹⁹ cm⁻³) transport layers (TLs), doped interlayers or ultrathin self-assembled monolayers. Importantly, only parameters that have been reported in recent literature are considered, that is, a bulk lifetime of 10 μs, interfacial recombination velocities of 10 cm s⁻¹, a perovskite bandgap ( E gap ) of 1.5 eV, and an external quantum efficiency (EQE) of 95%. A maximum efficiency of 31% is predicted for a bandgap of 1.4 eV. Finally, it is demonstrated that the relatively high mobile ion density does not represent a significant barrier to reach this efficiency regime. The results of this study suggest continuous PCE improvements until perovskites may become the most efficient single-junction solar cell technology in the near future.

Interfaces provide reactive zones and interphases stabilize electronic device operation. Understanding and designing interfaces and interphases represents an effective and efficient way for developing high-performance rechargeable batteries and perovskite solar cells.

Abstract

The ever-increasing demand for clean sustainable energy has driven tremendous worldwide investment in the design and exploration of new active materials for energy conversion and energy-storage devices. Tailoring the surfaces of and interfaces between different materials is one of the surest and best studied paths to enable high-energy-density batteries and high-efficiency solar cells. Metal-halide perovskite solar cells (PSCs) are one of the most promising photovoltaic materials due to their unprecedented development, with their record power conversion efficiency (PCE) rocketing beyond 25% in less than 10 years. Such progress is achieved largely through the control of crystallinity and surface/interface defects. Rechargeable batteries (RBs) reversibly convert electrical and chemical potential energy through redox reactions at the interfaces between the electrodes and electrolyte. The (electro)chemical and optoelectronic compatibility between active components are essential design considerations to optimize power conversion and energy storage performance. A focused discussion and critical analysis on the formation and functions of the interfaces and interphases of the active materials in these devices is provided, and prospective strategies used to overcome current challenges are described. These strategies revolve around manipulating the chemical compositions, defects, stability, and passivation of the various interfaces of RBs and PSCs.

Publication date: September 2021

Source: Nano Energy, Volume 87

Author(s): Sourabh Pal, Arup Ghorai, Dipak K. Goswami, Samit K. Ray