Opportunities and challenges of hole transport materials for high‐performance inverted hybrid‐perovskite solar cells

Abstract Inverted perovskite solar cells (inverted‐PSCs) have exhibited advantages of longer stability, less hysteresis, and lower fabrication temperature when compared to their regular counterparts, which are important for industry commercialization. Because of the great efforts that have been conducted in the past several years, the obtained efficiency of inverted‐PSCs has almost caught up with that of the regular ones, 25.0% versus 25.7%. In this perspective, the recent studies on the design of high‐performance inverted‐PSCs based on diverse hole transport materials, as well as device fabrication and characterization are first reviewed. After that, the authors moved on to the interface and additive engineering that were exploited to suppress the nonradiative recombination. Finally, the challenges and possible research pathways for facilitating the industrialization of inverted‐PSCs were envisaged

Stabilizing the Ag Electrode and Reducing J-V Hysteresis through Suppression of Iodide Migration in Perovskite Solar Cells

Hysteresis and stability issues in perovskite solar cell (PSCs) hinder their commercialization. Here, we report an effective and reproducible approach for enhancing the stability of and suppressing the hysteresis in PSCs by incorporating a small quantity of two-dimensional (2D) PEA(2)PbI(4) [PEA = C6H5(CH2)(2)NH3] in three-dimensional (3D) MAPbI(3) [MA = CH3NH3] [denoted as (PEA(2)PbI(4)) (MAPbI(3))], where the perovskite films were fabricated by the Lewis acid base adduct method. A nanolaminate structure comprising layered MAPbI(3) nanobricks was created in the presence of 2D PEA(2)PbI(4). For x = 0.017, a power conversion efficiency (PCE) of as high as 19.8% was achieved, which was comparable to the 20.0% PCE of a MAPbI(3)-based cell. Density functional theory (DFT) calculations confirmed that iodide migration was suppressed in the presence of the 2D perovskite as a result of a higher activation energy, which was responsible for the significant reduction in hysteresis and the improved chemical stability against a Ag electrode as compared to the corresponding characteristics of its pristine MAPbI(3) counterpart. An unencapsulated MAPbI(3)-based device retained less than 55% of its initial PCE in a 35-day aging test, whereas a (PEA(2)PbI(4))(0.017)(MAPbI(3))-based device without encapsulation exhibited a promising long-term stability, retaining over 90% of its initial PCE after 42 days.117sciescopu

Task Polar Coordinate Frame-Based Contouring Control of Biaxial Systems

Contouring control is crucial in high-speed and high-precision manufacturing. In this paper, a novel task polar coordinate frame (TPCF), moving along the desired contour, is proposed to naturally calculate and control the estimated contouring error by the circular approximation, a second-order approximation. The dynamics in the world Cartesian coordinate frame is transformed into radial and angular dynamics in the local polar coordinate frame. By the feedback linearization technique and an input feedforward compensation, the closed-loop dynamics are decoupled in terms of the estimated contouring error and the angular error, respectively. Proportional-plus-derivative controllers can be assigned to stabilize the individual axis dynamics in the TPCF. By tuning the control parameters, different strengthening on estimated contouring error and angular error can be imposed explicitly and directly. Various experiments on an XY-stage biaxial system with typical contours, a circle and a figure-"8," were conducted. Comparative studies are carried out for the TPCF- and traditional Frenet frame-based controls. The contouring errors were drastically reduced by the proposed approach, particularly in high-speed and large-curvature contouring cases

Stabilizing the Ag Electrode and Reducing <i>J</i>–<i>V</i> Hysteresis through Suppression of Iodide Migration in Perovskite Solar Cells

Hysteresis and stability issues in perovskite solar cell (PSCs) hinder their commercialization. Here, we report an effective and reproducible approach for enhancing the stability of and suppressing the hysteresis in PSCs by incorporating a small quantity of two-dimensional (2D) PEA₂PbI₄ [PEA = C₆H₅(CH₂)₂NH₃] in three-dimensional (3D) MAPbI₃ [MA = CH₃NH₃ ] [denoted as (PEA₂PbI₄)_<i>x</i>(MAPbI₃)], where the perovskite films were fabricated by the Lewis acid–base adduct method. A nanolaminate structure comprising layered MAPbI₃ nanobricks was created in the presence of 2D PEA₂PbI₄. For <i>x</i> = 0.017, a power conversion efficiency (PCE) of as high as 19.8% was achieved, which was comparable to the 20.0% PCE of a MAPbI₃-based cell. Density functional theory (DFT) calculations confirmed that iodide migration was suppressed in the presence of the 2D perovskite as a result of a higher activation energy, which was responsible for the significant reduction in hysteresis and the improved chemical stability against a Ag electrode as compared to the corresponding characteristics of its pristine MAPbI₃ counterpart. An unencapsulated MAPbI₃-based device retained less than 55% of its initial PCE in a 35-day aging test, whereas a (PEA₂PbI₄)_0.017(MAPbI₃)-based device without encapsulation exhibited a promising long-term stability, retaining over 90% of its initial PCE after 42 days

Stabilizing Buried Interface via Synergistic Effect of Fluorine and Sulfonyl Functional Groups Toward Efficient and Stable Perovskite Solar Cells

Abstract The interfacial defects and energy barrier are main reasons for interfacial nonradiative recombination. In addition, poor perovskite crystallization and incomplete conversion of PbI2 to perovskite restrict further enhancement of the photovoltaic performance of the devices using sequential deposition. Herein, a buried interface stabilization strategy that relies on the synergy of fluorine (F) and sulfonyl (S=O) functional groups is proposed. A series of potassium salts containing halide and non-halogen anions are employed to modify SnO2/perovskite buried interface. Multiple chemical bonds including hydrogen bond, coordination bond and ionic bond are realized, which strengthens interfacial contact and defect passivation effect. The chemical interaction between modification molecules and perovskite along with SnO2 heightens incessantly as the number of S=O and F augments. The chemical interaction strength between modifiers and perovskite as well as SnO2 gradually increases with the increase in the number of S=O and F. The defect passivation effect is positively correlated with the chemical interaction strength. The crystallization kinetics is regulated through the compromise between chemical interaction strength and wettability of substrates. Compared with Cl−, all non-halogen anions perform better in crystallization optimization, energy band regulation and defect passivation. The device with potassium bis (fluorosulfonyl) imide achieves a tempting efficiency of 24.17%

Near-unity quantum yield in zero-dimensional lead-free manganese-based halides for flexible X-ray imaging with high spatial resolution

Low-dimensional luminescent lead-free metal halides have received substantial attention due to their unique optoelectronic properties. Among them, zero-dimensional (0D) manganese (II)-based metal halides with negligible self-absorption have emerged as potential candidates in X-ray scintillators. Herein, we for the first time report a novel lead-free (TBA)2MnBr4 single crystal synthesized via a facile solvent evaporation method. In this crystal, [MnBr4]2− units are isolated by large TBA+ organic cations, resulting in a unique 0D structure. The prepared manganese-based crystals exhibit a bright-green emission centered at 512 ​nm with a high photoluminescence quantum yield (PLQY) of 93.76% at room temperature, originating from the 4T1–6A1 transition of Mn2+. Apart from their outstanding optical performance, the crystals also show excellent stability and can maintain 94.4% of the initial PLQY even after being stored in air for 90 days. Flexible (TBA)2MnBr4 films prepared as X-ray imaging scintillators exhibit a low detection limit of 63.3 nGyair/s, a high light yield of 68000 ​ph/MeV, and a high spatial resolution of 15.4 ​lp/mm. Thus, this work not only enriches the family of lead-free metal halides but also expands the application of manganese (II)-based halides in flexible X-ray scintillators

Interfacial gradient energy band alignment modulation via ion exchange reaction toward efficient and stable methylammonium-free Dion-Jacobson quasi-2D perovskite solar cells

Dion-Jacobson (DJ) quasi-2D perovskite solar cells (PSCs) have attracted significant attention owing to its greater potentials in realizing efficient and stable quasi 2D PSCs as compared to Ruddlesden-Popper counterpart. To further enhance power conversion efficiency (PCE) and stability, the fabrication of methylammonium-free formamidinium (FA)-based DJ quasi-2D PSCs is highly desirable. Herein, we report a strategy for constructing gradient energy band alignment by achieving gradient Br doping (GBD) via in situ ion exchange reaction between I and Br in FA-based DJ quasi-2D PSCs. First, the gradient energy band alignment can facilitate carrier transport, extraction and transfer. Second, the improved crystallinity and reduced defect density due to recrystallization process are realized after FABr treatment. Finally, the incorporation of Br also contributes to increased device stability. The device with GBD achieves a much higher PCE of 16.75% than control device (13.78%), which is mainly as a consequence of a significantly boosted V-OC from 0.970 V to 1.107 V due to suppressed bulk and interfacial nonradiative recombination. The unencapsulated device with GBD maintains 93% of its initial PCE after aging under the relative humidity range of 15-20% for 1600 h, and 91% after aging at 60 degrees C for 400 h.11Nsciescopu