hujiao

Herein, we demonstrate a novel two-terminal perovskite/silicon mechanical tandem solar cell, fabricated by bonding a silicon cell upside down on a perovskite cell using a transparent conductive adhesive (TCA). The TCA consists of Ag-coated poly(methyl 2-methylpropenoate) microparticles embedded in a polymer adhesive. The Ag microparticles serve as an electrical current path, and the polymer adhesive mechanically bonds two sub-cells. The specific contact resistance and transmittance of the TCA layer were determined to be 5.46 × 10⁻² Ω∙cm² and >97.0%, respectively. Through an optical simulation, the current of the perovskite top cell was predicted to match the current of the p-type Si bottom cell with an Al back-surface field (BSF) layer when the thickness of MAPbI3 was 150 nm. The tandem cell fabricated under the optimal current matching conditions exhibited a current density of 15.43 mA cm-2, an open-circuit voltage of 1.59 V, and a fill factor of 79%, resulting in a steady-state efficiency of 19.4%. To the best of our knowledge, our result is the highest efficiency among two-terminal mechanical perovskite/silicon tandem cells. The unique structure of this tandem cell facilitates an excellent long-term stability without encapsulation in humid environment.

Graphene has shown many advantages over the metal oxide transparent materials that serve as conventional electrodes in solar cells because graphene is more transparent, has greater stability, and is more mechanically flexible. Flexibility and semi-transparency of the perovskite solar cells are challenged to integrate with the flexible electronic devices since the perovskite solar cells have discovered. Herein, we provide the first report of transfer-free, large-scale monolayer graphene employed as a transparent and flexible bottom electrode. High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate via plasma assisted thermal chemical vapor deposition (PATCVD). Additionally, a highly transparent AZO/Ag/AZO (AAA) multilayer was utilized as a top counter electrode to create semi-transparent perovskite solar cells with a remarkable degree of mechanical flexibility. The 300 nm-thick perovskite solar cells with PATCVD-Graphene revealed a high transmittance of ~26% at a wavelength of 700 nm. The highest level of power conversion efficiency (PCE) (~14.2%) was recorded by an illumination from the bottom graphene side. After 1000 bending cycles under a tensile strain of 1.5%, the graphene-based devices maintained a level of PCE that was more than 90% greater than the initial reading. This superior bending robustness highlights the potential for non-transfer, graphene-based, perovskite photovoltaic material to establish a tandem structure for a foldable solar cell.

Even though the power conversion efficiency (PCE) of plastic perovskite solar cells (P-PSCs) is increased to 18.40%, the majority of solvent systems implemented for deposition of perovskites are hazardous to handle, which will greatly hinder the future development of plastic photovoltaic devices. In this study, composition-tailored hybrid perovskite from a low-toxicity aqueous lead nitrate precursor was fabricated by regulating the conversion kinetics. We systematically investigated the interplay among NO₃⁻ and mixed cation/anion in the intermediate ion exchange and renovated the interpretation of hybrid-composition perovskite conversion. The fully ambient-processed hybrid-composition perovskite with high crystallinity and less defects was applied in a brookite TiO₂ scaffold-based P-PSCs, which achieved a record-high PCE of scaffold-type P-PSC of 16.50%. The interaction of environmentally-friendly aqueous lead nitrate precursor with hybrid ions advanced the understanding of perovskite conversion mechanism and had a great potential to realize the low-toxic fabrication process by using water as a processing solvent in the ambient atmosphere.

Perovskite light-emitting diodes (PeLEDs) have been intensively researched in recent years, and their rapid evolution of efficiency has resulted in their becoming a member of the family of devices with external quantum efficiencies (EQEs) > 20%. In this evolution process, surface engineering was found to be a key factor for obtaining the high-efficiency PeLEDs because of its effects on the state and the density of charge carriers, the density of defects, the transport and the injection of charge, etc. In this review, we mainly focus on recent works on highly efficient PeLEDs based on perovskite 3D/quasi-2D/quantum dots and try to discover the reasons behind their high performance. With continuous optimization of materials and devices, especially with surface engineering, the efficiency of PeLEDs is expected to continue growing and to reach an exciting new level in the near future.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a promising material for utilization in flexible transparent electrodes. However, because the conductivity of PEDOT:PSS is as low as 1 S/cm or even lower, PEDOT:PSS has the inherent problem of a conductivity that is too low for it to be used in the fabrication of flexible, transparent electrodes for use in flexible organic light-emitting devices (OLEDs). Here, we report on hole injection enhancement in a highly conductive Pyronin-B-doped PEDOT:PSS electrode/hexaazatriphenylene hexacarbonitrile (HAT-CN) layer, a strong electron-accepting charge-generation layer, for use in highly efficient flexible OLEDs. While the conductivity of the pristine PEDOT:PSS is 1 S/cm, that of Pyronin-B-doped PEDOT:PSS is significantly increased to 1467 S/cm due to the dramatically enhanced screening effect for PEDOT:PSS films. The energy-band bending barrier at the interface between the Pyronin-B-doped PEDOT:PSS electrode and the HAT-CN layer is significantly decreased compared to that between the pristine PEDOT:PSS electrode and the HAT-CN layer, resulting in improved hole injection. The operating voltage and the current efficiency of the flexible OLEDs with Pyronin-B-doped PEDOT:PSS/HAT-CN electrodes (6.8 V, 26.03 cd/A) are similar to those of OLEDs with ITO/HAT-CN electrodes (7.7 V, 27.95 cd/A). The brightness of the OLEDs after 900 cycles of bending with a radius of curvature of 5 mm is 80% the initial brightness, indicative of the stability of these flexible devices under repeated bendings.

Operational stability remains the foremost concern delaying the commercialization of perovskite solar cells (PSCs). Ions diffusion from iodine-rich perovskite layer to metal electrode is one main reason for the irreversible devices degradation. Here we introduce chemically crosslinked TMTA (trimethylolpropane triacrylate) at both bulk perovskite layer and perovskite/PCBM interface to suppress the ions diffusion toward electrode. The TMTA in perovskite layer suppresses ions migration along grain boundaries and TMTA at perovskite/PCBM interface blocks ions diffusion toward electrode, owing to its continuous network structure and chemically inert nature. Diffusion experiment, permeation experiment and resistive random-access memory (RRAM) investigation confirm the effectively blocked ions diffusion in PSCs with TMTA whether under heat, light or electric field conditions. The resulting PSCs exhibit 7-fold improvement in operational stability at elevated temperature of 60 °C, retaining ~80% of initial efficiency after maximum power point tracking for 1000 h under continuous illumination. The PSCs with TMTA also exhibit good thermal stability and retain over 90% of the initial efficiency after aging at 60 °C for 1000 h.

High-performance, low-power and multifunction-integrated devices are crucial in emerging technologies. Herein, we demonstrate WS₂/CsPbBr₃ van der Waals heterostructure (vdWH) planar photodetectors combining the high mobility of mechanically exfoliated 2D WS₂ nanoflakes with the remarkable optoelectronic properties of 1D single-crystalline CsPbBr₃ nanowires and the strain-gated and strain-sensing characteristics induced by the piezo-phototronic effect. Owing to the effective charge carrier transfer and channel depletion originating from the appropriate energy band alignment, collaborative improvement of the photocurrent and dark current is realized, thus, an ultrahigh on/off ratio of 10^9.83 is achieved. The highest responsivity and detectivity at V_d = 2 V are 57.2 A W⁻¹ and 1.36 × 10¹⁴ Jones, respectively. Even with a lower V_d of 0.5 V, decent performance is still obtained. Furthermore, the interfacial carrier transfer can be manipulated through the piezo-phototronic effect induced by CsPbBr₃ monocrystal nanowires. Thus, when constructed on a flexible PEN substrate, the WS₂/CsPbBr₃ vdWH planar photodetector presents strain-gated photocurrent and responsivity, modulated by a factor of 11.3 with strain application, and a strain-sensing function is simultaneously realized due to the linear dependence of the photocurrent on strain. This unprecedented device design opens up a new avenue toward not only high-performance and low-power but also multifunction-integrated devices realized by the direct effect of mechanical inputs on charge carriers.

High efficiency and long-term stability are vital for further development of perovskite solar cells (PSCs). PSCs based on cesium lead halide perovskites exhibit better stability but lower power conversion efficiencies (PCEs), compared with organic-inorganic hybrid perovskites. Lower PCE is likely associated with trap defects, overgrowth of partial crystals and irreversible phase transition in the films. Here we introduce a strategy to fabricate high-efficiency CsPbBr₃-based PSCs by controlling the ratio of CsBr and PbBr₂ to form the perovskite derivative phases (CsPb₂Br₅/Cs₄PbBr₆) via a vapor growth method. Following post-annealing, the perovskite derivative phases as nucleation sites transform to the pure CsPbBr₃ phase accompanied by crystal rearrangements and retard rapid recrystallization of perovskite grains. This growth procedure induced by phase transition not only makes the grain size of perovskite films more uniform, but also lowers the surface potential barrier that existsbetween the crystals and grain boundaries. Owing to the improved film quality, a PCE of 10.91% was achieved for n-i-p structured PSCs with silver electrodes, and a PCE of 9.86% for hole-transport-layer-free devices with carbon electrodes. Moreover, the carbon electrode-based devices exhibited excellent long-term stability and retained 80% of the initial efficiency in ambient air for more than 2000 h without any encapsulation.

The optimal interface of perovskite solar cells contributes to efficient charge collection and transport for leading high power conversion efficiency. Despite SnO₂ is a commonly used electron transport materials for perovskite solar cells due to wide band gap and n-type semiconducting property, shallow conduction band edge and low electrical conductivity of pristine SnO₂ limit the full potential for efficient electron extraction from perovskite absorber. To improve the electrical property of SnO₂, we design and synthesize Zr-doped SnO₂ nanoparticles, in which tailored electronic structure affords enhanced conductivity, adjusted energy levels and excellence in electron extraction capability. Consequently, the champion device employing Zr-doped SnO₂ nanoparticles achieves a power conversion efficiency of 19.54%, while the pristine SnO₂ nanoparticles yield 17.30% under 100 mW cm⁻² illumination. The systematic device analyses confirm that Zr-doped SnO₂ delivers reduced interfacial resistance, reduced current leakage and suppressed charge recombination, which leads to not only the enhanced power conversion efficiency but also reduced hysteresis for the planar perovskite solar cells.