Photoinduced ion-redistribution in CH3NH3PbI3 perovskite solar cells

High-performance bifacial perovskite solar cells enabled by single-walled carbon nanotubes

Bifacial perovskite solar cells have shown great promise for increasing power output by capturing light from both sides. However, the suboptimal optical transmittance of back metal electrodes together with the complex fabrication process associated with front transparent conducting oxides have hindered the development of efficient bifacial PSCs. Here, we present a novel approach for bifacial perovskite devices using single-walled carbon nanotubes as both front and back electrodes. single-walled carbon nanotubes offer high transparency, conductivity, and stability, enabling bifacial PSCs with a bifaciality factor of over 98% and a power generation density of over 36%. We also fabricate flexible, all-carbon-electrode-based devices with a high power-per-weight value of 73.75 W g-1 and excellent mechanical durability. Furthermore, we show that our bifacial devices have a much lower material cost than conventional monofacial PSCs. Our work demonstrates the potential of SWCNT electrodes for efficient, stable, and low-cost bifacial perovskite photovoltaics.

Defect passivation in methylammonium/bromine free inverted perovskite solar cells using charge-modulated molecular bonding

Molecular passivation is a prominent approach for improving the performance and operation stability of halide perovskite solar cells (HPSCs). Herein, we reveal discernible effects of diammonium molecules with either an aryl or alkyl core onto Methylammonium-free perovskites. Piperazine dihydriodide (PZDI), characterized by an alkyl core-electron cloud-rich-NH terminal, proves effective in mitigating surface and bulk defects and modifying surface chemistry or interfacial energy band, ultimately leading to improved carrier extraction. Benefiting from superior PZDI passivation, the device achieves an impressive efficiency of 23.17% (area ~1 cm2) (low open circuit voltage deficit ~0.327 V) along with superior operational stability. We achieve a certified efficiency of ~21.47% (area ~1.024 cm2) for inverted HPSC. PZDI strengthens adhesion to the perovskite via -NH2I and Mulliken charge distribution. Device analysis corroborates that stronger bonding interaction attenuates the defect densities and suppresses ion migration. This work underscores the crucial role of bifunctional molecules with stronger surface adsorption in defect mitigation, setting the stage for the design of charge-regulated molecular passivation to enhance the performance and stability of HPSC.

An In-Situ Formed Tunneling Layer Enriches the Options of Anode for Efficient and Stable Regular Perovskite Solar Cells

Perovskite solar cells (PSCs) are taking steps to commercialization. However, the halogen-reactive anode with high cost becomes a stumbling block. Here, the halogen migration in PSCs is utilized to in situ generate a uniform tunneling layer between the hole transport materials and anodes, which enriches the options of anodes by breaking the Schottky barrier, enabling the regular PSCs with both high efficiency and stability. Specifically, the regular PSC that uses silver iodide as the tunneling layer and copper as the anode obtains a champion power conversion efficiency of 23.24% (certified 22.74%) with an aperture area of 1.04 cm2. The devices are stable, maintaining 98.6% of the initial efficiency after 500 h of operation at the maximum power point with continuous 1 sun illumination. PSCs with different tunneling layers and anodes are fabricated, which confirm the generality of the strategy.

Solvent Effects on the Structural and Optical Properties of MAPbI3 Perovskite Thin Film for Photovoltaic Active Layer

Controlling the crystallinity, homogeneity, and surface morphology is an efficient method of enhancing the perovskite layer. These improvements contribute toward the optimization of perovskite film morphology for its use in high-performance photovoltaic applications. Here, different solvents will be used in order to process the perovskite precursor, to improve the interfacial contacts through generating a smooth film and uniform crystal domains with large grains. The effect that the solvent has on the optical and structural properties of spin-coated methyl ammonium lead iodide (MAPbI3) perovskite thin films prepared using a single-step method was systematically investigated. The spin-coating parameters and precursor concentrations of MAI and PbI2 were optimized to produce uniform thin films using the different solvents N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). The effect that the solvent has on the morphology of the MAPbI3 films was examined to determine how the materials can be structurally altered to make them highly efficient for use in perovskite hybrid photovoltaic applications. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results show that the synthesized MAPbI3 films prepared using DMSO, DMF, and GBL exhibit the best crystallinity and optical characteristics (photoluminescence (PL)), respectively, of the prepared films. The optical properties resulting from the noticeable improvement PL of the films can be clearly correlated with their crystallinity, depending on the solvents used in their preparation. The film prepared in DMSO shows the highest transmittance and the highest bandgap energy of the prepared films.

Improved highly efficient Dion-Jacobson type perovskite light-emitting diodes by effective surface polarization architecture

Quasi-two-dimensional (quasi-2D) perovskites are emerging as promising materials for highly stable light-emitting diodes (LEDs). However, their lower charge transport mobilities and higher defect densities may constrain their light-emitting efficiency. Here, we combine an excessive-salt-assisted (ESA) process with antisolvent treatments to inhibit the defects in Dion-Jacobson-type perovskite LEDs. Such a method could improve the film quality and recombination efficiency. By further investigation, we found that artificially building a bulk junction interface and enhancing surface polarization could play a more important role in promoting the ability of charge carrier injection and recombination for high-performance LED devices. Accordingly, the DJ-type quasi-2D perovskite LED can achieve a high external quantum efficiency (EQE) of 7.1%.

Impedance Spectroscopy of Metal Halide Perovskite Solar Cells from the Perspective of Equivalent Circuits

Impedance spectroscopy (IS) provides a detailed understanding of the dynamic phenomena underlying the operation of photovoltaic and optoelectronic devices. Here we provide a broad summary of the application of IS to metal halide perovskite materials, solar cells, electrooptic and memory devices. IS has been widely used to characterize perovskite solar cells, but the variability of samples and the presence of coupled ionic-electronic effects form a complex problem that has not been fully solved yet. We summarize the understanding that has been obtained so far, the basic methods and models, as well as the challenging points still present in this research field. Our approach emphasizes the importance of the equivalent circuit for monitoring the parameters that describe the response and providing a physical interpretation. We discuss the possibilities of models from the general perspective of solar cell behavior, and we describe the specific aspects and properties of the metal halide perovskites. We analyze the impact of the ionic effects and the memory effects, and we describe the combination of light-modulated techniques such as intensity modulated photocurrent spectroscopy (IMPS) for obtaining more detailed information in complex cases. The transformation of the frequency to time domain is discussed for the consistent interpretation of time transient techniques and the prediction of features of current-voltage hysteresis. We discuss in detail the stability issues and the occurrence of transformations of the sample coupled to the measurements.