High Current Density and Low Hysteresis Effect of Planar Perovskite Solar Cells via PCBM-doping and Interfacial Improvement

Investigation of the Performance of Perovskite Solar Cells with ZnO-Covered PC61BM Electron Transport Layer

Due to its high carrier mobility and electron transmission, the phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) is usually used as an electron transport layer (ETL) in perovskite solar cell (PSC) configurations. However, PC₆₁BM films suffer from poor coverage on perovskite active layers because of their low solubility and weak adhesive ability. In this work, to overcome the above-mentioned shortcomings, 30 nm thick PC₆₁BM ETLs with different concentrations were modeled. Using a 30 nm thick PC₆₁BM ETL with a concentration of 50 mg/mL, the obtained performance values of the PSCs were as follows: an open-circuit voltage (V_oc) of 0.87 V, a short-circuit current density (J_sc) of 20.44 mA/cm², a fill factor (FF) of 70.52%, and a power conversion efficiency (PCE) of 12.54%. However, undesired fine cracks present on the PC₆₁BM surface degraded the performance of the resulting PSCs. To further improve performance, multiple different thicknesses of ZnO interface layers were deposited on the PC₆₁BM ETLs to release the fine cracks using a thermal evaporator. In addition to the pavement of fine cracks, the ZnO interface layer could also function as a hole-blocking layer due to its larger highest occupied molecular orbital (HOMO) energy level. Consequently, the PCE was improved to 14.62% by inserting a 20 nm thick ZnO interface layer in the PSCs.

Near-Ultraviolet Indoor Black Light-Harvesting Perovskite Solar Cells

Indoor light-energy-harvesting solar cells have long-standing history with perovskite solar cells (PSCs) recently emerging as potential candidates with high power conversion efficiencies (PCEs). However, almost all of the reported studies on indoor light-harvesting solar cells utilize white light in the visible wavelength. Low wavelength near-ultraviolet (UV) lights used under indoor environments are not given attention despite their high photon energy. In this study, perovskite solar cells have been investigated for the first time for harvesting energy from a commercially available near-UV (UV-A) indoor LED light (395-400 nm). Also called black lights, these near-UV lights are commonly used for decoration (e.g., in bars, pubs, aquariums, parties, clubs, body art studios, neon lights, and Christmas and Halloween decorations). The optimized perovskite solar cells with the n-i-p architecture using the CH₃NH₃PbI₃ absorber were fabricated and characterized under different illumination intensities of near-UV indoor LEDs. The champion devices delivered a PCE and power output of 20.63% and 775.86 μW/cm², respectively, when measured under UV illumination of 3.76 mW/cm². The devices retained 84.10% of their initial PCE when aged under near-UV light for 24 h. The effects of UV exposure on the device performance have been comprehensively characterized. Furthermore, UV-stable solar cells fabricated with a modified electron transport layer retained 95.53% of its initial PCE after 24 h UV exposure. The champion devices delivered enhanced PCE and power output of 26.19% and 991.21 μW/cm², respectively, when measured under UV illumination of 3.76 mW/cm². This work opens up a novel direction for energy harvesting from near-UV indoor light sources for applications in microwatt-powered electronics such as internet of things sensors.

Functionalizing phenethylammonium by methoxy to achieve low-dimensional interface defects passivation for efficient and stable perovskite solar cells

Low dimensional interface passivation has been proved to be an efficient method to lessen the nonradiative recombination loss in perovskite solar cells. To overcome the limitation of Phenethylammonium (PEA⁺) for carrier transport and water molecule intrusion, we developed a modification strategy by functioning the typical PEA⁺with the 4-methoxy to optimize the interface defects and carrier transport performance, thus maximizing the synchronous improvement of device efficiency and stability. Our results indicate that the 2 mg ml^-14-methoxy-phenethylammonium (MeO-PEA⁺) modified device could achieve a best power conversion efficiency of 19.64% with improved shelf-life stability in ambient conditions. The new passivation molecule of MeO-PEA⁺could possess the capability of defect passivation, carrier transfer, and moisture blocking, demonstrating that rationally designed organic components for interface passivation could help to achieve efficient and stable PSCs.

Donor-Acceptor Competition via Halide Vacancy Filling for Oxygen Detection of High Sensitivity and Stability by All-Inorganic Perovskite Films

Oxygen detection by organic-inorganic halide perovskites (OIHPs) has demonstrated advantages in operating temperature, response time, and reversibility over traditional materials. However, OIHPs can only sense O₂ in light and the unavoidable O₂ exposure during detection easily induces the degradation of OIHPs. The trade-off between sensitivity and stability makes the OIHP-based oxygen sensors impractical. By replacing organic groups with Cs, the compact films of all-inorganic halide perovskites (AIHPs) that can adsorb O₂ at grain boundaries in dark are developed. AIHPs show conductance increase of 1875.5% from 1 × 10^-5 to 700 Torr of O₂ pressure, associated with full reversibility and long-term stability. Combining experiments and modeling, this work reveals the donor-acceptor competition via halide vacancy filling leading to the modulation of carrier concentration and mobility. This work offers understandings on oxygen sensing by perovskite materials and paves the way for further optimization of AIHPs as promising oxygen sensors with high sensitivity and stability.

Bifunctional Ultrathin PCBM Enables Passivated Trap States and Cascaded Energy Level toward Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) with a C₆₀ framework are known for their common drawback of low power conversion efficiency (PCE) of <20% because of nonradiative recombination and inefficient charge transport at their perovskite interfaces. Here, we report an ultrathin [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as a cap layer on perovskite films to overcome this issue. Such a functional cap layer efficiently passivates trap states and establishes a gradient energy level alignment onto perovskite, facilitating the efficient charge transfer and extraction. The as-fabricated inverted PSCs capped with such ultrathin PCBM exhibit a record PCE of 20.07%. After the storage under a N₂ atmosphere for more than 500 h, the PCE of PSCs retains over 85% of its initial level. Our work provides an effective method to upgrade inverted PSCs with the C₆₀ framework with improved efficiency and stability.

Reducing Anomalous Hysteresis in Perovskite Solar Cells by Suppressing the Interfacial Ferroelectric Order

Despite the booming research in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI₃ (FAPbI₃)/TiO₂ and MAPbI₃/phenyl-C61-butyric-acid-methyl-ester (PCBM) heterostructures and explore the correlations between the interfacial ferroelectricity and the hysteresis from the perspective of nonadiabatic electronic dynamics. It is found that the ferroelectric order develops at the MAPbI₃/TiO₂ interface owing to the interaction between the polar MA ions and TiO₂. The polarization switching of the MA ions under an applied gate field would drastically result in different rates in interfacial photoelectron injection and electron-hole recombination, contributing to the undesirable hysteresis. In sharp contrast, ferroelectricity is suppressed at the FAPbI₃/TiO₂ and MAPbI₃/PCBM interfaces, thanks to elimination of the interfacial electric field between perovskite and TiO₂ via substitution of strong polar MA (dipole moment: 2.29 debye) by weak polar FA ions (dipole moment: 0.29 debye) and interface passivation, leading to consistent interfacial electronic dynamics and the absence of hysteresis. The present work sheds light on the physical cause for hysteresis and points to the direction to which the hysteresis could be mitigated in PSCs.

In Situ Passivation on Rear Perovskite Interface for Efficient and Stable Perovskite Solar Cells

Despite the rocketing rise in power conversion efficiencies (PCEs), the performance of perovskite solar cells (PSCs) is still limited by the carrier transfer loss at the interface between perovskite (PVSK) absorbers and charge transporting layers. Here, we propose a novel in situ passivation strategy by using [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) to improve the charge dynamics at the rear PVSK/CTL interface in the n-i-p structure device. A pre-deposited PCBM-doped PbI₂ layer is redissolved during PVSK deposition in our routine, establishing a bottom-up PCBM gradient that is facile for charge extraction. Meanwhile, the surface defects are in situ-passivated via PCBM-PVSK interaction, which substantially suppresses the trap-assisted recombination at the rear interface. Due to the synergistic effect of charge-extraction promotion and trap passivation, the fabricated PSCs deliver a champion PCE of 20.10% with attenuated hysteresis and improved long-term stability, much higher than the 18.39% of the reference devices. Our work demonstrates a promising interfacial engineering strategy for further improving the performance of PSCs.