Bending-stability Interfacial Layer as Dual Electron Transport Layer for Flexible Organic Photovoltaics

Flexible Organic Photodetectors with Mechanically Robust Zinc Oxide Nanoparticle Thin Films

Zinc oxide nanoparticle (ZnO-NP) thin films have been intensively used as electron transport layers (ETLs) in organic optoelectronic devices, but their moderate mechanical flexibility hinders their application to flexible electronic devices. This study reveals that the multivalent interaction between ZnO-NPs and multicharged conjugated electrolytes, such as diphenylfluorene pyridinium bromide derivative (DFPBr-6), can significantly improve the mechanical flexibility of ZnO-NP thin films. Intermixing ZnO-NPs and DFPBr-6 facilitates the coordination between bromide anions (from the DFPBr-6) and zinc cations on ZnO-NP surfaces, forming Zn²⁺-Br^- bonds. Different from a conventional electrolyte (e.g., KBr), DFPBr-6 with six pyridinium ionic side chains holds the Br^--chelated ZnO-NPs adjacent to DFP⁺ through Zn²⁺-Br^--N⁺ bonds. Consequently, ZnO-NP:DFPBr-6 thin films exhibit improved mechanical flexibility with a critical bending radius as low as 1.5 mm under tensile bending conditions. Flexible organic photodetectors with ZnO-NP:DFPBr-6 thin films as ETLs demonstrate reliable device performances with high R (0.34 A/W) and D* (3.03 × 10¹² Jones) even after 1000 times repetitive bending at a bending radius of 4.0 mm, whereas devices with ZnO-NP and ZnO-NP:KBr ETLs yield >85% reduction in R and D* under the same bending condition.

Enhanced Performance of Flexible Organic Photovoltaics Based on MoS2 Micro-Nano Array

In this work, we investigated the influence of MoS₂ functioning as an electron transport layer (ETL) on the inverted flexible organic photovoltaics (FOPVs). Three ETLs, including MoS₂, lithium quinolate (Liq), and a MoS₂/Liq bilayer, were evaporated onto ITO-integrated polyethylene terephthalate substrates (PET-ITO), and the properties of transmittance, water contact angle, and reflectivity of the films were analyzed. The results revealed that MoS₂ was helpful to improve the lipophilicity of the surface of the ETL, which was conducive to the deposition of the active layer. In addition, the reflectivity of MoS₂ to the light ranging from 400 to 600 nm was the largest among the pristine PET-ITO substrate and the PET-ITO coated with three ETLs, which promoted the efficient use of the light. The efficiency of the FOPV with MoS₂/Liq ETL was 73% higher than that of the pristine device. This was attributed to the nearly two-fold amplification of the MoS₂ array to the light field, which promoted the FOPV to absorb more light. Moreover, the efficiency of the FOPV with MoS₂ was maintained under different illumination angles and bending angles. The results demonstrate the promising applications of MoS₂ in the fabrication of FOPVs.

Achieving efficient and stabilized organic solar cells by precisely controlling the proportion of copolymerized units in electron-rich polymers

A series of random polymers based on the donor polymer PM6 were designed from the perspective of regulating the surface electrostatic potential (ESP) distribution of the polymers and applied in organic solar cells (OSCs). Random polymers with different ESPs were obtained by introducing structural units of polymer PM6 into the polymer structure as the third unit. The simulation results showed that the random polymers feature a wider electron-donating region after the introduction of BDT units, indicating a more efficient charge generation probability. Benefiting from the optimized morphology of the active layer and the stronger interaction between the donor and the acceptor in the active layer, the device exhibited the best charge transport efficiency and lower charge recombination after the introduction of 5% BDT units, and a high power conversion efficiency (PCE) of 16.76% was achieved. In addition, OSC devices based on random polymers incorporating 5% BDT units exhibit excellent device stability. In contrast, the devices based on random polymers after the introduction of BDD units showed a much lower PCE of around 13% due to the inferior charge generation and charge transport. This work not only provides a new perspective for the molecular design of efficient random polymers, but also demonstrates that the OSC devices based on random polymers can still achieve better stability.

Pseudo-Planar Heterojunction Organic Photovoltaics with Optimized Light Utilization for Printable Solar Windows

The existing conformation of the active layer is defective for employment of semitransparent organic solar cells (ST-OSCs) in solar windows. Herein, scalable solar windows are successfully printed by introducing a pseudo-planar heterojunction (PPHJ) structure. The PPHJ structure can effectively improve the average visible transmittance (AVT) value while boosting the power conversion efficiency (PCE) of semitransparent devices due to the reduced optical loss. The universality of the PPHJ structure in the preparation of ST-OSCs is proved. Furthermore, an inset of a superhydrophobic patterned soft insertion layer (PSIL) in the encapsulated window improves the waterproof performance without losing transparency. Accordingly, the semitransparent devices based on the 2,2'-((2Z,2'Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6) system afford a maximal efficiency of 14.62%, with a considerable AVT of 20.42%, and the resultant solar windows achieve a stabilized efficiency of 13.34% with excellent waterproof performance. Moreover, the PCE of the unilateral broken solar windows retains 70.6% of the initial efficiency after being placed under simulated rainfall conditions for 1200 h at room temperature.