Enhancing Performance and Stability of Sn-Pb Perovskite Solar Cells with Oriented Phenyl-C61-Butyric Acid Methyl Ester Layer via High-Temperature Annealing.

Phenyl-C61-butyric acid methyl ester (PCBM) can be used as a passivation material in perovskite solar cells (PeSCs) in order to reduce the trap site of the perovskite. Here, we show that a thick PCBM layer can form a smoother surface on the SnO2 substrate, improving the grain size and reducing the microstrain of the perovskite. High-temperature annealing treatment of PCBM layer not only increases its solvent resistance to perovskite precursor or antisolvent, but also enhances its molecular alignment, resulting in improved conductivity as an electron transport layer. High-temperature annealed PCBM (HT-PCBM) effectively minimizes trap-assisted nonradiative recombination by reducing trap density in perovskite and improving the electrical properties at the interface between SnO2 and perovskite layers. This HT-PCBM process significantly enhances the performance of the PeSCs, including the open-circuit voltage (VOC) from 0.39 to 0.77 V, fill factor from 52% to 65%, and power conversion efficiency (PCE) from 6.03% to 15.50%, representing substantial improvements compared to devices without PCBM. This PCE is the highest efficiency among conventional (n-i-p) Sn-Pb PeSCs reported to date. Moreover, passivating the trap sites of SnO2 and separating the interface between the Sn-containing perovskite and the substrate effectively have improved the stability of the Sn-Pb perovskite in the n-i-p structure. The optimized best device with HT-PCBM has maintained an efficiency of over 90% for more than 300 h at 85 °C and 5000 h at room temperature in a glovebox atmosphere.

Role of Charge-Carrier Dynamics Toward the Fabrication of Efficient Air-Processed Organic Solar Cells.

Over the past couple of decades, immense research has been carried out to understand the photo-physics of an organic solar cell (OSC) that is important to enhance its efficiency and stability. Since OSCs undergoes complex photophysical phenomenon, studying these factors has led to designing new materials and implementing new strategies to improve efficiency in OSCs. In this regard, the invention of the non-fullerene acceptorshas greatly revolutionized the understanding of the fundamental processes occurring in OSCs. However, such vital fundamental research from device physics perspectives is carried out on glovebox (GB) processed OSCs and there is a scarcity of research on air-processed (AP) OSCs. This review will focus on charge carrier dynamics such as exciton diffusion, exciton dissociation, charge-transfer states, significance of highest occupied molecular orbital-offsets, and hole-transfer efficiencies of GB-OSCs and compare them with the available data from the AP-OSCs. Finally, key requirements for the fabrication of efficient AP-OSCs will be presented from a charge-carrier dynamics perspective. The key aspects from the charge-carrier dynamics view to fabricate efficient OSCs either from GB or air are provided.

Thickness Tolerance in Large-Area Organic Photovoltaics with Fluorine-Substituted Regioregular Conjugated Polymer.

Large areas and simple processing methods are necessary for the commercialization of organic photovoltaics (OPVs). However, the efficiency drop due to the variation in thickness of OPVs limits their large-scale applications. Regioregular polymers with good crystallinity and packing properties that exhibit high charge mobility and extraction ability can help overcome these limitations. In this study, a regioregular polymer named PDBD-2FBT was synthesized. The crystallinity and packing properties of PDBD-2FBT were enhanced by a simple thermal treatment. Using PDBD-2FBT material as a donor and Y6-HU as an acceptor, we fabricated binary blend OPV devices. The devices with optimized active layer thickness achieved a power conversion efficiency (PCE) of 14.14%. A PCE of 13.18% was maintained even in thick-film conditions (400 nm), and thickness tolerance was observed. Based on the thickness tolerance, a 5-line module measuring 36 cm2 was fabricated via the bar-coating method, and a PCE of approximately 10% was achieved.

Mechanically Stable Flexible Organic Photovoltaics with Silver Nanomesh for Indoor Applications.

Enhanced device performance of flexible organic solar cells (FOSCs) was achieved according to the development of organic solar cells (OSCs). OSCs are promising candidates as energy sources for low-power supply systems such as the Internet of Things (IoT) under indoor lighting environments. To apply FOSCs to flexible or wearable applications, they must be mechanically stable. In this study, we fabricated FOSCs with silver nanomesh (AgNM) as the bottom transparent conductive electrode (TCE). Instead of indium tin oxide (ITO), AgNMs were prepared using three pitches of 25, 50, and 100 µm with a square pattern, using a poly(ethylene terephthalate) (PET) substrate. Notably, the device using AgNMs with a pitch of 25 µm exhibited a power conversion efficiency (PCE) of 14.93% under 1 sun illumination and 17.91% under 1000 lux of light-emitting diode (LED) light conditions. Flexible devices using AgNMs maintained over 92% of their initial PCE under 1 sun illumination (PCE decreased to 12.98 from 14.04%) and over 92% when tested under 1000 lux of LED light illumination (PCE decreased to 16.57 from 17.91%) after 1000 instances of bending. These results demonstrate the advantages of using AgNMs as an alternative TCE under both 1 sun and indoor lightning environments and are promising candidates for flexible applications.

Fullerene-Based Triads with Controlled Alkyl Spacer Length as Photoactive Materials for Single-Component Organic Solar Cells.

Two kinds of dumbbell-shaped acceptor-donor-acceptor (A-D-A)-type triad single-component (SC) photovoltaic molecules based on a benzodithiophene-rhodanine (BDTRh) core and [6,6]-phenyl-C61 butyric acid (PC61BA) termini, BDTRh-C2-PC61BA and BDTRh-C10-PC61BA, were synthesized by modulating the alkyl (C2 and C10) spacer lengths. Both SC photovoltaic structures had similar UV-vis spectra in solution, but BDTRh-C10-PC61BA showed a significantly higher absorption coefficient as a thin film. In films, a more facile intermolecular photo-induced charge transfer was observed for BDTRh-C10-PC61BA in the broad-band transient absorption measurements. BDTRh-C10-PC61BA also exhibited a higher hole mobility (by 25 times) and less bimolecular recombination than BDTRh-C2-PC61BA. By plotting the normalized external quantum efficiency data, a higher charge-transfer state was measured for BDTRh-C10-PC61BA, reducing its voltage loss. A higher power conversion efficiency of ∼2% was obtained for BDTRh-C10-PC61BA, showing higher open-circuit voltage, short-circuit current density, and fill factor than those of BDTRh-C2-PC61BA devices. The different carrier dynamics, voltage loss, and optical and photoelectrical characteristics depending on the spacer length were interpreted in terms of the film morphology. The longer decyl spacer in BDTRh-C10-PC61BA afforded a significantly enhanced intermolecular ordering of the p-type core compared to BDTRh-C2-PC61BA, suggesting that the alkyl spacer length plays a critical role in controlling the intermolecular packing interaction.

High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells.

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices.