Impact of substituents on the performance of small-molecule semiconductors in organic photovoltaic devices via regulating morphology

This review summarizes recent prominent examples of substituent engineering on small-molecule organic semiconductors for photovoltaic applications, focusing on flexible substituents that regulate the active-layer morphology.

Stretchable transparent electrodes for conformable wearable organic photovoltaic devices

To achieve adhesive and conformable wearable electronics, improving stretchable transparent electrode (STE) becomes an indispensable bottleneck needed to be addressed. Here, we adopt a nonuniform Young’s modulus structure with silver nanowire (AgNW) and fabricate a STE layer. This layer possesses transparency of >88% over a wide spectrum range of 400–1000 nm, sheet resistance below 20 Ω sq−1, stretchability of up to 100%, enhanced mechanical robustness, low surface roughness, and good interfacial wettability for solution process. As a result of all these properties, the STE enables the fabrication of a highly efficient ultraflexible wearable device comprising of both organic photovoltaic (OPV) and organic photodetector (OPD) parts with high mechanical durability and conformability, for energy-harvesting and biomedical-sensing applications, respectively. This demonstrates the great potential of the integration of OPVs and OPDs, capable of harvesting energy independently for biomedical applications, paving the way to a future of independent conformable wearable OPV/OPDs for different applications.

Optimized Stoichiometry for CuCrO2 Thin Films as Hole Transparent Layer in PBDD4T-2F:PC70BM Organic Solar Cells

The performance and stability in atmospheric conditions of organic photovoltaic devices can be improved by the integration of stable and efficient photoactive materials as substituent of the chemically unstable poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), generally used as organic hole transport layer. Promising candidates are p-type transparent conductive oxides, which combine good optoelectronic and a higher mechanical and chemical stability than the organic counterpart. In this work, we synthesize Cu-rich CuCrO2 thin films by aerosol-assisted chemical vapour deposition as an efficient alternative to PEDOT:PSS. The effect of stoichiometry on the structural, electrical, and optical properties was analysed to find a good compromise between transparency, resistivity, and energy bands alignment, to maximize the photovoltaic performances., Average transmittance and bandgap are reduced when increasing the Cu content in these out of stoichiometry CuCrO2 films. The lowest electrical resistivity is found for samples synthesized from a solution composition in the 60–70% range. The optimal starting solution composition was found at 65% of Cu cationic ratio corresponding to a singular point in Hackee’s figure of merit of 1 × 10−7 Ω−1. PBDD4T-2F:PC70BM organic solar cells were fabricated by integrating CuCrO2 films grown from a solution composition ranging between 40% to 100% of Cu as hole transport layers. The solar cells integrating a film grown with a Cu solution composition of 65% achieved a power conversion efficiency as high as 3.1%, representing the best trade-off of the optoelectronic properties among the studied candidates. Additionally, despite the efficiencies achieved from CuCrO2-based organic solar cells are still inferior to the PEDOT:PSS counterpart, we demonstrated a significant enhancement of the lifetime in atmospheric conditions of optimal oxides-based organic photovoltaic devices.

Preparation of Poly O-Toluidine/Titanium Dioxide by In situ Chemical Oxidation Polymerization and Application for Solar Cell.

Various treatments on the PEDOT:PSS films were carried out to investigate it’s influence on the conductivity, morphology, transmittance and the corresponding impact of the performance of the organic photovoltaic devices based on the PCPDTBT:PCBM and P3HT:PCBM blends. These processing including doping PEDOT:PSS with DMF and ME solvents and exposing these films to the vapor of DMF and ME solvents, separately. A considerable enhancement of the conductivity and transmittance of PEDOT:PSS was observed after doping solvent into the PEDOT;PSS solution followed by solvent treatment through exposing these films to solvents environment. The best organic PV doped devices based on either PCPDTBT:PCBM or based on P3HT:PCBM with power conversion efficiency were 2.93% compared to 1.87% for the pristine PV devices or 2.79% compared to 1.77% for the pristine devices, respectively. The conductivity improvement was highly influenced by solvent treatment.