Design and development of plasmonic nanostructured electrodes for ITO-free organic photovoltaic cells on rigid and highly flexible substrates.

Indium tin oxide (ITO) is the most common transparent electrode used in organic photovoltaics (OPVs), yet limited indium reserves and poor mechanical properties make it non-ideal for large-scale OPV production. To replace ITO, we designed, fabricated, and deployed plasmonic nanostructured electrodes in inverted OPV devices. We found that active layer absorption is significantly impacted by ZnO thickness which affects the optical field distribution inside the resonant cavity formed between the plasmonic nanostructured electrode and top electrode. High quality Cr/Au nanostructured electrodes were fabricated by nanoimprint lithography and deployed in ITO-free inverted devices on glass. Devices with thinner ZnO showed a PCE as high as 5.70% and higher J SC's than devices on thicker ZnO, in agreement with finite-difference time-domain simulations. In addition, as the active layer was made optically thin, ITO-based devices showed diminished J SC while the resonant cavity effect from plasmonic nanostructured electrodes retained J SC. Preliminary ITO-free, flexible devices on PET showed a PCE of 1.82% and those fabricated on ultrathin and conformable Parylene substrates yielded an initial PCE over 1%. The plasmonic electrodes and device designs in this work show promise for developing highly functioning conformable devices that can be applied to numerous needs for lightweight, ubiquitous power generation.

Solvent-molecule-mediated manipulation of crystalline grains for efficient planar binary lead and tin triiodide perovskite solar cells.

Binary lead and tin perovskites offer the benefits of narrower band gaps for broader adsorption of solar spectrum and better charge transport for higher photocurrent density. Here, we report the growth of large, smooth crystalline grains of bianry lead and tin triiodide perovskite films via a two-step solution process with thermal plus solvent vapor-assisted thermal annealing. The crystalline SnxPb1-xI2 films formed in the first step served as the templates for the formation of crystalline CH3NH3SnxPb1-xI3 films during the second step interdiffusion of methylammonium iodide (MAI). Followed by dimethylsulfoxide (DMSO) vapor-assisted thermal annealing, small, faceted perovskite grains grew into large, smooth grains via the possible mechanism involving bond breaking and reforming mediated by DMSO solvent molecules. The absorption onset was extended to 950 and 1010 nm for the CH3NH3SnxPb1-xI3 perovskites with x = 0.1 and 0.25, respectively. The highest PCE of 10.25% was achieved from the planar perovskite solar cell with the CH3NH3Sn0.1Pb0.9I3 layer prepared via the thermal plus DMSO vapor-assisted thermal annealing. This research provides a way to control and manipulate film morphology, grain size, and especially the distribution of metal cations in binary metal perovskite layers, which opens an avenue to grow perovskite materials with desired properties to enhance device performance.

Inverted hybrid CdSe-polymer solar cells adopting PEDOT:PSS/MoO3 as dual hole transport layers.

Inverted CdSe quantum dots (QDs):poly (3-hexylthiophene) (P3HT) organic/inorganic hybrid solar cells (OIHSCs) with the PEDOT: PSS/MoO3 dual hole transport layers (HTLs) showed superior performance over those with a single HTL of PEDOT: PSS or MoO3. The enhanced electron blocking at the active layer/anode interface as well as the prevention of leakage current accounted for the enhancement in the efficiency of the solar cells with the dual HTLs. By adopting the inverted structure and using the dual HTLs, the resistive losses of the CdSe QDs:P3HT hybrid system at high illumination power were effectively prevented. Further study showed the structure of dual HTLs was applicable to the solar cells with CdSe QDs and nanorods (NRs) blended with poly(thienothiophene-co-benzodithiophenes)7-F20 (PTB7-F20).

Controlled colloidal synthesis of iron pyrite FeS2 nanorods and quasi-cubic nanocrystal agglomerates.

Earth-abundant and nontoxic pyrite iron disulfide (FeS2) is very promising for photovoltaic applications but the phase purity and the morphology of iron pyrite nanocrystals (NCs) have a significant impact on the solar cell performance. In this work, we systematically investigated reaction conditions and the local chemical environment on the phase purity and morphology of iron pyrite NCs synthesized via the hot injection method. By using different solvents to dissolve iron and sulfur agents, varying reactant concentrations, and adding trioctylphosphine oxide (TOPO) or 1,2-hexadecanediol (Diol) into the reaction solution, iron pyrite short, branched and chromosome-like rods were obtained with a diameter of ~10 nm and a length of ~20-30 nm as well as quasi-cubic NC agglomerates with a size of ~200 nm. Our experimental results show that the molar ratio of sulfur to iron and the reaction temperature are two critical factors in determining the crystalline phase of the synthesized materials. A mechanism involving the generation of H2S is proposed to explain the phase purity observed. The as-synthesized iron pyrite NCs can be dispersed well in chloroform, chlorobenzene, toluene, and hexane and thus are promising in solution-processable photovoltaic applications.

Multilayers based on cationic nanocomplexes for co-delivery of doxorubicin and DNA.

Co-delivery of drugs and genes has synergistic advantages in many fields such as cancer treatments. In this study, we present a multilayers for co-delivery of doxorubicin (DOX) and DNA. Ferrocene-modified polyethyleneimine (PEI-Fc) is synthesized, and it can form micelles in solution with ferrocene core and PEI shell. DOX and DNA are thus incorporated into the core and shell of the micelles, respectively, to form the PEI-Fc-DOX-DNA nanocomplexes. Such cationic nanocomplexes are used to construct multilayers through layer-by-layer assembly with negatively charged dextran sulfate (DS). We show that the multilayers can release DOX, and the release can be significantly enhanced in a hydrogen peroxide condition. Moreover, the multilayers have the ability to transfect cells through a substrate-mediated mode. The (PEI-Fc-DOX-DNA/DS) multilayers can be potentially applied to the biomedical devices for cancer treatment, regenerative medicine, etc.