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Organic (P3HT/PCBM) solar cells are coated with ZnO nanowires as antireflection coatings and show up to 36% enhancement in efficiency. The improvement is ascribed to an effective refractive index which results in Fabry-Perot absorption bands which match the polymer band-gap. The effect is particularly pronounced at high light incidence angles. Simultaneously, the coating is used as a UV-barrier, demonstrating a 50% reduction in the rate of degradation of the polymers under accelerated lifetime testing. The coating also allows the surface of the solar cell to self-clean via two distinct routes. On one hand, photocatalytic degradation of organic material on ZnO is enhanced by the high surface area of the nanowires and quantified by dye degradation measurements. On the other, the surface of the nanowires can be functionalized to tune the water contact angle from superhydrophilic (16°) to superhydrophobic (152°), resulting in self-cleaning via the Lotus effect. The multifunctional ZnO nanowires are grown by a low cost, low temperature hydrothermal method, compatible with process limitations of organic solar cells.

Energy scavenging has become a fundamental part of ubiquitous sensor networks. Of all the scavenging technologies, solar has the highest power density available. However, the energy source is erratic. Integrating energy conversion and storage devices is a viable route to obtain self-powered electronic systems which have long-term maintenance-free operation. In this work, we demonstrate an integrated-power-sheet, consisting of a string of series connected organic photovoltaic cells (OPCs) and graphene supercapacitors on a single substrate, using graphene as a common platform. This results in lighter and more flexible power packs. Graphene is used in different forms and qualities for different functions. Chemical vapor deposition grown high quality graphene is used as a transparent conductor, while solution exfoliated graphene pastes are used as supercapacitor electrodes. Solution-based coating techniques are used to deposit the separate components onto a single substrate, making the process compatible with roll-to-roll manufacture. Eight series connected OPCs based on poly(3-hexylthiophene)(P3HT):phenyl-C61-butyric acid methyl ester (PC60 BM) bulk-heterojunction cells with aluminum electrodes, resulting in a ≈5 V open-circuit voltage, provide the energy harvesting capability. Supercapacitors based on graphene ink with ≈2.5 mF cm(-2) capacitance provide the energy storage capability. The integrated-power-sheet with photovoltaic (PV) energy harvesting and storage functions had a mass of 0.35 g plus the substrate.

We report on the improvement of power conversion efficiency (PCE) of PTB7/PC70BM solar cells by the addition of small quantities (0.02%–0.04%) of pristine single-walled carbon nanotubes (SWNTs) in the active-layer. SWNTs and purified semiconducting SWNTs (S-SWNTs) were added in quantities, which is 2 orders of magnitude lower than previously reported value and resulted in a reduction in the series resistance of the solar cell with minor changes on the shunt resistance. On addition of purified S-SWNT, the PCE of air measured devices enhanced by 29% from 4.9% to 6.3%, with short-circuit current density (Jsc) improving from 12.1 mA/cm2 to 14.4 mA/cm2 and a fill factor improvement from 54% to 61%. In addition, the role of processing additive N-Methyl-2-pyrrolidone, which acts as a SWNT dispersant, is also investigated. A single diode model of a solar cell is used to extract the cell parameters and understand the effect of SWNTs. Based on experimental data and it's fitting to the single diode model, we propose...