Organic photovoltaic cells (OPVs) have the potential of becoming a productive renewable energy technology if the requirements of low cost, high efficiency and prolonged lifetime are simultaneously fulfilled. So far, the remaining unfulfilled promise of this technology is its inadequate operational lifetime. Here, we demonstrate that the instability of NFA solar cells arises primarily from chemical changes at organic/inorganic interfaces bounding the bulk heterojunction active region. Encapsulated devices stabilized by additional protective buffer layers as well as the integration of a simple solution processed ultraviolet filtering layer, maintain 94% of their initial efficiency under simulated, 1 sun intensity, AM1.5 G irradiation for 1900 hours at 55 °C. Accelerated aging is also induced by exposure of light illumination intensities up to 27 suns, and operation temperatures as high as 65 °C. An extrapolated intrinsic lifetime of > 5.6 × 104 h is obtained, which is equivalent to 30 years outdoor exposure.
Ternary blend organic
photovoltaics (OPVs) have been introduced
to improve solar spectral absorption and reduce energy losses beyond
that of binary blend OPVs, but the difficulties in simultaneously
optimizing the morphology of three molecular components result in
devices that have generally exhibited performance inferior to that
of analogous binary OPVs. Here, we introduce a small molecule-based
biternary OPV comprising two individual, vacuum-deposited binary bulk
heterojunctions fused at a planar junction without component intermixing.
In contrast to previous reports where the open circuit voltage (V
OC) of a conventional, blended ternary cell
lies between those of the individual binaries, the V
OC of the biternary OPV corresponds to one of the constituent
binaries, depending on the order in which they are stacked relative
to the anode. Additionally, dipole-induced energy-level realignment
between the two binary segments necessary to achieve maximum efficiency
is observed only when using donor–acceptor–acceptor′
dipolar donors in the photoactive heterojunctions. The optimized biternary
OPV shows improved performance as compared to its two constituent
binary OPVs, achieving a power conversion efficiency of 10.6 ±
0.3% under AM 1.5G 1 sun (100 mW/cm2) simulated illumination
with V
OC = 0.94 ± 0.01 V, a short
circuit current density of 16.0 ± 0.5 mA cm–2, and a fill factor of 0.70 ± 0.01.
Semi-transparent organic photovoltaics (ST-OPVs) have the potential for integration with windows for ubiquitous power generating applications. Typically, such applications require that ST-OPVs be neutrally transparent across the visible and exhibit both a high average photopic transmittance (APT) and color rendering index, as well as iso-energetic chromaticity coordinates. In this work, we demonstrate the design and use of optical coatings to achieve ST-OPVs with a neutral visible transmittance of APT = 50%, a power conversion efficiency of 8.3%, and optical properties that are independent of a ± 30° variation in the solar angle of incidence. These simple optical coatings are rapidly designed using a genetic algorithm and transfer matrix formalism.
Equipping buildings with energy harvesting windows is a practical way to reduce greenhouse gas (GhG) emission. Utilizing semi-transparent organic photovoltaics (ST-OPVs) for this application requires the device to be colorfast, allowing for no change in the aesthetics or light harvesting property of the window. Here, we demonstrate an ST-OPV that is colorfast under 1 Sun AM 1.5G illumination at 50 0 C and relative humidity of 34 %.
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