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The photo-degradation of polymer solar cells is a critical challenge preventing its commercial deployment. We experimentally fabricate organic solar cells and characterize their degradation under solar simulators in an environmental chamber under nitrogen flow, without exposure to oxygen and moisture. We have developed a thermally stable inverted organic solar cell architecture in which light induced degradation of device characteristics can be reversibly annealed to the pristine values. The stable inverted cells utilized MoO x layers that are thermally treated immediately after their deposition on the organic layer, and before metal cathode deposition. Organic solar cells that are photo-degraded in the presence of oxygen, however show irreversible degradation that cannot be thermally recovered. The decrease of organic solar cell characteristics correlates with increases in mid-gap electronic states, measured using capacitance spectroscopy and dark current. It is likely the photo-induced defect states caused by local H motion from the alkyl chains to the aromatic backbone, can be reversibly annealed at elevated temperatures after photo-degradation. Our results provide a pathway for improving the stability of organic photovoltaics. [ABSTRACT FROM AUTHOR]

We design, simulate and fabricate enhanced thin film silicon solar cells using periodically textured photonic crystal substrates. We utilize a thin film absorber layer consisting of a superlattice of alternating hydrogenated amorphous silicon (a-Si:H) and nano-crystalline silicon (nc-Si). Rigorous vectorial simulations optimized the periodically patterned solar cells by solving Maxwell?s equations in Fourier space. Simulations found optimized architectures for a triangular lattice of metallic nano-cones as a back-reflector, and a conformal solar cell geometry. The periodically patterned photonic crystal based substrates achieve (1) high diffraction, enhancing the path length of light in thin absorber layers and (2) plasmonic concentration of light intensity. Simulations predict an absorption enhancement of 43% for a 12-period superlattice of 800 nm thickness. The optimized pitch of the photonic lattice is near 700 nm. Experimentally the periodically patterned substrates were fabricated with nano-imprint lithography, and utilized as a substrate for the superlattice cells. We measured a large photo-current enhancement between the textured photonic crystal based superlattice cell and the flat cell of 21%, together with long-wavelength quantum efficiency enhancements beyond 600 nm. This is an approach to achieving thin film solar cells with high currents through advanced light-trapping techniques on novel materials. [ABSTRACT FROM AUTHOR]