We report on the fabrication and photovoltaic characteristics of InGaN solar cells by exploiting InGaN/GaN multiple quantum wells (MQWs) with In contents exceeding 0.3, attempting to alleviate to a certain degree the phase separation issue and demonstrate solar cell operation at wavelengths longer than previous attainments (>420 nm). The fabricated solar cells based on In0.3Ga0.7N/GaN MQWs exhibit an open circuit voltage of about 2 V, fill factor of about 60%, and an external efficiency of 40% (10%) at 420 nm (450 nm).
The effect of thermal annealing treatment on the morphology change in bulk heterojunction (BHJ) in organic photovoltaic cells was studied by photoemission spectroscopy. The results reveal that vertical phase separation upon annealing occurs in typical BHJ layer formed between planar molecule CuPc and spherical C60 with inhomogeneous concentration distribution in profile, varying from CuPc-rich near the air surface to C60-rich adjacent to the substrate interface. The morphology variation is associated with the difference in surface energy of CuPc and C60, leading to the accumulation of CuPc to the interface with air to lower the overall energy of the free surface.
Enhanced performance of a poly͑3-hexylthiophene͒:͑6,6͒-phenyl C 61 butyric acid methyl ester bulk heterojunction polymer photovoltaic cell is reported by modifying the indium tin oxide ͑ITO͒ anode with chloroform solution. Instead of the traditional UV-ozone treatment, the optimized chloroform modification on ITO anode can result in an enhancement in the power conversion efficiency of an identical device, originating from an increase in the photocurrent with negligible change in the open-circuit voltage. The performance enhancement is attributed to the work function modification of the ITO substrate through the surface incorporation of the chlorine, and thus improved charge collection efficiency.
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