Trainable solar cell effect in TPPS4 nanowires

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Title: Trainable solar cell effect in TPPS4 nanowires
Author: Van Aken, Katherine L.
Advisor: Smith, Walter F.
Department: Haverford College. Dept. of Physics
Type: Thesis (B.S.)
Issue Date: 2012
Abstract: The photovoltaic currents have been measured for self-assembled meso-tetra(4-sulfonatophenyl) porphine (TPPS4) nanowires. This is surprising, given that these devices are symmetrical. However, by “training” the nanowires with a bias voltage, the symmetry can be broken. After training, when the nanowires are illuminated with a 488 nm laser under zero bias voltage, a solar cell current is observed, with polarity opposite to the training voltage. The magnitude of solar cell current depends on both the time of training and the magnitude of the training voltage. After the training voltage is removed, the solar cell current decays very quickly initially and then transitions to a much slower decay. This suggests that there are different populations of trapped charges that are repositioned by the electric field of the training voltage and that are responsible for the solar cell current. Experiments under vacuum suggest that these trapped charges are adsorbed oxygen molecules. A qualitative model is presented in which the Schottky barriers at the interfaces with electrodes are affected by these trapped charges, leading to asymmetrical charge transport and thus to the observed current.
Subject: Nanowires -- Electric properties
Subject: Solar cells -- Electric properties
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Van Aken, Katherine L.. "Trainable solar cell effect in TPPS4 nanowires". 2012. Available electronically from

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