Performance and Durability of Polymer Solar Cells by Low-Temperature Drying Process and HfO2 Blocking Layer
Date Issued
2010
Date
2010
Author(s)
Lin, En-Yung
Abstract
This study realizes improvements in the efficiency and stability of bulk-heterojunction polymer solar cells using two approaches: morphological manipulation of the active layer composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM), and elimination of the adverse effects caused by the out-diffusion of the indium tinoxide (ITO) anode.
In terms of morphological manipulation, we developed a low-temperature drying process for the active layer that achieved significantly higher power conversion efficiency (PCE) (4.3%) and longer device lifetime (> 1250 h) than those of the standard room-temperature process. The improvements were attributed to the enhanced nucleation of the P3HT crystallites and the restricted large-scale aggregation of the P3HT/PCBM phases at the low drying temperature, which produced a densely interconnected P3HT crystal network that maximized the bulk-heterojunction area and prevented the active layer from morphological shifts with use.
In terms of diffusion blocking, we demonstrated that an ultra-thin (0.9 nm) layer of HfO2 deposited by atomic layer deposition (ALD) on the ITO anode effectively eliminated the degradation caused by the out-diffusion of In ions from the anode, while it also improved the PCE of the solar cells. The effectiveness of the ALD HfO2 blocking layer was owing to the excellent surface coverage and low defect density of the ALD films, and the improvement in PCE was due to the raised electrical field by inserted HfO2.
Subjects
polymer solar cells
degradation
low-temperature drying-process
atomic layer deposition
hafnium oxide
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