(a) Enlarged drawing of the anode, cathode, and sandwich structure of single cell with area of . (b) Illustration of the interdigitated organic solar cell array consisted of 20 single cells. The bottom (light purple) layer is photolithography-defined ITO anode, the middle (red) layer is spin-coated P3HT:PCBM, and the top (light blue) layer is thermal deposited cathode by shallow mask technique.
The fabrication process of miniature solar cell array. Start from (1) a clean ITO on glass substrate, followed by (2) spin-coating photoresistance, (3) development of desired pattern by photolithography, (4) etching off the unwanted ITO, (5) washing off the photoresistance, (6) spin-coating active layer (P3HT:PCBM), (7) clean off excessive material, (8) deposit cathode via shadow mask.
Upper panel: schematic of a single organic solar cell with bulk heterojunction structure. Lower panel: current-voltage characteristics of single cell made with P3HT:PCBM mixed with weight ratio of 1:1 under simulated AM1.5G, radiation at . The active layer was spun-coat on patterned ITO substrate at , with a final thickness of about . Post-device thermal annealing at for was done before the measurements.
(a) A digital picture of the organic solar array with 20 miniature cells in series, (b) current-voltage curve of an organic solar array with nine functioning cells measured at simulated AM1.5G with radiation of . The fabrication parameters are the same as single cell (in Fig. 3). The inset shows array as a function of number of cells in series. An output voltage of was achieved with 18 cells in series.
Summary of device parameters for three organic solar cell arrays containing different numbers of cells in series. The current voltage characteristics in dark and under simulated solar AM1.5 with an intensity of are present. Each cell has an active area of . The power conversion efficiency was calculated using Eq. (2) in text.
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