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ECN publication
Exploring the limits of hybrid TiO2/conjugated polymer photovoltaic cells
Slooff, L.H.; Veenstra, S.C.; Kroon, J.M.; Koetse, M.M.; Sweelssen, J.
Published by: Publication date:
ECN Solar Energy 1-11-2005
ECN report number: Document type:
ECN-RX--05-030 Conference Paper
Number of pages: Full text:
8 Download PDF  

Presented at: SPIE Conference; Optics & Phonotonics, San Diego, USA, 31 juli 2005-4 augustus 2005.


In hybrid polymer photovoltaics, conjugated polymers are combined with wide bandgap metal oxide semiconductors like TiO2 or ZnO. Reported maximum power conversion efficiencies (PCE) at AM1.5G conditions for a hybrid polymer bulkheterojunction device are up to 1.6 %. In this paper we report on the current-voltage characteristics of bi-layer devices consisting of TiO2 and a conjugated polymer. Several polymers with different optical bandgap were studied. The maximum External Quantum Efficiency (EQE) of the devices is comparable, but the PCE differs considerably (0.2-0.5%). The differences can for a large part be explained by the differences in optical bandgap of the polymers. It is shown that a low band gap is beneficial for the short circuit current, but does not automatically result in a high PCE as relative shifts of the highest occupied molecular orbital (HOMO) energy levels of the polymers reduce the open circuit voltage (Voc). The calculations show that a PCE up to ~ 19 % can be achieved using the maximum possible Voc and a fill factor of 80%. Judicious engineering of material combinations is required to achieve such a power output, and it expresses the need for a continuing search on potentially low cost, efficient metal oxide/polymer BHJ tructures.

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