Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Publication date: 1st March 2014
The soft-processing methodologies, where soft elastomeric materials are key elements for processing, have provided the opportunity to improve our understanding of organic solar cells. Specifically, we have constructed and deconstructed organic solar cells with bulk-heterojunction architecture via soft-contact lamination and delamination. The soft-contact lamination and delamination was reversible, allowing direct characterization of once-buried photoactive layer after post-treatment and device characterization. It confirmed that short-circuit current density is proportional to the crystallinity of photoactive layer. However, it was not clear the crystallinity increase was main factor to enhance short-circuit current density of organic solar cells because post-treatment such as thermal annealing affects crystallinity of constituents as well as phase separation of electron donor and electron acceptor.
To decouple phase separation from constituent crystallization in organic solar cells, we constructed plana-heterojunction solar cells with simple interface between electron donor and electron acceptor using soft-contact lamination. Generally, it is difficult to fabricate plana-heterojunction solar cells due to solvent orthogonality. So, coating electron acceptor dissolves underlying electron donor, destroying pristine interface between them. We introduced soft-contact lamination to solve this problem. Specifically, we prepared electron donor and electron acceptor on different substrates and then laminated electron donor against electron acceptor. Thermal annealing was intentionally avoided to maintain the pristine interface after lamination. In plana-heterojunction solar cells, we don’t need to take complicated phase separation into account anymore when understanding the relationship between crystallinity and device performance of organic solar cells. Also, we independently processed individual organic semiconductor layers before lamination to control the crystallinity of constituents. We found 15% change of P3HT crystallinity was not enough to affect device performance in P3HT:PCBM organic solar cell. On the contrary, thermal annealing of PCBM significantly changed device performance. Thermal annealing of PCBM in air dramatically deteriorated device performance due to oxidation of PCBM. When we annealed PCBM under N2, it initially improved device performance and then deteriorated device performance. While the improvement was attributed into crystallinity increase of PCBM, the deterioration was correlated with the development of preferential orientation of PCBM that hinders vertical electron mobility.
1. Kim, J. B.; Lee, S.;Toney, M. F.; Chen, Z.; Facchetti, A.; Kim, Y. S.; Loo, Y. –L. Reversible Soft-Contact Lamination and Delamination for Non-Invasive Fabrication and Characterization of Bulk-Heterojunction and Bilayer Organic Solar Cells. Chem. Mater. 2010, 22, 4931-4938. 2. Kim, J. B.; Guan, Z. –L.; Shu, A. L.; Kahn, A.; Loo, Y. –L. Annealing Sequence Dependent Open-Circuit Voltage of Inverted Polymer Solar Cells Attributable to Interfacial Chemical Reaction between Top Electrodes and Photoactive Layers. Langmuir 2011, 27, 11265-11271. 3. Kim, J. B.; Guan, Z. –L.; Lee, S.; Pavlopoulou, E.; Toney, M. F.; Kahn, A.; Loo, Y. –L. Modular Construction of P3HT/PCBM Planar-Heterojunction Solar Cells by Lamination Allows Elucidation of Processing-Structure-Function Relationships
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International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.
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