Small Molecule Heterojunction Solar Cells Employing Mixed Donor-Acceptor Active Regions and Buffer Layers.

Organic solar cells;Electrical Engineering;Engineering;Electrical Engineering

Xiao, XinGuo, L. Jay ;

University of Michigan

关键词: Organic solar cells;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/113608/xxiao_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Organic photovoltaic (OPV) cells are considered as a promising candidate for renewable energy sources of the next generation due to their advantages of low cost, light weight and mechanical flexibilities. This dissertation targets on the development and understanding of high efficiency and large area small molecule OPV cells with mixed donor-acceptor heterojunctions (HJ) and buffer layers.The first part of this thesis focuses on a mixed HJ OPV cell employing tetraphenyldibenzoperiflanthene (DBP) and C70 as donor and acceptor. We systematically analyze loss mechanisms inside the mixed HJ cell. A hybrid planar-mixed heterojunction (PM-HJ) structure is employed to reduce exciton quenching at the MoO3/organic interface, whereas an exciton blocking/electron conducting buffer comprised of wide energy gap molecules and C60 is implemented to suppress bimolecular recombination and exciton-polaron quenching. The optimized DBP:C70 PM-HJ cell achieves power conversion efficiency (PCE) = 8.1 ± 0.4 % under simulated AM 1.5G illumination at one sun intensity. In the second part of this thesis, we employ DBP:C70 mixed HJ as a blue-green absorbing sub-cell in the tandem paired with various near infrared(NIR)-absorbing sub-cells. A solution-processed blended functionalized squaraine/C70 bilayer HJ is employed as a NIR-absorbing sub-cell. To further enhance the absorption in NIR, we use a vacuum-deposited DTDCTB:C60 PM-HJ in the tandem, leading to PCE = 10.0 ± 0.2%. Furthermore, we develop triple and four-junction OPV cells to enable the photon harvesting at the second order interference maxima, resulting in a significant improvement in EQE and PCE. In addition, we develop inverted semitransparent OPV cells using both mixed and PM-HJ structures along with a semitransparent tandem cell.Finally, we study the scalability of OPV cells. Multi-junction OPV cells exhibit reduced loss in PCE for large area devices compared to single junction cells due to the lower current and higher voltage during operation. We further fabricate organic solar modules consisting of 25, 1 cm^2 discrete multi-junction cells connected in a series-parallel circuit configuration with a yield of 100% for discrete cells and a deviation of PCE from cell to cell of <10%.