Small Molecule, Polymer and Perovskite Photovoltaic Cells with Very High Performance
Yang Yang a b
a Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States
b California NanoSystems Institute, University of California, Los Angeles, California 90095, United States
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Invited Speaker, Yang Yang, presentation 235
Publication date: 1st March 2014

Solution-processed organic solar cells and organic-inorganic hybrid solar cells are among the most promising photovoltaic technologies for eventuallow-cost manufacture. In this presentation, I will briefly report our recent work towards realizing the potential of small molecule, polymer and perovskite photovoltaics.

(1) Small molecule OPV.  Small molecule organic semiconductors have attracted increasing interest due to the advantages of its well-defined structures, facile synthesis and purification, and generally high charge carrier mobility. In the first part of my presentation, I will report high performance single junction and double junction OPV device based on DOR3T-BDTT. Using the solution spin-coating fabrication process, the certified power conversion efficiency (PCE) of 8.02% from single junction device was obtained. A homo-tandem solar cell was constructed with a novel solution processed interlayer (or tunnel junction), demonstrating an unprecedented PCE of 10.1%.

(2) The second part of my presentation is on polymer solar cells. Recently, we demonstrated two families of NIR conjugated polymers (Eg ~ 1.4 eV) specifically suitable for the tandem structure. One is based on alternating benzodithiophene/diketopyrrolopyrrole units and the other is based on alternating dithienopyran/diflourobenzothiadiazole units. In the single-layer devices, power conversion efficiencies (PCE) of 7~8% were achieved. When the polymers were applied to tandem solar cells, we demonstrated PCE of 10.6% (under the AM 1.5G solar condition). Furthermore, the tandem devices show excellent stability due both to the intrinsic stability of the polymer and the advanced device structure.

(3) The third part of my presentation is on the organic-inorganic hybrid perovskite based solar cells, particularly CH3NH3PbX3 (X=Cl, Br, I). We demonstrate a novel low temperature vapor assisted solution process to fabricate organic-inorganic hybrid perovskite films (e.g. CH3NH3PbX3, X=Cl, Br, I) and the corresponding photovoltaic devices. The perovskite films derived from this approach exhibit superior film quality, with full surface coverage, uniform grain structure with grain sizes up to the micron scale, and a complete precursor transformation. Facilitated by the excellent film quality, the CH3NH3PbI3 materials enable a PCE over 12% in a planar architecture.  We have further improved device engineering, and our latest perovksite solar cell has reached efficiencies in the range of 15-18%*. We believe that further research in film formation, device architecture, and interface engineering will lead to further improvement of perovskite solar cell devices.

*Un-certified results.  Certification is underway.

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