Strategies toward High Efficiency Organic and Perovskite Solar Cells
1 Department of Materials Science and Engineering and California NanoSystems Institute, University of California, Los Angeles, California 90095, United States
Abstract: In this presentation, I will report two major research topics in my group: organic photovoltaics, and perovskite solar cells. Organic solar cells have emerged as one of the future promising photovoltaic technologies because they offer the advantage of ease fabrication and cost-effective advantages. However, due to the nature of molecular orbitals, the absorption spectrum of organic semiconductors is narrow, typically around 300nm bandwidth, and as a result insufficient broad-absorption has been a major problem. Our strategy to achieve higher performances includes the use of tandem solar cell architectures by combining two (or more) cells with complementary spectral absorption ranges into a vertically stacked device, or using ternary solar cells by introducing a third material to broaden the absorption window. These approaches can ultimately lead to power conversion efficiencies (PCE) of organic solar cells reaching over 11%. In addition, we have incorporated an ultra-thin layer of the perovskite thin film as the charge transport layer, we observed a very high Voc for the bilayer PVSK/OPV device.
On the other hand, the state of the art perovskite (PVSK) solar cell has achieved a certified PCE of 22.1% using cost-effective processing methods. However, further improvements are expected to be achievable based on the superior optoelectronic properties of the PVSK materials. Recent studies have unraveled a key for achieving higher performances in manipulation of defects in the PVSK layer to realize microscopically homogeneity in PCE. In this regard, we present a novel strategy to minimize the defects by engineering of intermediate phases and interfaces. Careful modulation of intermediate phases led to growth of highly crystalline PVSK with reduced defects, in which the remaining surface and interfacial defects were passivated by a self-assembled monolayer or Lewis base additive. With the reduced defect density and enhanced carrier lifetime, PCEs exceeding 19% (steady-state PCE >18%) were achieved in. In addition, I will also report our tandem perovskite solar cell research.