Role of PbSe Structural Stabilization in Photovoltaic Cells

2015-02-11
Asil Alptekin, Demet
Walker, Brian J.
Ehrler, Bruno
Vaynzof, Yana
Sepe, Alessandro
Bayliss, Sam
Sadhanala, Aditya
Chow, Philip C. Y.
Hopkinson, Paul E.
Steiner, Ullrich
Greenham, Neil C.
Friend, Richard H.
Semiconductor nanocrystals are promising materials for printed optoelectronic devices, but their high surface areas are susceptible to forming defects that hinder charge carrier transport. Furthermore, correlation of chalcogenide nanocrystal (NC) material properties with solar cell operation is not straightforward due to the disorder often induced into NC films during processing. Here, an improvement in long-range ordering of PbSe NCs symmetry that results from halide surface passivation is described, and the effects on chemical, optical, and photovoltaic device properties are investigated. Notably, this passivation method leads to a nanometer-scale rearrangement of PbSe NCs during ligand exchange, improving the long-range ordering of nanocrystal symmetry entirely with inorganic surface chemistry. Solar cells constructed with a variety of architectures show varying improvement and suggest that triplet formation and ionization, rather than carrier transport, is the limiting factor in singlet fission solar cells. Compared to existing protocols, our synthesis leads to PbSe nanocrystals with surface-bound chloride ions, reduced sub-bandgap absorption and robust materials and devices that retain performance characteristics many hours longer than their unpassivated counterparts.