title: Sulfide nanocrystal inks for dense Cu(In1-xGa(x))(S1-ySe(y))2 absorber films and their photovoltaic performance.
abstract: Recent developments in the colloidal synthesis of high quality nanocrystals have opened up new routes for the fabrication of low-cost efficient photovoltaic devices. Previously, we demonstrated the utility of CuInSe(2) nanocrystals in the fabrication of CuInSe(2) thin film solar cells. In those devices, sintering the nanocrystal film yields a relatively dense CuInSe(2) film with some void space inclusions. Here, we present a general approach toward eliminating void space in sintered nanocrystal films by utilizing reactions that yield a controlled volume expansion of the film. This is demonstrated by first synthesizing a nanocrystal ink composed of Cu(In(1-x)Ga(x))S(2) (CIGS). After nanocrystal film formation, the nanocrystals are exposed to selenium vapor during which most of the sulfur is replaced by selenium. Full replacement produces a approximately 14.6% volume expansion and reproducibly leads to good dense device-quality CIGSSe absorber films with reduced inclusion of void space. Solar cells made using the CIGSSe absorber films fabricated by this method showed a power conversion efficiency of 4.76% (5.55% based on the active nonshadowed area) under standard AM1.5 illumination.
authors.affiliation: School of Chemical Engineering and the Energy Center, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Qijie
authors.initials: Q
authors.lastname: Guo
authors.forename: Grayson M
authors.initials: GM
authors.lastname: Ford
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Hillhouse
authors.forename: Rakesh
authors.initials: R
authors.lastname: Agrawal