(262e) Photonic Curing of Nanocrystals for Photovoltaics

Nanocrystal inks are being explored as a route to low cost high efficiency photovoltaic (PV) devices. The efficiency of nanocrystal devices is limited by charge transport through the nanocrystal film and higher efficiencies can be achieved by sintering the nanocrystals into polycrystalline films.  For copper-indium-selenide (CIS), this is done by thermal annealing under a selenium rich atmosphere above 500^oC (called selenization). This processing step is relatively expensive and difficult to control. 

Therefore, we have been exploring nanocrystal film processing strategies that might alleviate this step.  Here, we present results on the use of rapid photonic curing using a rapid broadband pulsed light source to transiently heat the sample, which allows for sintering of CIS films on metallic contacts and helps prevent the outgassing of selenium from the film. We demonstrate a working solar cell fabricated from a photonically sintered CIS film. The choice of back contact material is critical for achieving working sintered devices, as the thermal conductivity and optical properties of the contact have a large impact on the film heating. We also demonstrate the removal of organic capping ligand from the film without inducing grain growth. In this case, nanocrystals come into direct contact with each other and charge transport is greatly increased. Devices made from nanocrystal films without capping ligands demonstrate high short circuit current and external quantum efficiency, although the overall device efficiency is limited due to a low open circuit voltage.