Modifications to tungsten trioxide sol processing for improved solar energy conversion efficiency

摘要

An H_2WO_(4(aq))-based sol processing route has been developed to allow the ink jet printing of photocatalytically active WO_3 films. The effect of different heat treatment atmospheres and the addition of triethanolamine upon the structure, composition, optical properties and IPCE response of films printed upon conducting glass substrates (ITO) have been studied using x-ray diffraction, Raman microscopy, UV-visible spectroscopy and photocurrent spectroscopy. It has been discovered that heat treatment under a nitrogen atmosphere inhibits formation of a well defined crystal structure but may extend the tail of the IPCE response curve into the visible range as far as 700 nm. Likewise, the presence of triethanolamine in the precursor sol tends to disrupt the WO_3 crystallization process leading to the formation of amorphous material and residual organic material in the heat treated film. However, UV-visible spectroscopy of these films indicates optical absorption similar to that of crystalline WO_3 except with increased absorption in the visible region from 350 nm to 600 nm. These observations are supported by ab initio calculations predicting that the incorporation of nitrogen into the monoclinic WO_3 lattice leads to band gap narrowing and the introduction of mid-gap states.