We present the largest area survey to date (1.4 deg(2)) for Ly alpha emitters (LAEs) at z similar to 9, as part of the Hi-z Emission Line Survey (HiZELS). The survey, which primarily targets H' emitters at z <3, uses the Wide Field Camera on the United Kingdom Infrared Telescope and a custom narrowband filter in the J band to reach a Ly alpha luminosity limit of similar to 10(43.8) erg s(-1) over a co-moving volume of 1.12 x 10(6) Mpc(3) at z = 8.96 +/- 0.06. Two candidates were found out of 1,517 line emitters, but those were rejected as LAEs after follow-up observations. This improves the limit on the space density of bright Ly' emitters by three orders of magnitude and is consistent with suppression of the bright end of the Ly' luminosity function beyond z similar to 6. Combined with upper limits from smaller but deeper surveys, this rules out some of the most extreme models for high-redshift Ly alpha emitters. The potential contamination of narrowband Ly' surveys at z > 7 by Galactic brown dwarf stars is also examined, leading to the conclusion that such contamination may well be significant for searches at 7.7 <z <8.0, 9.1<z<9.5 and 11.7<z<12.2.