  We study the properties of photochemical hazes in super-Earths/mini-Neptunes
atmospheres with particular focus on GJ1214b. We evaluate photochemical haze
properties at different metallicities between solar and 10000$\times$solar.
Within the four orders of magnitude change in metallicity, we find that the
haze precursor mass fluxes change only by a factor of $\sim$3. This small
diversity occurs with a non-monotonic manner among the different metallicity
cases, reflecting the interaction of the main atmospheric gases with the
radiation field. Comparison with relative haze yields at different
metallicities from laboratory experiments reveals a qualitative similarity with
our theoretical calculations and highlights the contributions of different gas
precursors. Our haze simulations demonstrate that higher metallicity results
into smaller average particle sizes. Metallicities at and above
100$\times$solar with haze formation yields of $\sim$10$\%$ provide enough haze
opacity to satisfy transit observation at visible wavelengths and obscure
sufficiently the H$_2$O molecular absorption features between 1.1 $\mu$m and
1.7 $\mu$m. However, only the highest metallicity case considered
(10000$\times$solar) brings the simulated spectra into closer agreement with
transit depths at 3.6 $\mu$m and 4.5 $\mu$m indicating a high contribution of
CO/CO$_2$ in GJ1214b's atmosphere. We also evaluate the impact of aggregate
growth in our simulations, in contrast to spherical growth, and find that the
two growth modes provide similar transit signatures (for D$_f$=2), but with
different particle size distributions. Finally, we conclude that the simulated
haze particles should have major implications for the atmospheric thermal
structure and for the properties of condensation clouds.
