Mobility usually depends on the microstructure and grain size (if carrier scattering in grain boundaries is important). The mobility in mono-crystals could be much bigger than in poly-crystals with nanometric size grains. Annealing for re-crystallization could increase grain-size and hence improve mobility.

any other parameters mean?

I mean solar cell related all parameters i.e. carriers concentration, band gap, lattice vectors etc.

extrinsic parameters such as cooling may help.

Mobility usually depends on the microstructure and grain size (if carrier scattering in grain boundaries is important). The mobility in mono-crystals could be much bigger than in poly-crystals with nanometric size grains. Annealing for re-crystallization could increase grain-size and hence improve mobility.

For solar cells application choice of material depends on the band gap which should be around 1.5 eV  and absorption coefficient high, lifetime of carriers high ,I.e., defect density low and molity high. Mobility depends upon the material used. If you select material of high mobility, you may not be satisfying other conditions. There is slight increase in mobility with decrease in temperature but for solar cell applications it is not viable as one uses solar cells at room temperature.Mobility in amorphous silicon is much smaller than crystalline silicon but amorphous silicon solar cells are being used for commercial cells because of low pay back period. I suggest to make solar cells of low payback period without worrying mobility.

First you should ask: is the mobility that I measure comparable to the literature values for this material?

If the answer is yes then there is not a lot that you can do without changing materials. Strain can help increase the mobility in some cases; if the films are so thin that their thickness is comparable to the mean free path of the carriers, then increasing their thickness can improve the mobility dramatically.

If the mobility that you measure is considerably lower than what is reported in the literature then the problem is your films. First I'd consider impurities, non-stoichiometries and defects. If this is a single crystalline, epitaxial film, then you should estimate the degree of crystallinity (XRD: bragg peaks and rocking curves for start). If this is a poly-crystalline films then grain boundaries can have a considerable effect on the mobility as well.

If you could specify the material, substrate, deposition method, mobility values and how they were measured - it would be easier to give you a more detailed response.

Basically, scattering centres need to be reduced to increase the carrier mobility. Decreasing impurity content in the thin film will improve mobility. Larger grain size will also help. Surface roughness may be another factor.  

The conductivity of a semiconducting material, in addition to being dependent on electron and/or hole concentrations, is also a function of the charge carriers’ mobilities, that is, the ease with which electrons and holes are transported through the crystal. Furthermore, magnitudes of electron and hole mobilities are influenced by the presence of those same crystalline defects that are responsible for the scattering of electrons in metals—thermal vibrations (i.e., temperature) and impurity atoms. Influence of dopant, at dopant concentrations less than about 10 20 m-3, both carrier mobilities are at their maximum levels and independent of the doping concentration. In addition, both mobilities decrease with increasing impurity content. For dopant concentrations of 10 24 m-3 and below, both electron and hole mobilities decrease in magnitude with rising temperature; again, this effect is due to enhanced thermal scattering of the carriers. For both electrons and holes, and dopant levels less than 1020 m -3, the dependence of mobility on temperature is independent of acceptor/donor concentration.

how does electron & hole mobilities differ when determined using Hall method. what are the factors that differentiate electron & hole mobilities