Recent research on co solutions for the growth of SiC single crystals by HTSG method through various methods is represented. The research scope of solvents involves thermal physical performance parameters, C dissolution, thermochemical properties, thermodynamic properties, and other aspects. However, the existing research has not yet identified the optimal solubilizing system from a theoretical perspective, as well as the substantial impact of element ratios in various solution systems on crystal growth. There are still several difficulties in the research of solutions as follows:

1) It is difficult to test the mixed solution due to the high experimental temperature of the HTSG method. At present, it is possible to roughly predict the thermal and physical performance parameters of solutions through theoretical calculations, but equipment for the related experiments is unavailable and the cost is also high. Effectively improving the accuracy of simulation and conducing accurate predictions for experiments can be achieved via in-depth research on the changes in thermal and physical performance parameters of solutions.

2) The concentration of C in the solution is a key factor affecting the quality of crystal growth. The concentration of C is investigated both theoretically and experimentally under ideal conditions of thermal equilibrium. The seed crystals can experience melt-through during the remelting process of crystal growth, if the concentration of C in the solution is too low. On the contrary, if the concentration of C in the solution is too high, it is likely that crystallization can occur before the impurities on the surface of the seed crystal are completely melted. The situations above could seriously affect the quality of the crystal growth. It plays an important role in improving crystal quality via in-situ detecting the changes in C concentration inside the crucible.

3) The existing HTSG method usually uses graphite crucibles as a C source for crystal growth. As the temperature inside the crucible increases, graphite crucible is continuously corroded by the solution, presenting different shapes. Different shaped crucibles can seriously affect the stability of the flow field inside the crucible, and even change the trajectory of the flow field. In-depth research on the corrosion process of graphite crucibles by auxiliary solutions can effectively avoid negative effects caused by changes in flow field and temperature field in the later stage of growth.

Although there are still some difficulties to overcome in the study of solvents for the growth of SiC single crystals by the HTSG method with the continuous efforts of numerous research teams, some key issues are constantly proposed and solved. The research on solvents can also accelerate the pace of HTSG method for growing SiC single crystals, opening a door to low-cost and low-energy SiC single crystal growth.