The manufacturing shift to China can account for a one-time step decrease in solar PV costs due to lower wages and a lower cost, dirtier industrial ecosystem (e.g. high-CO2 grid power supplied mostly by coal plants having minimal pollution controls).
But the costs of solar panels made in China in 2020 are much lower than those of solar panels made in China in 2010. Chinese factory wages have not fallen over the past 10 years, nor have Chinese pollution controls been further relaxed. The trend of falling costs over the last 10 years of made-in-China solar panels is due to improved techniques of production.
In 2010, Chinese producer Suntech was the largest PV manufacturer in the world. It sold 1.6 GW of panels and realized revenue of $2.9 billion:
https://www.greentechmedia.com/articles/read/suntech-q4-earn...
Its panels were therefore selling for about $1.83 per watt in 2010.
Presently, Chinese high efficiency monocrystalline PERC panels are selling for no more than $0.25 per watt:
http://pvinsights.com/
This 85% drop in prices indicates that technological and manufacturing progress in the solar sector continued at a rapid clip even after its center of gravity shifted to China.