Amorphous Film Technology
Imagine if a PV cell was made with a microscopically thin deposit of silicon, instead of a thick wafer. It would use very little of the precious material. Now, imagine if it was deposited on a sheet of metal or glass, without the wasteful work of slicing wafers with a saw. Imagine the individual cells deposited next to each other, instead of being mechanically assembled. That is the idea behind thin film technology. (It is also called amorphous, meaning "not crystalline".) The active material may be silicon, or it may be a more exotic material such as cadmium telluride.
Thin film panels can be made flexible and light weight by using plastic glazing. Some flexible panels can tolerate a bullet hole without failing. Some of them perform slightly better than crystalline modules under low light conditions. They are also less susceptible to power loss from partial shading of a module.
The disadvantages of thin film technology are lower efficiency and uncertain durability. Lower efficiency means that more space and mounting hardware is required to produce the same power output. Thin film materials tend to be less stable than crystalline, causing degradation over time. The technology is being greatly improved however, so we do not wish to generalize here. We will be seeing many new thin film products introduced in the coming years, with efficiency and warranties that may approach those of crystalline silicon.
PV experts generally agree that crystalline silicon will remain the "premium" technology for critical applications in remote areas. Thin film will be strong in the "consumer" market where price is a critical factor. As usual, you get what you pay for.