Solar cell is a electrical device that converts the energy of light directly into electricity. The ones that that calculators used are called photovoltaic cells. The word "photovoltaic" is really easy to memorize: "photo" means light, while "voltaic" means electricity. Since calculators doesn't need much energy, one photovoltaic cell is suffucient to power it. But for solar phone chargers, satellites, emergency road signs, they need more power and so multiple photovoltaic cells are linked together to make the voltage higher, just like we use two alkaline batteries in some toys that requires 3 volt (1 alkaline battery produces roughly 1.5v), while we use 4 alkaline batteries (6v) in remote toy helicopters. Human nowadays just can't live without silicon. Our computer CPUs are made of silicon, and so does the solar cells. But solar cells can be made with other semi-conductors that have similar properties like silicon. In simple terms, this is how solar cell procudes electricity: When sun light shines on the the surface of a solar cell, light is absorbed into the semi-conductor, then the light energy knocks electrons loose, so they can move around the circuit and produces a current that can power our electrical equipment.
However, the truth is more complicated. After electrons are knocked loose, they still won't flow in the same direction on their own and form a unique current. In order to fix this, Solar cells have some electric field build-in functions that can make all of these loose electrons to flow in one direction, so they can form a current. And like normal batteries, two metal plates / contacts is attached to two sides of the solar cell so the current can be lead into the circuit and flow in the circuit and hense power up the electrical equipment.