Why are we even interested in solar cells under bias voltage? I couldn't find any answer on this super basic question.
Some people on the internet say that you would not put a solar cell in an array under bias, others say that they bias themselves, but I don't understand how this would work: In a series circuit a solar cell would be biased by the adjacent solar cell, right? And it would be a reverse bias, correct? (Since + and - meet.) But then there is also a paper saying that reverse bias is detrimental, or is it meant in a way that there is a "healthy" reverse bias (normal working condition) and a "pathological" reverse-bias (shunt resistances --> hot spots) ?
Please help me understand this, I am getting really desperate over this and can't find anyone who knows something about it.
 A: Solar cells are photovoltaic devices: they develop a photo-voltage when illuminated. In this sense they bias themselves. But that is a very confusing way of thinking about the as components in an electrical circuit.
To get useful power out of a solar cell you must apply forward bias. The optimum bias is at the maximum power point (peak of the dashed curve).
The IV curve (solar black line) of an illuminated diode enters three (two shown in the diagram) quadrants:

*

*Negative current, negative (reverse) voltage: photodetector

*Positive current, positive (forward) voltage: solar cell

*Negative current, positive (forward) voltage: light emitting diode

For more background on this read this site, https://www.pveducation.org/pvcdrom/solar-cell-operation/iv-curve
The same principle applies when the solar cells are interconnected in a solar module. There will be additional current and voltage matching constraints depending on how the module is interconnected, but the shape of the IV curve will still retain this fundamental feature of three quadrants.
I recommend you answer your own question by playing around with a very simple SPICE model of a single solar cell. Then make it more complicated by connecting multiple devices in series and then in parallel and see how the IV curve changes.
