Is there a voltage buck converter which also boosts output current?
I measure by shorting the converter with the multimeter. So to measure input current/voltage, with the whole circuit connected:I place multimeter black on in-, multimeter red on in+. For output current/voltage: multimeter black on out-, multimeter red on in+ (shorting the battery)


This means you are not measuring the current that the solar cell is delivering to the switching converter. You are short circuiting the cell with the ammeter, and measuring what the cell can provide into a short circuit.

Then you short circuit the converter output and measure what it can provide into a short circuit. The way a buck converter works, when you short its output, it will essentially just short its input to its output. And again you will measure what the cell can drive into a short circuit.

Like Peter Bennett says in comments, in order to know what the currents in and out of the converter are in the operating circuit, you must break the circuit and insert the ammeter between the cell and the converter input; then insert the meter between the converter and the load.