Converting Short circuit solar cell (5v to 50mA)
The transimpedance amplifier does invert the voltage, but if you bias the circuit you could get it to output positive values. I don't know what your current (mA) range is, but this can be calculated so that for all input values in mA can be converted to a positive voltage on the output.

Example circuit:



In this circuit you bias the positive input with a voltage. To ensure that the input current dynamic range maps to the output voltage dynamic range you have to select correct feedback resistor and voltage to the positive input.

EDIT:

Here is a simulation of a circuit using LTSpice that I did. Here a sine wave with 40 mA peak-to-peak is mapped to about 0 to 4.8 V: