Dark current in a transimpedance amplifier circuit
Your first mistake is using a 741 because it is extremely poor for these types of circuits. The next problem is that you appear to be using a supply of 23 volts for the 741 with the negative supply pin connected to circuit 0 volts. The link above tells you that your inputs cannot be close to either supply rail so if you are using this circuit: -



Then it's not going to work because the input common-mode voltage range does not include the negative power pin of the 741.


  what is the mistake I am making?



Using a 741 (a dinosaur) when clearly the document you linked shows an OPA320 biased correctly for single supply operation (page one of that document).
Running a crappy op-amp from a single power supply rail and expecting things to work when the input is at 0 volts.