It will be hard to answer correctly without knowing the details of your system. However, these are my suggestions.

1. Check your parameters with more literatures. Sometimes parameters differ from paper to paper depending on the other materials used.

2. Add recombination coefficients properly.

3. Use proper absorption files.

4. Add defects and/or interfacial defects if necessary.

5. Otherwise, try using different ETL/HTL layers. If you get optimized value then change your parameters accordingly.