Santos, J. D., et al. "Cause of the fill factor loss of a-Si: H p–i–n devices with ZnO: Al front electrode: Blocking contact vs. defect density." Thin solid films 548 (2013): 617-622.
You may find the following research article suitable for your query :
"Impact of absorber layer thickness, defect density, and operating temperature on the performance of MAPbI3 solar cells based on ZnO electron transporting material" by TouriaOuslimane et al.