Trap states, electric fields, and phase segregation in mixed-halide perovskite photovoltaic devices

Journal article

Mixed-halide perovskites are essential for use in all-perovskite or perovskite–silicon tandem solar cells due to their tunable bandgap. However, trap states and halide segregation currently present the two main challenges for efficient mixed-halide perovskite technologies. Here photoluminescence techniques are used to study trap states and halide segregation in full mixed-halide perovskite photovoltaic devices. This work identifies three distinct defect species in the perovskite material: a charged, mobile defect that traps charge-carriers in the perovskite, a charge-neutral defect that induces halide segregation, and a charged, mobile defect that screens the perovskite from external electric fields. These three defects are proposed to be MA+ interstitials, crystal distortions, and halide vacancies and/or interstitials, respectively. Finally, external quantum efficiency measurements show that photoexcited charge-carriers can be extracted from the iodide-rich low-bandgap regions of the phase-segregated perovskite formed under illumination, suggesting the existence of charge-carrier percolation pathways through grain boundaries where phase-segregation may occur.

Authors: Knight, AJ; Patel, JB; Snaith, HJ; Johnston, MB; Herz, LM

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Wiley
• Journal: Advanced Energy Materials
• Volume: 10
• Issue: 9
• Article number: 1903488
• Publication date: 2020-01-30
• DOI: 10.1002/aenm.201903488
• EISSN: 1614-6840
• ISSN: 1614-6832
• Language: English
• Keywords: electric fields; perovskites; photovoltaic devices; FFR; trap states; halide segregation