Root-Cause Failure Analysis of Photocurrent Loss in XXXX : @entity16820 -Based Inverted Solar Cells.

@entity27416 @entity16820 @entity71361 @entity34687 @entity1948
UNASSIGNED: Metal oxide transport layers have played a crucial role in recent progress in organic photovoltaic (OPV) device stability. Here, we measure the stability of inverted and encapsulated @entity27416 : @entity16820 cells with @entity34687 /Ag/Al composite anode in operational conditions combining solar radiation and 65   C. Performance loss of over 50% in the first 100 h of the aging is dominated by a drop in the short-circuit current (Jsc). We reveal a concurrent loss in reflectance from 85% to 50% above 650 nm, which is below the optical gap of the used photoactive materials, hence, excluding any major degradation in the bulk of this layer. Correlating the responses of aged devices to a series of test structures comprised of ITO/ @entity1948 cathode, @entity34687 /Ag, and @entity34687 /Ag/Al anodes and their combinations with the active layer allowed us to identify that the presence of Al causes the reduced reflectance in these devices, independent of the presence of the active layer. Systematic single-stress aging on the test structures further indicates that elevated heat is the cause of the reflectance loss. Cross-section transmission electron microscopy coupled with elemental analysis revealed the unsuspected role of Al; notably, it diffuses through the entire 150 nm thick Ag layer and accumulates at the @entity34687 /Ag interface. Moreover, XRD analysis of the aged @entity34687 /Ag/Al anode indicates the formation of Ag2Al alloy. Depth profiling with X-ray photoelectron spectroscopy advanced our understanding by confirming the formation of Ag-Al intermetallic alloy and the presence of oxidized Al only at the @entity34687 /Ag interface suggesting a concomitant reduction of @entity34687 to most probably @entity71361 . This latter compound is less reflective than @entity34687 , which can explain the reduced reflectance in aged devices as proven by optical simulations. On the basis of these results, we could estimate that 20% of the loss in Jsc is ascribed to reduction of @entity34687 triggered by its direct contact with Al.
