Energy Level Alignment in Ternary Organic Solar Cells. (23rd June 2020)

• Record Type: Journal Article
• Authors: Lami, Vincent; Hofstetter, Yvonne J.; Butscher, Julian F.; Vaynzof, Yana
• Is Part Of: Advanced Electronic Materials. Volume 6:Number 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-23
• Subjects: open‐circuit voltage -- ternary organic photovoltaics -- UPS depth profiling; Materials -- Electric properties -- Periodicals; Materials science -- Periodicals; Magnetic materials -- Periodicals; Electronic apparatus and appliances -- Periodicals; 537
• DOI: 10.1002/aelm.202000213
• Languages: English
• ISSNs: 2199-160X

Abstract

Abstract: Ternary organic solar cells (TOSC) are currently under intensive investigation, recently reaching a record efficiency of 17.1%. The origin of the device open‐circuit voltage (VOC), already a multifaceted issue in binary OSC, is even more complex in TOSCs. Herein, two ternary systems are investigated with one donor (D) and two acceptor materials (A1, A2) including fullerene and nonfullerene acceptors. By varying the ratio between the two acceptors, VOC is found to be gradually tuned between those of the two binary systems, D:A1 and D:A2. To investigate the origin of this change, ultraviolet photoemission spectroscopy (UPS) depth profiling is employed, which is used to estimate the photovoltaic gap in the ternary systems. The results reveal an excellent agreement between the estimated photovoltaic gap and the VOC for all mixing ratios, suggesting that the energetic alignment between the blend components varies depending on the ratio D:A1:A2. Furthermore, the results indicate that the sum of radiative and nonradiative losses in these ternary systems is independent of the blend composition. Finally, the superiority of UPS over X‐ray photoemission spectroscopy (XPS) depth profiling is demonstrated in resolving compositional profiles for material combinations with very similar chemical, but dissimilar electronic structures, as common in TOSCs. Abstract : The alignment of energy levels in ternary organic photovoltaic blends is studied using ultraviolet photoemission spectroscopy depth profiling. The photovoltaic gaps extracted from the measured ternary blend energetics are in excellent agreement with the device open‐circuit voltages at different blend ratios, suggesting that the sum of radiative and nonradiative losses in these ternary systems is independent of the blend composition.