Microscopic Mechanism of High Efficiency and Stability of Inverted Polymer Fullerene Solar Cells

Abstract

The performance of organic solar cells has been remarkably improved recently, where the cell structures are important for achieving high efficiency and stability. The formation and accumulation of long-lived charges in the cells are critical for the efficiency and stability of the cells; however, their relations with the cell structures have not yet been clarified from a microscopic viewpoint. Here, we report the microscopic mechanism of high efficiency and stability of inverted polymer fullerene solar cells compared to conventional cells even though the same photoactive layers are utilized. We directly observe the formation and accumulation of long-lived charges in these cells with electron spin resonance at a molecular level. We find the reduced effects of the formation and accumulation of long-lived charges in the inverted cells on their efficiency and stability compared to the case of conventional cells. These findings provide a striking advance in fundamental understanding, which is useful for further clarifying the operation mechanism of organic solar cells as well as further improving their efficiency and stability.

Open-Circuit-Voltage Improvement Mechanism of Perovskite Solar Cells Revealed by Operando Spin Observation

“…For this study, we performed ESR spectroscopy, which has been used successfully to examine organic and perovskite solar cells and related materials, − particularly to elucidate the effects of electron transfer and trapping near PEDOT:PSS/CH 3 NH 3 PbI 3 interfaces on device performance. This study takes advantage of the feature that ESR spectroscopy can separate the effect of charge transfer between PEDOT:PSS/CH 3 NH 3 PbI 3 from other factors, for example, including ion migration and the number of defect states of perovskite layers.…”

Effects of the Addition of Tin Powder to Perovskite Precursor Solutions on Band Bending at PEDOT:PSS/Perovskite Interfaces in Mixed-Cation Mixed-Halide Tin Perovskite Solar Cells

“…For this study, we investigate the effects of Sn powder addition to the perovskite precursor solution on band bending at poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) HTL/perovskite interfaces in FA 1– x MA x Sn­(I 1– y Br y ) 3 PSCs, using electron spin resonance (ESR) spectroscopy, which has successfully applied for perovskite solar cells and materials − and for organic thin film solar cells. − In studies on PSCs, ESR spectroscopy has been used to nondestructively and easily characterize the formation of space-charge regions and band bending at buried interfaces in stacked film samples and complete devices. ,, ESR measurements indicated that FA 0.75 MA 0.25 Sn­(I 0.75 Br 0.25 ) 3 shows significant downward band bending near PEDOT:PSS, leading to reduced hole selectivity and enhanced surface recombination. On the other hand, FA 0.75 MA 0.25 Sn­(I 0.75 Br 0.25 ) 3 with Sn powder was found to exhibit upward band bending near PEDOT:PSS owing to reduced Sn 4+ concentration.…”