13.2% Efficiency of Organic Solar Cells by Controlling Interfacial Resistance Resulting from Well-Distributed Vertical Phase Separation

Abstract

Two strategies were investigated to improve the efficiency of organic solar cells (OSCs) with the aim of controlling the interfacial resistance in the devices: the use of a ternary active layer and the introduction of conjugated polymers. The ternary active layer was formed by introducing PC 71 BM between a high-performance non-fullerene photoactive material P(Cl−Cl) (BDD = 0.2) and the IT-4F-based binary active layer, thereby reducing the interfacial resistance between the donor and acceptor via vertical phase separation. Furthermore, the introduction of the conjugated polymer PFN-Br created a well-dispersed separation attributable to enhancement of the interfacial contact with the active layer and simultaneous reduction of the interfacial resistance. Consequently, the synergetic effect of the ternary active layer and PFN-Br enhanced the short-circuit current density (J SC ) and fill factor (FF) to realize a power conversion efficiency (PCE) of 13.2%.

Nonhalogenated Solvent‐Processed Thick‐Film Ternary Nonfullerene Organic Solar Cells with Power Conversion Efficiency >13% Enabled by a New Wide‐Bandgap Polymer

“…Atomic force microscopy (AFM) was performed to study the surface morphologies of the binary and ternary NFOSCs. [ 59 ] The height images (Figure 5b) show that the binary and ternary NFOSCs were different in this regard. The root mean square (RMS) values for P2:IT‐4F, P2:IT‐4F:BTP‐4F, and P2:IT‐4F:BTP‐4Cl were 2.05, 2.0, and 0.76 nm, respectively.…”

“…The structures of the thick‐film NFOSCs were analyzed by grazing‐incidence X‐ray diffraction (GIXRD). [ 59–61 ] Figure a–d show 2D GIXRD images and corresponding in‐plane and out‐of‐plane 1D profiles extracted along the q xy and q z directions, respectively. As shown in Figure 6a, P1 and P2 are amorphous, whereas the NFAs are highly crystalline, which is consistent with the DSC measurements.…”

“…Figure 6e, Figure S18, Supporting Information, show the molecular behaviors for different thick active layers analyzed by cross‐sectional field‐emission scanning electron microscopy (FE‐SEM) and energy‐dispersive X‐ray spectroscopy (EDS) mapping. [ 59 ] The distributions of donors and NFAs were identified by EDS mapping. Images of Si, O, Cl, F, and S atomic signals were acquired, as shown in Figure 1.…”

Ink Engineering of Transport Layers for 9.5% Efficient All‐Printed Semitransparent Nonfullerene Solar Cells

“…In the normal configuration, the addition of CN resulted in a similar behavior, as the improved nanomorphology increased the J sc 23.1–26.5 mA cm −2 . These devices demonstrated higher series resistance values (5.46 Ω) in comparison with devices in inverted configuration, perhaps coming from an unfavorable vertical stratification profile, [ 52–54 ] resulting in slightly lower FF values at 61.1%. Nonetheless, the overall performance was elevated from 8.2% with a CB ink to 11.8% with a CB:CN ink.…”

Electric‐Induced Degradation of Cathode Interface Layer in PM7:IT‐4F Polymer Solar Cells

“…PFN‐Br is a commonly used cathode buffer layer material for the feature of excellent electronic transmission performance, enhancement of the interfacial contact, reduction of the interfacial resistance, and so on. [ 28–30 ] PFN‐Br improves the power conversion efficiency (PCE) of PM7:IT4F OSCs obviously from 4.35% to 9.77%. However, the PFN‐Br‐modified OSCs exhibit obvious degradation once the devices undergo electrical measurement such as applying bias voltage onto the device for current density–voltage ( J–V ) test, the subsequent photovoltaic performance exhibits significant degradation.…”