A two-step strategy to clarify the roles of a solution processed PFN interfacial layer in highly efficient polymer solar cells

Abstract

† Electronic Supplementary Information (ESI) available: [detailed J-V characteristic curves; the key parameters of PSCs dependence on the soaking time; the work functions of active layers]. SeeSolution processed PFN interfacial layer has been demonstrated as an efficient method to improve the performance of polymer solar cells (PSCs). The champion power conversion efficiency (PCE) of PSCs with PBT7-Th:PC 71 BM as the active layer was increased from 6.13% to 7.72% by directly spin-coating PFN methanol solution on the surface of active layers or to 8.50% for the active layer with 4 min PFN methanol solution soaking. The champion PCE of PSCs was further increased to 8.69% for the active layers with a twosteps treatment, 4 min methanol soaking and then directly spin-coating PFN methanol solution. A 12.6% PCE improvement was obtained by using the two-steps strategy compared with directly spin-coating PFN methanol solution on the active layers. The methanol soaking the active layers plays the key role in forming the more ideal vertical phase separation for efficient exciton dissociation, charge carrier transport and collection. An ultrathin PFN interfacial dipole layer can be obtained by directly spin-coating PFN methanol solution. The two-steps strategy may provide a simple and effective method to finely optimize the phase separation and obtain an ultrathin PFN interfacial dipole layer for the performance improvement of PSCs.

Molecular design of interfacial layers based on conjugated polythiophenes for polymer and hybrid solar cells

“…Water‐soluble conjugated polyfluorene electrolytes have been widely investigated as CIL materials . Poly((9,9‐bis(3′‐( N,N ‐dimethylamino)propyl)‐2,7‐fluorene)‐ alt ‐(9,9‐dioctyl‐2,7‐fluorene)) ( PFN ) is potentially the CPE most commonly used as a cathodic interlayer . For example, Sun et al observed an enhancement in PCE, from 6.13% to 7.72%, upon incorporation of a PFN cathodic IL between an active layer of PTB7‐Th : PC 71 BM (Scheme ) and an Al electrode .…”

“…Poly((9,9‐bis(3′‐( N,N ‐dimethylamino)propyl)‐2,7‐fluorene)‐ alt ‐(9,9‐dioctyl‐2,7‐fluorene)) ( PFN ) is potentially the CPE most commonly used as a cathodic interlayer . For example, Sun et al observed an enhancement in PCE, from 6.13% to 7.72%, upon incorporation of a PFN cathodic IL between an active layer of PTB7‐Th : PC 71 BM (Scheme ) and an Al electrode . The improvement was attributed to the strong interfacial dipoles formed by the thin PFN layer, which caused an enhancement in the built‐in potential across the active layer and led to efficient charge carrier transport and collection .…”

“…). These ILs perform a variety of functions, from charge collection and transport to diminishing detrimental factors such as current leakage, poor energy level alignment, charge recombination etc . This leads to remarkable improvements in the intrinsic device parameters, such as the short‐circuit current density ( J sc ), open‐circuit voltage ( V oc ) and fill factor (FF), and thus the overall PCE of the device.…”

Colorful semitransparent polymer solar cells employing a bottom periodic one-dimensional photonic crystal and a top conductive PEDOT:PSS layer

“…PFN is used as the ITO surface modifier to lower the work function and eliminate the space charge build-up and charge recombination. 29 An ohmic contact can be formed at the interface of PFN/active layer, which is advantageous to the photogenerated charge-carrier collection. 30 A blend of PTB7: [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) (1:1.5 by weight) is used as the photoactive layer with PC 71 BM as the electron acceptor.…”

Difluorobenzothiadiazole based two-dimensional conjugated polymers with triphenylamine substituted moieties as pendants for bulk heterojunction solar cells

“…The performance of a PSC is strongly dependent on the morphology of its conjugated polymer/fullerene derivative composite film [52][53][54]. To avoid recombination of excitons, the morphology of the P/N heterojunction phase must be controlled at the nanoscale level [29].…”