Two-step templating strategy enabled 20.70% efficiency in layer-by-layer organic solar cells

Abstract

The uncontrollable diffusion dynamics of the top layer of layer-by-layer organic solar cells (LBL OSCs) often lead to undesirable phase-separation morphology, limiting their photovoltaic performance. Herein, we present an innovative, two-step templating (TST) strategy to systematically regulate the stacking behavior of bottom layer and deposition dynamics of top layer to optimize the active-layer morphology. The first step (plasticing strategy) employed a designed polymer plasticizer, PBTP-BDD, to modulate the chain stacking behavior of D18, which created a primed template that prolonged the deposition dynamics of L8-BO and promoted its ordered self-assembly, achieving a power conversion efficiency (PCE) of 19.95%. In the second step (rinsing strategy), chloroform solvent was used to selectively rinse the plasticized layer, which reconstructed this initial template into a thermodynamically stable and structurally ordered state, guiding L8-BO to adopt a more favorable crystal orientation and further boosting the PCE to 20.70%; this PCE was significantly superior to those of the control devices (18.53%) and rinsing-only devices (18.94%), demonstrating the notable advantages of the TST strategy. Moreover, the TST strategy exhibited exceptional generality, thus achieving an excellent PCE of 18.08% in 300 nm thick-film OSCs. This work provides an important foundation and process guidance for the fabrication of high-performance LBL OSCs through the synergistic regulation of deposition dynamics.