Realizing high-performance organic solar cells through precise control of HOMO driving force based on ternary alloy strategy

Abstract

A good deal of studies have proven that effective exciton dissociation and fast hole transport can operate efficiently in non-fullerene organic photovoltaics (OPVs) despite nearly zero driving force. Even so, whether such a phenomenon is universal and how small the driving force can realize the best photovoltaic performance still require a thorough understanding. Herein, despite the zero driving force based on PM6:F8IC system, a maximum short-circuit current (Jsc) of 23.0 mA/cm2 and high power conversion efficiency (PCE) of 12.2% can still be achieved. Due to the continuously adjustable energy levels can be realized in organic semiconducting alloys including F8IC:IT-4F and F8IC: Y6, the suitable third components can play the role of energy level regulator. Therefore, the HOMO energy level offset (ΔEHOMO(D‑A)) from zero to 0.07 and 0.06 eV is accomplished in the optimized IT-4F and Y6 ternary devices. Consequently, both ternary devices achieved substantially increased PCE of 13.8% and Jsc of 24.4 and 25.2 mA/cm2, respectively. Besides, pseudo-planar heterojunction (PPHJ) devices based on alloyed acceptors through sequential spin-coating method further improve the photovoltaic performance. Our work puts forward the concept of energy level regulator and prove that the ternary alloy strategy has unique advantages and huge research potential in continuously adjusting the driving force.