15.9% organic tandem solar cell with extended near-infrared absorption

Abstract

Stacking single-junction organic solar cells is effective in increasing the power conversion efficiency (PCE) by reducing the thermalization loss and increasing the open circuit voltage. Recent developments of non-fullerene acceptors (NFAs) offer a range of materials whose energy gaps are suited for absorbing relatively narrow slices of the solar spectrum, thus easing requirements for current balance between sub-elements in multijunction stacks. Here, we demonstrate a solution-processed tandem organic solar cell comprising a binary, visible-absorbing sub-cell and a ternary near-infrared (NIR) absorbing sub-cell. The ternary NIR sub-cell utilizes a narrow energy gap NFA that enables a broadened and increased absorption compared to a binary NIR sub-cell. An isopropanol surface treatment is developed to connect the hydrophilic–hydrophobic surfaces in the charge recombination zone (CRZ) located between the sub-cells. The nearly optically and electrically lossless CRZ combined with an anti-reflection coating results in tandem organic photovoltaics with PCE = 15.9% ± 0.2% under AM 1.5G simulated illumination.