Electrical engineering

Nanotechnology

Photovoltaics

Organic solar cell

Engineering

Composite material

Materials science

Photovoltaic system

Photoactive layer

Optoelectronics

Polymer

Nature Energy

The performance of organic photovoltaics is largely dependent on the balance of short-circuit current density (JSC) and open-circuit voltage (VOC). For instance, the reduction of the active materials’ optical bandgap, which increases the JSC, would inevitably lead to a concomitant reduction in VOC. Here, we demonstrate that careful tuning of the chemical structure of photoactive materials can enhance both JSC and VOC simultaneously. Non-fullerene organic photovoltaics based on a well-matched materials combination exhibit a certified high power conversion efficiency of 12.25% on a device area of 1 cm2. By combining Fourier-transform photocurrent spectroscopy and electroluminescence, we show the existence of a low but non-negligible charge transfer state as the possible origin of VOC loss. This study highlights that the reduction of the bandgap to improve the efficiency requires a careful materials design to minimize non-radiative VOC losses. Materials design rules play a key role in enabling high performance in organic photovoltaics. Here the authors achieve 12.25% efficiency on 1 cm2 non-fullerene solar cells by tuning the side chains’ branching point and the fluorine substitutions in donor and acceptor materials.

Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics