Integrated organic donor-acceptor bulk heterojunctions for self-activated liquid crystal light modulators.

Optically addressed spatial light modulators (OASLM) are promising for holographic applications and optical limiters. Self-activated OASLMs can operate as autonomous energy devices, opening the route to stand-alone laser protection devices and smart windows. They are mainly based on liquid crystal (LC) devices, integrated with inorganic photovoltaic substrates such as LiNbO₃:Fe or dye-sensitized TiO₂. While robust, they also suffer from several restrictions such as high costs, low performances and/or small device area. In this work, we propose a new type of an autonomous modulator. Blends of electron-donating (D) conjugated polymers and electron-accepting (A) fullerene molecules were used as a photovoltaic thin films and integrated into liquid crystal device. Such D/A bulk heterojunctions are the major building block of solution-processed organic solar cells and are known to convert incident light into electrical energy. In our case, the organic layer generates a photovoltaic field that is used to control the LC alignment under illumination. We carried out cross-polarized intensity measurements on this photovoltaic-LC device to demonstrate the expected occurrence of a light–dependent birefringence change, without an applied voltage. In this way, by combining solution-processed organic photovoltaic thin films with optical responsive liquid crystals, our work paves the way to low cost and large area self-sustained optical devices.