Performance enhancement of small molecular solar cells via luminescent sensitizer 4,5-bis(carbazol-9-yl)-1,2- dicyanobenzene (2CzPN)

Enhanced performance of small molecule organic solar cells is presented by incorporating a blue luminescent sensitizer layer 4,5-bis(carbazol-9-yl) -1,2-dicyanobenzene (2CzPN). As a result, 68% enhancement of power conversion efficiency is achieved from 1.54% (without sensitizer 2CzPN) to 2.60% (with 3 nm 2CzPN). The improvement is attributed to the increase of photocurrent and open-circuit voltage (V-OC) because of subphthalocyanine (SubPc) reabsorption of photon from the emission of 2CzPN. The absorption spectrum of 2CzPN is complementary with the donor SubPc, and its photoluminescence spectrum overlaps with the absorption spectrum of the active layer. The V-OC increases from 0.98 V to 1.17 V due to the slightly deeper highest occupied molecular orbital level of 2CzPN than SubPc. The estimated hole injection barrier slightly increases from 0.809 eV (without 2CzPN) to 0.874 eV (with 5 nm 2CzPN) and the hole mobility simultaneously decreases. This strategy provides a facile approach for effective utilization of high-energy photons.