Optimization of Band Alignment by Organic Molecules for Perovskite Solar Cells

A methodology for optimization of band alignment in perovskite solar cells using organic molecule adsorption is investigated by using first-principles calculations. We focused on the modification of the work function after the adsorption of hole-collecting monolayer (HCM) materials bearing alkyl phosphonic acid anchoring groups on indium tin oxide (ITO), a transparent electrode substrate. The optimized structures of adsorbed HCM molecules and the ITO surface were obtained, and then the modification of the work function due to the influence of the electric double layer was determined. The calculated results show that the face-on oriented tripodal triazatruxene derivative (3PATAT-C3) has a better energy level tunability and higher stability than the edge-on oriented monopodal carbazole-based 2PACz, which is well-known as one of the representative HCM materials, and explain the advantage of 3PATAT-C3 for perovskite solar cells with a higher power conversion efficiency.