Efficient polymer:fullerene bulk heterojunction solar cells with n-type doped titanium oxide as an electron transport layer

We have reported a highly n-type doped solution-processed titanium metal oxide (TiOx) for use as an efficient electron-transport layer (ETL) in polymer:fullerene bulk heterojunction (BHJ) solar cells. When the metal ions (Ti) in TiOx are partially substituted by niobium (Nb), the charge carrier density increased, by an order of magnitude, because of the large electronegativity of Nb compared to that of Ti. Therefore, the work function (WF) of Nb-doped metal oxide (Nb-TiOx) decreases from 4.75 eV (TiOx) to 4.66 eV (Nb-TiOx), leading to an enhancement in the power conversion efficiency (PCE) of BHJ solar cells with a Nb-TiOx ETL (from 7.99% to 8.40%).