Enhanced performance of polymer solar cells by employing a ternary cascade energy structure

We present a route to successfully tackle the two main limitations, low open circuit voltage (V-oc) and limited short circuit-density (J(sc)), of polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) as an electron-donor. The indene-C60 bisadduct (ICBA) was selected as an electron acceptor to improve the open circuit voltage (V-oc). The narrow band gap polymer poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b: 4,5-b']dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b] thiophene)-2,6-diyl] (PBDTTT-C), as a complementary electrondonor material, was doped into the host system of P3HT: ICBA to form ternary cascade energy structured PSCs with increased Jsc. The power conversion efficiency (PCE) of P3HT: ICBA-based cells was improved from 3.32% to 4.38% by doping with 3 wt% PBDTTT-C with 1 min 150 degrees C annealing treatment. The 4.38% PCE of ternary PSCs is still larger than the 3.79% PCE of PSCs based on P3HT: ICBA with 10 minutes 150 degrees C annealing treatment.