8.0% efficient all-polymer solar cells with high photovoltage of 1.1 V and internal quantum efficiency near unity

In very recent years, growing efforts have been devoted to the development of all-polymer solar cells (all-PSCs). One of the advantages of all-PSCs over the fullerene-based PSCs is the versatile design of both donor and acceptor polymers which allows the optimization of energy levels to maximize the open-circuit voltage (V_oc). However, there is no successful example of all-PSCs with both high V_oc over 1 V and high power conversion efficiency (PCE) up to 8% reported so far. In this work, a combination of a donor polymer poly[4,8-bis(5-(2-octylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-(5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione)-1,3-diyl] (PBDTS-TPD) with a low-lying highest occupied molecular orbital level and an acceptor polymer poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-thiophene-2,5-diyl] (PNDI-T) with a high-lying lowest unoccupied molecular orbital level is used, realizing high-performance all-PSCs with simultaneously high V_oc of 1.1 V and high PCE of 8.0%, and surpassing the performance of the corresponding PC₇₁BM-based PSCs. The PBDTS-TPD:PNDI-T all-PSCs achieve a maximum internal quantum efficiency of 95% at 450 nm, which reveals that almost all the absorbed photons can be converted into free charges and collected by electrodes. This work demonstrates the advantages of all-PSCs by incorporating proper donor and acceptor polymers to boost both V_oc and PCEs.