Reinforcing the Built‐In Field for Efficient Charge Collection in Polymer Solar Cells

The collection efficiency of photogenerated charges in polymer solar cells (PSCs) is strongly influenced by the built‐in field ( E in ) that develops across the photoactive materials. Here, by investigating the E in ‐development regimes in PSCs by introducing two types of interlayers, electric dipole layers (EDLs) and charge transport layers (CTLs), the device architecture is optimized to result in a larger E in . By incorporating a pair of EDLs on both sides of the photoactive layer, the E in is modulated by shifting the vacuum energy at each metal–semiconductor interface, providing a larger E in than that in conventional PSCs using typical CTLs, such as metal oxides and/or conducting polymers. These devices using paired EDLs exhibit an average PCE of 9.8%, which far surpasses the average PCE of ≈8.5% for paired CTLs.