Layered All-Polymer Solar Cells with Efficiency of 18.34% by Employing Alloyed Polymer Donors

A series of layered all-polymer solar cells (LA-PSCs) with the normal or inverted structure are prepared by employing a sequential spin-coating method with PBQx-TCl, PM1 as polymer donor, and PY-DT as polymer acceptor. The power conversion efficiency (PCE) of normal LA-PSCs can be improved from 17.20% to 18.34% by incorporating 30 wt.% PM1 into the PBQx-TCl layer, resulting from simultaneously increased J_SC of 25.35 mA cm^-2, V_OC of 0.971 V and FF of 74.49%. The PCE improvement of inverted LA-PSCs can also be achieved by employing PBQx-TCl:PM1 as donor layers. The mixed PBQx-TCl and PM1 prefer to form the alloyed states in the LA-PSCs, which can be confirmed by the gradually increased V_OCs of LA-PSCs with more PM1 content in donor layers. Meanwhile, the photogenerated excitons in donor layers can also be dissociated at the interface between PBQx-TCl and PM1, especially for the excitons located near the ITO electrode. The exciton dissociation between PBQx-TCl and PM1 can provide an additional channel for improving the exciton utilization efficiency, as confirmed by the positive external quantum efficiency spectral difference (∆EQE) values for the normal and inverted LA-PSCs with PBQx-TCl:PM1 or PBQx-TCl as donor layers. Over 6.6% PCE improvement of LA-PSCs can be realized by using alloyed PBQx-TCl:PM1 as the donor layer.