Achieving 18.29% efficiency of layer-by-layer all polymer solar cells enabled by iridium complex as energy donor and crystallizing agent

Series of layer-by-layer all polymer solar cells (LbL-APSCs) were constructed based on PBQx-TCl as donor and PY-DT as acceptor. Iridium complex [Ir(iqbt)₂(fprpz)] with strong photoluminescence emission and highly crystalline properties was incorporated into PY-DT and PBQx-TCl layers, resulting in power conversion efficiency (PCE) increment from 17.31 % to 18.29 %. The main contributions of the appropriate incorporation of [Ir(iqbt)₂(fprpz)] on performance improvement of LbL-APSCs can be summarized as the following: i) acting as energy donor to transfer its energy to PY-DT for prolonged exciton lifetime, resulting in enlarged exciton diffusion distance for more efficient exciton dissociation; ii) serving as crystallizing agent to prompt molecular crystallinity for achieving more effective charge transport in active layer. Meanwhile, the interfacial energy between PBQx-TCl and PY-DT layers can be increased with the incorporation of [Ir(iqbt)₂(fprpz)], which is beneficial to form more ideal vertical phase separation for efficient charge collection. The short circuit current density and fill factor of LbL-APSCs can be simultaneously improved to 25.06 mA cm⁻² and 75.75 % enabled by appropriate [Ir(iqbt)₂(fprpz)] incorporation, delivering over 5.6 % PCE improvement of LbL-APSCs. This work indicates that incorporating organometallic complex materials should be a promising strategy to push performance improvement of LbL-APSCs.