Crystallinity and phase separation induced morphological modulation for efficient ternary all-polymer solar cells

Abstract

All-polymer solar cells (all-PSCs) have attracted enormous attention and achieved significant progress in recent years due to their long-term stability and excellent film stretchability. However, the problem of morphology control in bulk-heterojunction (BHJ) films due to highly entangled polymeric chains hinders the further improvement of device performance. In this work, we obtained fine-tuned photoactive layer morphology through reconstructed microstructure induced by steric effects to realize an improved device performance in ternary all-PSCs. The large tetrahexylphenyl substituents on the backbone of naphthalene diimide–indacenodithienothiophene based copolymer acceptor BL-102 bring forth the steric-hindrance effect and influence intermolecular interactions. Therefore, the copolymer BL-102 delivers the property of suppressed self-aggregation, causing reconstructed crystalline features and morphology in blending films. The ternary devices tended to reduce the excessive phase separation by suppressing the aggregation of original polymers but to promote intermixing behaviors. Therefore, the optimal BHJ film manifested a well-formed bi-continuous interpenetrating nanoscale network with a larger π–π stacking coherence length and ordered face-on molecular orientation. Hence, a faster electron transfer (ET) and hole transfer (HT) process combined with balanced charge carrier mobilities can be achieved to enhance the overall device performance. This work provides an effective method to regulate the photoactive layer morphology of all-PSCs through structurally steric hindrance effects and demonstrate the significance of ternary-blending strategy induced nanoscale morphology modulation for fabricating highly efficient all-PSCs.