| Summary: | Abstract All‐polymer solar cells (All‐PSCs) have attracted tremendous research interest in the recent decade due to the great potentials in stretchable electronic applications in terms of long‐term stability and mechanical stretchability. Driven by the molecular design of novel polymer acceptors and morphology optimization, the power conversion efficiency (PCE) of All‐PSCs has developed rapidly and now exceeded 17%. This review outlines the promising strategies for high‐performance All‐PSCs from the aspect of morphology control with the motivation to rationally guide the optimization. In this review, we briefly discuss the thermodynamic mixing principles of all‐polymer blends and the effects of the molecular structure of conjugated polymers on thin‐film morphology in All‐PSCs. The crucial role of molecular miscibility in influencing morphological features and performance metrics was highlighted. We also expound on the effective methods of controlling film morphology through properly tuning the aggregation behavior of polymers. In particular, insightful studies on the commonly used naphthalene diimide‐based acceptor polymers and the newly emerging polymerized nonfullerene small molecule acceptors (ITIC‐series, Y6 ‐series, etc) are discussed in detail. Finally, we present an outlook on the major challenges and the new opportunities of All‐PSCs for efficiency breakthroughs targeting 20%.
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