Oligomeric Carbazole Phosphonic Acid as Hole‐Transporting Layer for Organic Solar Cells With Efficiency of 19.63%

Abstract A class of self‐assembly monolayers, distinguished by a carbazole‐conjugated backbone pendant with phosphonic acid (PA) side units, are widely used as hole‐transporting layers (HTL) in organic solar cells (OSCs). However, challenges such as pronounced aggregation tendency and low conductivity have hindered their widespread applications. This study addresses these limitations by introducing novel oligomeric PA designs to overcome the drawbacks associated with monolayer HTLs. The newly synthesized oligomer integrates carbazole backbones and PA side units through Suzuki polymerization, showing absorption characteristics similar to small molecules, but with reduced aggregation and improved hole transport properties. OSCs using such a HTL achieve an impressive efficiency of 19.63% with remarkable stability. These results highlight the potential of oligomeric HTLs as promising materials for realizing efficient OSCs.