Manipulating the solubility properties of polymer donors for high-performance layer-by-layer processed organic solar cells

High-performance polymer donors are highly demanded to fulfil the potential of layer-by-layer (LBL) processed organic solar cells (OSCs). In this study, we present an effective method to develop high-performance polymer donors for LBL-OSCs by manipulating their solubility properties. The solubility of naphthalenothiophene imide (NTI)-based polymers could be easily manipulated by employing linear or branched alkyl chains in NTI. The polymer PNTB6-Cl with linear alkyl chains insoluble in chloroform could tolerate the chloroform processing by washing away the polymers only in the amorphous region, resulting in an LBL film with a much smoother surface and more efficient photoluminescence quenching, while chloroform-soluble polymer PNTB-Cl did not. PNTB6-Cl:N3 based LBL devices exhibited an efficiency of 17.59%, much higher than 15.24% for PNTB-Cl:N3 based devices and 16.20% for control devices based on PM6:N3. Importantly, the excellent batch-to-batch reproducibility of PNTB6-Cl overcomes the notorious batch-dependent issue in polymer donors, indicating that PNTB6-Cl is a promising polymer donor for LBL-OSCs. Our studies demonstrate that the solubility property of a polymer could significantly impact electron acceptor penetration, phase separation and photovoltaic performance of LBL-OSCs, which provide the guidelines for high-performance polymer donor design.