Low-concentration doping of spiro-OMeTAD using a multifunctional solubilization agent for stable perovskite solar cells

Chemical doping is essential for spiro-OMeTAD when acting as a hole transport layer in efficient perovskite solar cells (PSCs). However, the hygroscopic and volatile nature of conventional LiTFSI/tBP dopants accelerates device degradation under environmental stresses. To address this issue, a low-concentration dopant system has been constructed using the multifunctional additive triallyl isocyanurate (TAIC), in which the molar ratio of LiTFSI/tBP/TAIC is 1:1:1. TAIC features three isocyanurate groups (-N-C=O) that strongly coordinate with Li + ions, significantly improving the solubility of LiTFSI in chlorobenzene without requiring acetonitrile. Compared to the conventional LiTFSI/tBP doping system (1:6 M ratio), TAIC promotes the formation of spiro-OMeTAD· + radicals while suppresses the aggregation and phase separation of lithium salts in the spiro-OMeTAD film. Furthermore, interactions between the isocyanurate groups in TAIC effectively passivate perovskite defects. Consequently, carbon-based PSCs employing TAIC-modified spiro-OMeTAD achieves an enhanced efficiency of 20.63 %, outperforming 18.87 % of the control. Silver-based PSCs fabricated using TAIC-modified spiro-OMeTAD exhibits a maximum PCE of 24.21 %, whereas the control group yields only 22.85 %. Moreover, Non-encapsulated TAIC-modified devices retains 92 % of their initial PCE after 1512 h at 70 % relative humidity. This work significantly alleviates stability challenges in spiro-OMeTAD hole transport layer, thereby simultaneously improving the efficiency and stability of PSCs.