Engineering the germanium sulfide embedded carbon nanotube composites doped electron transport layer for enhanced perovskite solar cell characteristics

The commercialisation of perovskite solar cells (PSCs) hinges on addressing their inherent instability, as device performance degrades rapidly under environmental stressors such as heat, moisture, oxygen, and light. This study addresses the dual challenges of efficiency and stability by engineering a novel hybrid electron transport layer (ETL). We developed a composite of germanium sulfide (GeS) and carbon nanotubes (CNT) denoted GeS@CNT integrated into a PCBM matrix to enhance charge management and interfacial robustness. In this architecture, the CNT scaffold facilitates rapid electron transport, while GeS nanocrystals provide effective defect passivation, which is synergistically enhanced by the CNT-Ge-S bonding. Optimization yielded a champion power conversion efficiency (PCE) of 23.47%, surpassing devices with pure PCBM (21.08%) or GeS-only ETL (22.83%). The GeS@CNT ETL demonstrated exceptional operational stability. Under thermal stress (heating from 60 °C to 80 °C), the GeS@CNT-based device retained 89% of its performance, significantly outperforming the control (62%). Furthermore, after 1500 h in dark storage (30–40% RH), it retained 73% of its initial PCE, compared to 42% for the pure ETL device. Most notably, under continuous illumination, the GeS@CNT device showed minimal degradation, highlighting outstanding photostability. This work presents an effective strategy for developing multifunctional ETLs that simultaneously boost efficiency and durability, marking a significant step toward viable perovskite photovoltaics.