ETL-Free Perovskite Solar Cells with an Efficiency of 19.81% in Open Air

Electron transport layer (ETL)-free perovskite solar cells (PSCs) have garnered significant attention due to their simple manufacturing process. However, containing ETL results in blocking holes and suppressing charge recombination. Herein, the titanium dioxide (TiO2)-doped carbon nanofibers (TiO2/C NFs) via electrospinning were introduced into the perovskite absorber layer. The one-dimensional TiO2/C NFs provided an additional charge transport channel to promote the carrier transfer and suppress nonradiative recombination. Carbon nanofibers with high conductivity could also improve the electrical conductivity of perovskite. Moreover, TiO2/C NFs functioned as the nucleation sites to regulate the preferred orientation of perovskite crystals. Finally, the power conversion efficiency (PCE) of rigid PSCs with TiO2/C NFs was significantly improved from 18.07 to 19.81%, with an enhanced stability of only 11% degradation after exposure to an ambient environment for 300 h. In addition, the TiO2/C NFs-optimized flexible devices exhibited a PCE of 17.61%. Highly flexible TiO2/C NFs incorporating effectively improved the bending stability, wherein the flexible PSCs without and with TiO2/C NFs retained 84.27 and 48.33% of the original PCE after 6000 bending cycles (radius: 3 mm), respectively. This work highlights a significant application of TiO2/C NFs in developing high-efficiency and well-stability minimalist PSCs.