•Stable monolithic hole-conductor-free PSCs were fabricated using TiO2 nanoparticle binding carbon films.•Carbon films were condensed by dehydration between surface hydroxyls from TiO2 nanoparticles and carbon particles.•A reduced sheet resistance from 10 to 2.74 Ω/sq was obtained for carbon films.•Condensed carbon film is beneficial for formation of perovskite crystallites.•Efficiency of 11.07% and stability of 1000 h were achieved.Using TiO2 nanoparticles as binders, highly conductive carbon films were prepared and used to fabricate monolithic hole-conductor-free perovskite solar cell in air. Carbon films were condensed by dehydration reaction between surface hydroxyls from both TiO2 nanoparticles and carbon particles, which is beneficial for adhesion ability and conductivity of carbon film, and the formation and filling properties of perovskite crystallites in the monolithic structure of “FTO/CTiO2/M-TiO2/M-ZrO2/Carbon” (C-Compact, M-Mesoporous). A reduced sheet resistance from 10 to 2.74 Ω/sq was obtained for carbon films annealed under relatively low temperature annealing. Confined distribution of perovskite crystallites in the region containing M-TiO2/M-ZrO2 layers and bottom of carbon film was obtained from 350 °C annealing, which helped to achieve upgraded power conversion efficiency (reverse scan) from 5.40 (±1.32) % to 9.21(±1.04) % (averaged) and 11.07% (champion) at testing area of ∼0.18 cm2, as well as stability of 1000 h in relative high humidity environment (RH:70–90%). The air-compatible fabrication process, sound device ability as well as low-cost of carbon materials make such monolithic device structure realistic candidate for mass production of perovskite solar cells.Download high-res image (313KB)Download full-size image

•A facile solution-based method was developed to synthesize TiO2 nanoparticles (NPs).•The PSCs with a TiO2 NPs buffer layer have excellent improvement in PCE and stability.•The conventional structure PSC with TiO2 NPs based on P3HT:PCBM shows a PCE of 4.24%.•The TiO2 NPs play as an efficient ETL and HBL as well as optical spacer layer in PSCs.•TiO2 NPs have potential applications in PSCs, especially for large-area printed PSCs.TiO2 sols synthesized with a facile solution-based method were used as a buffer layer between the active layer and the cathode Al in conventional structure polymer solar cells (PSCs). Using transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) and atomic force microscopy (AFM), the morphological and crystallographic properties of synthesized TiO2 nanoparticles (TiO2 NPs) as well as the buffer layer were studied in detail. It was observed that by increasing H2O in the process of peptization both the crystallinity and particle size of TiO2 NPs were enhanced, while the particles in sol showed a narrower size distribution conformed by dynamic light scattering. Inserting TiO2 NPs as a buffer layer in conventional structure PSCs, both the power conversion efficiency (PCE) and stability were improved dramatically. PSCs based on the structure of ITO/PEDOT:PSS/P3HT:PCBM/TiO2 NPs/Al showed the short-circuit current (Jsc) of 12.83 mA/cm2 and the PCE of 4.24%, which were improved by 31% and 37%, respectively comparing with the reference devices without a TiO2 buffer layer. The stability measurement showed that PSC devices with a TiO2 NPs buffer layer could retain 80% of the original PCEs after exposed in air for 200 h, much better than the devices without such a buffer layer. The effect can be attributed to the protection by the buffer layer against oxygen and H2O diffusion into the active layers. The observations indicate that TiO2 NPs synthesized by facile solution-based method have great potential applications in PSCs, especially for large-area printed PSCs.Graphical abstract