RESUMO
Printable mesoscopic perovskite solar cells (p-MPSCs) do not require the added hole-transport layer needed in traditional p-n junctions but have also exhibited lower power conversion efficiencies of about 19%. We performed device simulation and carrier dynamics analysis to design a p-MPSC with mesoporous layers of semiconducting titanium dioxide, insulating zirconium dioxide, and conducting carbon infiltrated with perovskite that enabled three-dimensional injection of photoexcited electrons into titanium dioxide for collection at a transparent conductor layer. Holes underwent long-distance diffusion toward the carbon back electrode, and this carrier separation reduced recombination at the back contact. Nonradiative recombination at the bulk titanium dioxide/perovskite interface was reduced by ammonium phosphate modification. The resulting p-MPSCs achieved a power conversion efficiency of 22.2% and maintained 97% of their initial efficiency after 750 hours of maximum power point tracking at 55 ± 5°C.
RESUMO
The low electrical conductivity and the high surface defect density of the TiO2 electron transport layer (ETL) limit the power conversion efficiency (PCE) of corresponding perovskite solar cells (PSCs). Here, the conductivity and defect modulation of the mesoporous TiO2 (mp-TiO2 ) ETL via oxygen vacancy (OV) management by the reduction and oxidation treatment are reported. Reduction treatment via reducing agent introduces abundant OVs into the TiO2 nanocrystalline particles on the surface and at the subsurface. The following oxidation treatment via hydrogen peroxide removes the surface OVs while remains the subsurface OVs, resulting in stratified OVs. The stratified OVs improve the conductivity of TiO2 ETL by increasing carrier donors and decrease nonradiative centers by reducing surface defects. Such synergy ensures the capability of mp-TiO2 as the well-performed ETL with improved energy level alignment, suppressed interface recombination, enhanced carrier extraction, and transport. As a result, printable hole-conductor-free carbon-based mesoscopic PSCs based on the modulated mp-TiO2 ETL demonstrate a highest reported PCE of 18.96%.
RESUMO
The planar SnO2 electron transport layer (ETL) has contributed to the reported power conversion efficiency (PCE) record of perovskite solar cells (PSCs), while the high-temperature mesoporous SnO2 ETL (mp-SnO2 ) brings poor device performance. Herein, we report the application of mp-SnO2 for efficient printable PSCs via oxygen vacancy (OV) management by introducing magnesium (Mg) into the paste. We find that high-temperature annealing suppresses self-doping of SnO2 by reducing OVs. The introduced Mg occupies both the Sn site and interstitial site of SnO2 and promotes the formation of OVs. Lattice Mg tends to induce neutral OVs and interstitial Mg could promote the ionization of neutral OVs for self-doping. The synergy effect on OVs increases the carrier density and upshifts the Fermi level energy of mp-SnO2 , ensuring its capability as the well-performed ETL with trap-less charge transport and suppressed surface recombination for dramatic improved device PCE from 6.62 % to 17.25 %.
