Perovskite Solar Cells Utilizing Efficient Charge Transfer Materials

Organic-inorganic hybrid perovskites(typically CH3NH3 Pb X3,with X = I,Br,or Cl)are extremely promising materials for next generation photovoltaic applications owing to their high light absorption coefficient,low exciton binding energy,and long charge-carrier diffusion length.During the past few years,the power conversion efficiencies(PCEs)of perovskite solar cells(PSCs)have dramatically increased from 3.8 to 22.7%,situating them at the forefront of solution-processing photovoltaic devices.This thesis summarizes the development of PSCs and demonstrates efficient perovskite-based solar cells with superior charge transfer materials.The widespread electron-transporting layer(ETL)like Ti O2 often requires high-temperature(>450 °C)sintering,which is not desired for the fabrication of flexible devices.Here,we demonstrate high-efficiency planar PSCs,using room-temperature sputtered niobium oxide(Nb2O5)as the ETL.The amorphous Nb2O5(labeled as a-Nb2O5)ETL,without any heat treatment,can give a best PCE of 17.1% for planar PSCs.Interestingly,the crystalline Nb2O5(labeled as c-Nb2O5),with high-temperature(500 °C)annealing,results in a very similar PCE of 17.2%,indicating the great advantage of a-Nb2O5 in energy saving.We thus carried out systematical investigations on the properties of the a-Nb2O5 film.The Hall effect measurements indicate both high mobility and conductivity of the a-Nb2O5 film.Kelvin probe force microscopy measurements define the Fermi levels of a-Nb2O5 and c-Nb2O5 as-4.31 and-4.02 e V,respectively,which allow efficient electron extraction at the Nb2O5/perovskite interface,regardless of the additional heat treatment on Nb2O5 films.Benefitting from the low-temperature process,we further demonstrated flexible PSCs based on a-Nb2O5,with a considerable PCE of 12.1%.The room-temperature processing and relatively high device performance of a-Nb2O5 suggest a great potential for its application in optoelectronic devices.Halide perovskite nanocrystals(NCs)are currently attracting increasing attention,having already shown great potential as next generation materials for optoelectronic devices.NC materials offer large-scale colloidal synthesis and decouple crystal growth from film deposition,more importantly;these materials can be processed using industrially solvent at room temperature under ambient conditions.All these advantages enable their application in photovoltaic devices.Quite recently,the power conversion efficiency of state-of-the-art quantum dot(QD)solar cells has exceeded 13% due to the emergence of Cs Pb I3 halide perovskite QDs.Here,we demonstrate highly efficient Cs Pb I3 QDs solar cells with a best PCE of 11.51% using variable conjugated polymers as hole conductors,which simultaneously offers room-temperature and air processing for easily processed and highly reproducible solar cell devices.Because of the ease of use and decent efficiency provided by this device structure,our discovery could find use in fully exploiting the potential of various polymer and NC material systems,and also open up new opportunities to improve performance halide perovskite NCs optoelectronic devices.