Investigation Of Doping And Interface Modulation For Perovskite Solar Cell

The hybrid organic-inorganic perovskite materials have attracted considerable interests due to their salient optical and electronic properties,such as strong light absorption ability,small exciton binding energy,long carrier diffusion length,high carrier mobility.The photovoltaic cell with perovskite material has become a very promising new type of solar cell due to its high efficiency,low cost and simple preparation.However,the uncontrollable crystal quality,defective electron transport layer(ETL),serious interface recombination extremely restrict the development of perovskite solar cells(PSCs).This study focused on the generation and separation of photogenerated charges in PSCs.From the perspective of ETL and perovskite quality regulation and interface design,the crystal defects in perovskite are reduced and the transport of the photogenerated carriers at interface is improved,which effectively enhance the performance of PSCs.First,the ions with a suitable ionic radius was choosed and filtrated to achieve the simultaneous regulation of the defect passivation,the photoresponse and the energy level alignment between ETL and perovskite absorption layer.Thus,the extraction efficiency of the photo-generated charge can be improved.Second,additive were introduced in the perovskite precursor to further improve the generation of photogenerated charges.Simultaneously,the passivation layer was introduced at the inerface between perovskite and ETL,which effectively promoted the efficient transport of the photogenerated charges at interface.Third,the influence of volatile acetate and non-volatile acetate on the crystallinity of perovskite was systematically compared.Based on the above methods,the high-quality perovskite film with compactness and flat,prolonged photoluminescence lifetime,and lowered defect density was fabricated,which improved the interface contact between carbon layer/perovskite as well as the generation carriers in perovskite.Finally,modification of the ETL/inorganic perovskite absorption layer interface with europium improved the morphology of the perovskite,promoted the efficient carriers separation at the interface,which greatly improved the photoelectric performance of the PSCs.Co/Eu co-doping strategy is used to introduce Co and Eu into the precursor solution of the TiO2 dense layer by a one-step spin coating method.Co doping passivates the electronic trap-states in TiO2 ETL,improving the charge transport properties.Eu doping enhances the photoresponse of PSCs.Additionally,Co/Eu co-doping upshifted the bottom position of conduction band of TiO2,optimizing the energy level alignment between ETL and perovskite absorption layer,which promoted the efficient photo-generated charges transfer from the perovskite absorption layer to the ETL.By judicious adjusting the amount of the dopant,the champion power conversion efficiency(PCE)of the carbon based hole transport layer(HTL)free PSCs(C-PSCs)is 14.06%.Moreover,stability also exhibit well.Such co-doping strategy provides an promising approach for simultaneously increasing the open circuit voltage and short circuit current density greatly.The insulating layer was developed by spin-coating Al2O3 between ETL/perovskite absorbtion layer in the paintable C-PSCs.In addition,graphitic carbon nitride is introduced into the perovskite precursor.The synergistic regulation mechanism of graphitic carbon nitride and Al2O3 film on the performance of paintable C-PSCs has been in-depth studied.The introduction of graphitic carbon nitride improve the crystal quality of the perovskite,which is characterized by its larger grain size,reduced defects and higher absorption.The built-in potential was improved,leading to an enhanced driving force for charge separation and an extended depletion region for suppressing carrier recombination.More impotantly,the introduction of Al2O3 film hindered the recombination of the electrons in ETM layers with holes left in perovskite layers,promoted the efficient transportation of photo-generated charges.The highest PCE of the C-PSCs is 14.34%.PCE of C-PSCs is～36.6%enhancement compared to that of the control device.In order to improve the poor contact at perovskite/carbon interface in the C-PSCs,volatile acetate and non-volatile acetate were introduced into the perovskite precursor separately to improve the perovskite crystallinity.The influence of volatile acetate and non-volatile acetate on the crystallinity of perovskite was systematically compared.By introducing a very small amount of volatile ammonium acetate through a simple one-step spincoating method,high-quality perovskite layer with lower defect density,larger grain size,and pure perovskite composition without alien atom was obtained,which is more compactness leading to the improvement of contact quality at perovskite/carbon interface.It can be found that the non-radiative recombination decreases and the carrier lifetime increases,which is ascribed to trap passivation by the introduction of ammonium acetate.PCE of C-PSCs is～23%enhancement compared to that of the device without additive.Moreover,stability was also investigated,6%degradation appeared in PCE of volatile ammonium acetate sample after being stored for 1900h in dark.The promoted interface contact of carbon/perovskite and the improved crystallinity of perovskite result in higher efficiency and longer stability of volatile ammonium acetate added PSC.After applying the Al2O3 between ETL/perovskite absorbtion layer,the best PCE of 14.65%is obtained.On the other hand,addition of non-volatile zinc acetate only lead to a slight enhancement of the efficiency due to the cracks in the perovskite.In order to decrease charge accumulation at the ETL/CsPbI2Br perovskite interface,europium nitrate was choosed to treat tin dioxide,and its regulation mechanism to improve the interface was investigated.On the one hand,the morphology and crystallinity of the perovskite is improved,the defects inside the perovskite are reduced.On the other hand,the electron extraction is enhanced,charge accumulation at the ETL/perovskite interface is reduced.Thus,the recombination of photo-generated charges at the interface is inhibited.Finally,the efficient transfer of photo-generated charges is promoted.By finely optimizing the doping concentration,the highest efficiency of the PSCs reach to 16.83%with a Voc of 1.4 V,corresponding to an extremely small Voc deficit of 0.52 V.