Enhance Performance Of PbS Quantum Dot Solar Cells By Interface Engineering

In recent years,PbS colloidal quantum dots solar cells have attracted many attentions for their wide spectral response,can be prepared in solution,high stability,low cost and other advantages,and the efficiency has exceeded 12%in a relatively short time.However,interfacial band mismatch and charge transfer limited for distance of quantum dots are still the key problems of limit the further improvement of the efficiency of PbS quantum dot solar cells.In this paper,the interface between FTO/ZnO and PbS quantum dots is optimized based on interface engineering strategy.The interface barrier is reduced by introducing PEI dipole layer into FTO/ZnO interface,and the distance between PbS quantum dots is reduced by external pressure treatment,which significantly improves the solar conversion efficiency of PbS quantum dot solar cells.The specific research contents are as follows.The interface dipole layer was prepared by spin coating PEI solution of different concentration on FTO electrode.Then the ZnO electron transport layer was spinning coated and quantum dot solar cells were constructed.When the concentration of PEI solution is 0.3%,the performance of quantum dot solar cells is optimal:J_sc is increased from 19.46 mA cm-2 to23.2 mA cm-2,V_oc from 0.63 V to 0.65 V,FF from 60.72%to 64.75%,and the maximum efficiency is 9.67%,which is 15%higher than that of the cells without PEI modification.Kelvin probe test showed that the FTO/ZnO interface changed from Schottky contact to ohmic contact.Mott-Schottky test,light intensity dependence test and dark current analysis show that the built-in potential at the interface of ZnO/PbS is enhanced by the insertion of PEI.The above results show that add dipole layer in PEI interface is helpful to promote carrier separation,collect and reduce charge recombination at the interface.The effects of external pressure treatment（0-2 MPa）on PbS quantum dots solar cells were studied.It is found that the performance of solar cell is related to the pressure.The performance of solar cell after 1.5 MPa pressure treatment is the best,and the device efficiency is increased by more than 25%.Pressure treatment within five hours after the preparation of the quantum dot absorption layer can improve the device efficiency.The fluorescence spectra of ZnO/PbS bilayer films and the light intensity dependence of J_sc indicate that pressure treatment can promote the extraction of photogenerated charges from the ZnO electron transport layer.The photovoltage decay test and light intensity dependent Voc test prove that pressure treatment can prolong carrier lifetime and reduce charge recombination at the interface.The red shift of fluorescence emission peak and conductive atomic force microscopy（CAFM）measurements before and after pressure treatment of PbS thin films show that pressure treatment reduces the quantum dot spacing of PbS thin films and improves the charge transfer performance of PbS thin films.The above research shows that external pressure treatment is an effective method to improve the performance of quantum dot solar cells.