High-efficiency Quantum Dot Solar Cells Based On Novel Electron Transport Layers And Quantum Dot Ligand-Exchange Dynamic Manipulation

PbS quantum dots?CQDs?solar cells present high theoretical efficiency,the distinctive ability to broad light harvest range,good ambient stability and convenient solution processing,thus attract much attentions in the photovoltaic researches.High-efficient PbS quantum dot solar cells mainly adopt a heterojunction structure,which composed of metal oxide electron transport layer and quantum dot light absorption layer.However,the low-temperature fabricated electron transport layers present high defect density and low mobility,which affect the improvement of device performance.In addition,the performance of quantum dot solar cells mainly depends on the quantum dot light absorption layer.The key is to obtain high-quality quantum dot films with high density and low surface defects.In this work,we focused on electron transport layers and quantum dot light absorption layer.High-efficiency PbS quantum dot solar cells were fabricated via optimizing electronic transport layers and manipulating phase-transfer ligand exchange dynamics of PbS quantum dots.Specific research results are as follows:1.Sol-gel ZnO materials were excellent electron transport layers?ETLs?for high-efficiency PbS quantum dot solar cells.However,serious defect states in low-temperature prepared ZnO usually deteriorated the carrier recombination at the ZnO/PbS quantum dot interface.We prepared composite ZnO:PEI films,and employed these composite ZnO:PEI ETLs in quantum dot solar cells for the first time?PEI:polyethylenimine?.The introduction of PEI could effectively passivate the ZnO surface defects and improve the crystallinity,resulting in the reduced work function and the increased electron mobility.A series of device mechanism analysis showed that the optimized ZnO:PEI electron transport layer could effectively inhibit the carrier recombination and promote the carrier transport in the device.Consequently,a power conversion efficiency?PCE?of 7.30%was achieved with the ZnO:PEI 5%ETL versus 5.84%for the reference cell.2.SnO₂ electron transport layer was employed to improve the high efficiency and operational stability of PbS quantum dot solar cells.Compared with ZnO,SnO₂ is an excellent electron transport layer material with wider band gap,higher electron mobility and good acid-base stability.However,there is still bits of research on SnO₂/PbS quantum dot solar cells.The influence of annealing temperature and film thickness of SnO₂ was investigated on the device performance.Optimizating the annealing temperature of SnO2 can effectively reduce the residual organics and oxygen defects,enhance the surface passivation,and improve the electron mobility.When the concentration of SnO2 precursor solution was 5%,and the annealing temperature was 200?,the SnO₂/PbS quantum dot device obtained a PCE of 10.12%and a better device illumination stability.3.Dynamics of quantum dot solution-phase ligand exchange was systematically researched for efficient infrared photovoltaics.Developing high stable PbS quantum dot ink was the key to high-efficiency quantum dot solar cells.However,the mechanism of quantum dot ink and the preparation of high-quality quantum dot ink are still the focus of quantum dot solar cells.The dynamics effects of ammonium acetate additives on of ligands exchange,phase transfer and surface passivation process of PbS quantum dots were investigated.The two-sided property of ammonium acetate additive in the preparation of quantum dot ink was proved.As a result,the PbS quantum dot?Eg=1.39 eV?device with moderate AA achieved a PCE of up to 10%.Furthermore,the narrow-bandgap PbS quantum dot devices?Eg=1.05 eV?exhibited a best PCE of 7.47%and J_SC of 30.5 mA/cm².This results demonstrated their promising potential for the subcells of the tandem photovoltaic devices.