Study Of Voltage Loss In PbS Quantum Dot Solar Cells

Lead sulfide colloidal quantum dots have been extensively investigated by many researchers because of their solution processability,tunable bandgap and multiexciton effects.In the past decade,thanks to the improvement of synthesis method and optimization of device structure,the performance of lead sulfide quantum dot solar cells has been developed rapidly,from the initial 3%to 15.45%today.However,there is still a large gap on device performance of lead sulfide colloidal quantum dot solar cells compared to traditional silicon solar cells and emerging perovskite solar cells.A major reason for the limitation is the significant open-circuit voltage loss in lead sulfide quantum dot solar cells.Energy loss can occur due to nonuniform quantum dot size and insufficient quantum dot surface passivation,as well as nonradiative recombination of charge carriers at the interface.Our group has recently developed the one-step synthesis of lead sulfide quantum dot inks at room temperature,which not only solves the tedious and expensive problems of previous quantum dot synthesis,but also greatly simplifies the device preparation process.And more importantly,it provides a new method to improve surface passivation,allowing for the direct acquisition of iodine-capped quantum dots,which completely avoids defect regeneration caused by ligand exchange and helps to further address the energy loss issue of quantum dots.In this thesis,based on the direct synthesis of quantum dot inks at room temperature method,we will conduct an in-depth study on both quantum dots synthesis and interface modulation in order to prepare lead sulfide quantum dot solar cells with low voltage loss and high performance.The main research work in this paper is as follows:(1)In-situ synergistic passivation of quantum dot active layer reduces voltage loss in solar cells.Insufficient surface passivation resulting in high open-circuit voltage loss is currently the main factor limiting the efficiency of lead sulfide colloidal quantum dot solar cells.This work introduces short-chain functional molecules and iodine ligands in the direct synthesis method to synergistically passivate the quantum dot surface.These ligand molecules participate in the nucleation and growth process of quantum dots and can form a thermodynamically optimal coordination with the quantum dot surface,thereby improving the surface passivation effect.The quantum dot semiconductor ink obtained by this method exhibits the highest photoluminescence quantum yield(PLQY)among all photovoltaic lead sulfide quantum dot semiconductor inks,reaching 24%,which is more than twice the average PLQY value(about 10%)reported.Based on these quantum dots,a lead sulfide quantum dot solar cell with an open-circuit voltage of 0.68 V and a performance of 12.73%was ultimately prepared.This study offers significant knowledge for enhancing the passivation of quantum dots and showcases the tremendous potential of direct synthesis approaches for producing lead sulfide quantum dot semiconductor ink.(2)Passivation of the interface of the hole transport layer reduces the voltage loss in solar cells.Lead sulfide quantum dot solar cells commonly use ethanedithiol as a hole transport layer(HTL)material.However,studies have found that ethanedithiol has high reactivity and can cause damage to the underlying active layer quantum dots during device preparation,introducing defects and leading to nonradiative recombination of charge carriers at the interface,ultimately resulting in reduced open-circuit voltage.In this work,we screened numerous ligand molecules based on the principle of preserving the passivation effect of thiol molecules while possessing low reactivity,and ultimately selected 3-mercaptopropionic acid as the hole transport layer for lead sulfide quantum dot solar cells.Based on this hole transport layer,a solar cell with an open-circuit voltage of 0.71 V and a power conversion efficiency of 13.3%was successfully fabricated.The open-circuit voltage loss of this cell is only 0.35 V,which is the lowest reported in highly efficient lead sulfide quantum dot solar cells to date.The development of the one-step method for synthesizing lead sulfide quantum dot semiconductor ink at room temperature is of great significance for advancing the development of quantum dot solar cells.Through further exploration of this synthesis method and photovoltaic devices,it is hoped that the issue of significant voltage loss can be resolved,thus promoting the rapid development of quantum dot solar cells towards low cost and high efficiency.