| The Cu2ZnSn(S,Se)4(CZTSSe)thin film material has high light absorption coefficient(greater than 104 cm-1),adjustable band gap(1.0～1.5 eV)and good resistance to light failure,In addition,the constituent elements are abundant and safe on the earth.So it is non-toxic and very suitable for the development of high-efficiency,low-cost,stable performance solar cells,and its theoretical limit efficiency can reach 32.8%.However,the current maximum conversion efficiency(PCE)of CZTSSe thin-film solar cells is only 12.62%.One of the main reasons affecting the efficiency improvement is the poor quality of CZTSSe crystals,the existence of a large number of Snzn,Cuzn and Snzn deep-level defects and grain boundary defects,resulting in a large open circuit voltage loss of the solar cells.The previously reported works have shown that ion doping is an effective strategy to solve these shortcomings.If the Sn is replaced by a trivalent element,the open circuit voltage loss can be effectively reduced.Both Y and Bi are trivalent elements.There are theoretical research reports that Y in CZTSSe can passivate grain boundary and surface defects,thereby reducing open circuit voltage loss.If Sn is replaced by Bi,the absorption coefficient of CZTSSe can be increased,thus improving the conversion efficiency of CZTSSe solar cells.However,experimental research on the doping behavior of Y and Bi in CZTSSe and the conversion efficiency of CZTSSe solar cells still need to be carried out.For this reason,this thesis has carried out research on the preparation of Y and Bi-doped CZTSSe thin films and corresponding solar cells,and the doping behavior of Y and Bi in CZTSSe and its influence on the photovoltaic performance and conversion efficiency of CZTSSe solar cells,obtain the following research results:1.A pure kesterite structure p-type CZTSSe(CZTSSe:Y)film with a nominal doping amount of Y of 0-7%(the actual doping amount is 0-2.5 at.%)was prepared by the sol-gel method.We found that Y is not doped into the crystal lattice of CZTSSe,and it is presented in the grain boundary of CZTSSe.In the selenization process,Y was formed Y2Se3.Furthermore,we found that the appropriate Y doping can increase the grain size and density,reduce hole concentration and resistivity.2、For CZTSSe:Y solar cells with a nominal Y doping content of 0-5%,the photovoltaic parameters Voc,Jsc and FF increase with the increase of Y doping content,and the conversion efficiency PCE increases from 2.65%to 5.67%.For solar cells with a nominal Y doping amount of 5-7%,the photovoltaic parameters decrease with the increase of Y doping amount,and the conversion efficiency PCE decreases from 5.67%to 2.90%.The increase of PCE can be attributed to the increase of photoelectric current density(JL)and the decrease of parallel conductance(Gsh),series resistance(Rs)and reverse saturation current density(J0).The decrease of PCE was mainly due to the increase of Gsh,Rs and J0.3、With the increase of Y nominal doping amount,the increase of JL can be attributed to the decrease of CZTSSe hole concentration,which leads to the increase of depletion layer width,The decrease in GSh,RS,and JO can be attributed to the increase in CZTSSe crystal grain size and density,which leads to a decrease in interface leakage,a decrease in bulk resistance,and a decrease in carrier recombination at the interface and in the bulk crystal.4、A pure kesterite structure CZTSSe:Bi film with a nominal Bi doping concentration of 0-10%(the actual concentration is 0-0.45 at.%)was prepared by using the sol-gel method with the Se technique.It is found that Bi is not doped in the CZTSSe crystal lattice,but may be doped in the CZTSSe grain boundary.In addition,we found that appropriate Bi doping can increase the size and density.5、When the nominal Bi doping concentration is 0-8%,photovoltaic parameters of CZTSSe:Bi solar cells increase with the increase of Bi doping concentration,and the PCE increases from 3.85%to 6.21%.When the nominal doping concentration is 8-10%,the photovoltaic parameters decrease as the doping concentration increases,and the PCE decreases from 6.21%to 2.98%.The influence of Bi doping on PCE comes from the change of JL,GSh,RS and JO with the Bi doping concentration.6、With the increase of Bi doping concentration,the increase of JL can be attributed to the Bi passivation CZTSSe grain boundary acceptor defect,which reduces the charge density in the depletion layer.The decrease of Rs can be attributed to the improvement of CZTSSe crystal quality and the decrease of bulk resistance,The decrease in GSh can be attributed to the increase in the flatness and density of the film surface quality,resulting in a decrease in interface leakage current.The decrease in JO is attributed to the better quality of the crystals in the body and surface of CZTSSe and the increase of the built-in electric potential,which leads to a decrease in the recombination of carriers in the CZTSSe and the CZTSSe/CdS interface. |
PDF Full Text Request