Study On Improving The Performance Of Organic Solar Cells Based On Active Layer Doping Technology

With the continuous improvement of photovoltaic technology and society's urgent need for clean energy,photovoltaic industry has become the focus of new energy development.Organic solar cells?OSCs?featuring properties of low cost,light weight,flexibility and easy solution-based processing have made great progress in the recent decade.Recently,through research on bulk heterojunction organic solar cells,an effective method of expanding the light absorption range has been found to increase short-circuit current density(J_SC)and energy conversion efficiency?PCE?.This article mainly focuses on broadening the absorption spectrum and the matching of energy level structures,and introduces the third component to prepare bulk heterojunction organic solar cells to realize complementary absorption,promoted exciton dissociation,enhanced charge transport,and optimized surface morphology of the film,and then the overall performance of organic solar cells is improved.In the second chapter,a high crystallinity small molecule DR3TBDTT was introduced into the binary system PTB7-Th:PC₇₁BM to prepare ternary organic solar cells.Ternary organic solar cells?OSCs?with one acceptor(PC₇₁BM)and two donors,i.e.,one polymer?PTB7-Th?and one small molecule?DR3TBDTT?have been fabricated.We substantially improved PCE from the best reported value of 7.53%to 9.25%with increase of 22.8%,and an averaged PCE of 9.25%is obtained due to the improvement of the fill factor?FF?and the short-circuit current density(J_SC).After analysis,it was found that both DR3TBDTT and PTB7-Th belong to the planar structure and have good molecular compatibility.The results of atomic force microscopy?AFM?indicate that a highly ordered molecular arrangement could be obtained by forming alloy with two miscible donors,and the doping of DR3TBDTT not only protects the long distance charge transport in the original binary system,but also improves the size of phase separation of the active layer within the ternary OSCs,thus forming the ordered nano morphology,which can improve the mobility of hole and reduce the charge recombination.In the third chapter,the third component 1-bromo-4-nitrobenzene?1-Br-4-Nb?was introduced into the active layer of PTB7-Th:PC₇₁BM to promote exciton separation and speed up electron transfer.A PCE of 8.95%is achieved for the organic solar cells?OSCs?with15wt%1-Br-4-Nb,which is a 18%enhancement in PCE compared with the binary OSCs based on PTB7-Th:PC₇₁BM.Atomic force microscopy?AFM?measurements indicated that the ideal morphology can be formed.The charge generation properties were studied by internal quantum efficiency?IQE?and photocurrent density(J_ph),revealing that charge transport was facilitated significantly,which favors higher J_SC and FF.In the fourth chapter,we fabricated dual-acceptor organic solar cells through introducing a fullerence acceptor PC₇₁BM with high electron mobility and other advantages into PBDB-T:ITIC system.In such a hybrid device,the absorption range of non-fullerene acceptor ITIC is complementary to that of PC₇₁BM,which can broaden the absorption range and enhance the intensity.Moreover,the energy levels of PC₇₁BM matches well with PBDB-T and ITIC.The appropriate LUMO energy level can reduces the energy loss,and increase short-circuit current density.Since PC₇₁BM mainly plays a role in improving charge transfer in the dual-acceptor device,the exciton separation becomes relatively balanced with the increase of the doping amount of PC₇₁BM.Meanwhile,the PC₇₁BM helps to suppress charge recombination,enhance ITIC light absorption.By optimizing the doping ratio of PC₇₁BM,the PCE of the three-component device significantly increased to 9.57%.