Photovoltaic Performance Study Of Copolymer Solar Cells Based On Lactam Units

Polymer solar cells(PSCs)have been considered as a promising photovoltaics technology due to the merits of lightweight,flexibility and roll-to-roll fabrication.Using electron-donating(D)and electron-accepting(A)building blocks to construct D-A copolymers is one of the key strategies toward high performance PSCs.Currently,there are several strategies to improve the power conversation efficiency(PCE)of PSCs,these mainly include developing high-performance photovoltaic materials,optimizing active layer morphology,developing high-performance interface materials,and optimizing device architectures.In this thesis,we mainly focused on the effect of novel D-A copolymer donor materials on the performance of PSCs.The UV-vis absorption spectrum and cyclic voltammetry were used to study the effects of chemical structure of the D-A copolymers on optical properties and electrochemical properties.In addition,the effect of D/A ratio,active layer thickness,DIO content,carrier mobility,balanced charge transport,carrier recombination and active layer morphology on the photovoltaic performances were also investigated in detail.The specific research contents and results are summarized as below.(1)Two copolymers,PBDTBTTP and PBDTiBTTP based on lactam BTTP and iBTTP units,were synthesized to study the impact of isomeric structures on their photovoltaic performances.Compared with PBDTBTTP,PBDTiBTTP possesses smaller bandgap with more efficient light harvest and better molecular packing for higher carrier mobilty.The PBDTiBTTP based solar cell presents lower charge recombination,balanced ?e/?h and uniform morphology.As a result,PBDTiBTTP cell gave a better PCE of 6.51%with higher Jsc and FF compared with PBDTBTTP cell.(2)A low-bandgap D-A copolymer of PDTP4TFBT based on dithieno[3,2-b:2',3'-d]pyridin-5(4H)-one unit(DTP),was used as the donor material for PSCs with PC71BM or ITIC as the acceptor.PDTP4TFBT:PC71BM and PDTP4TFBT:ITIC solar cells gave power conversion efficiencies(PCEs)up to 8.75%and 7.58%,respectively.It was found that 1,8-Diiodooctane(DIO)has a large influence on the film morphology and device performance for fullerene and non-fullerene solar cells.DIO inhibits the active materials from forming large domains and improves PCE for PDTP4TFBT:PC71BM cells,while it promotes the aggregation and deteriorates performance for PDTP4TFBT:ITIC cells.The ternary-blend cell based on PDTP4TFBT:PC71BM:ITIC(1:1.2:0.3)gave a decent PCE of 9.20%.(3)A polycyclic aromatic lactam building block,[2,2'-bidithieno[3,2-b:2',3'-d]pyridine]-5,5'(4H,4'H)-dione(BDTPi),was used as the acceptor unit for PSCs.We studied the effects of two BDTPi-based D-A conjugated copolymers of PThBDTPi and PSeBDTPi as donor materials on the performance of PSCs.In addition,the effect of D/A ratio,active layer thickness,DIO content,carrier mobility and active layer morphology on the photovoltaic performances were also investigated.The power conversion efficiencies for PThBDTPi and PSeBDTPi up to 8.11%and 6.50%,respectively,in PSCs with PC71BM as the acceptor.