Photovoltaic Properties From Novel Optoelectronic Polymers And Its Devices

With the development of the industry,the problems of energy sources crisis and air pollution have became more and more serious.Photovoltaic(PV)cells now catch more and more focus of research to because they are clean energy sources.Organic materials and polymers are excellent candidates for use in photovoltaics because of their outstanding performance such as hightly p-systems,wide p-p^*gap,low-costing,light weight flexibility.However,there are still some problem such as immature theory,low effectivity,short life and weak stability,so that they are still be study in laboratory.In this thesis,photovoltaic properties from two novel polymers poly(1,4-bis(1-cyano)-vinylenephenylene 3,7-N-octylphenothiazinylene)(PQP)and poly(1,4-bisvinylenephenylene 3,7-N-octylphenothiazinylene)(PQB)were investigated. The PV properties of PQB were studied particularly.The structures ITO/PNB/Al, ITO/PQB/PTCDI-C13/Al,ITO/PQB/CuPc/Al were prepared.Photovoltaic responses under a white LED were observed.In ITO/PQB/Al and ITO/PQB/CuPc/Al,the open circuit voltage(V_oc)were 0.37 V and 0.48 V respectivly.The short current density(J_sc) were 0.024 mA/cm² and 0.25 mA/cm².The difference of V_ocindicated that besides the work functions of electrodes,the V_ocof double layers device was also influence by other factors such as the HOMO level of the donor and the LUMO level of the acceptor. The improvement of J_scindicated that the effective transmission of charges in the double layer devices.In comparison of optical absorption and photocurrent spectra,it was demonstrated that the excitons could be separated and further generated carrier drifting to the opposite electrodes more efficiently in the double layer devices.PQB-CuPc PV devices were investigated.Compared with CuPc/PQB device, PQB/CuPc device showed a better slope of J-V characteristic.In PQB/CuPc device,the J_scwas 0.065mA/cm² and the fill factor(FF)was 0.3,which were both higher than that in CuPc/PQB device.There was a similar result in the PQB-Alq₃ devices.The investigation indicated that the PQB was used as donor and CuPc was used as acceptor, which were propitious to carriers to transmit after the excitions were separated.In PQB/CuPc and CuPc/PQB devices,the polarity of the Voc was uniform.It might result from that there were other interfaces,which contributed to the separation of excitions. The different J_scmight due to the different ability to transmit electrons and holes of materials. Furthermore,PEDOT-PSS and LiF were inserted to the ITO/CuPc/Al device. PEDOT-PSS promoted holes to inject and collect at ITO due to the work function of PEDOT-PSS(5.1 eV)is higher than the one of ITO so that the Jsc could be enhanced. Furthermore,PEDOT-PSS layer could smooth out the uneven surface of ITO so as to reduce leakage current and improve the FF and shunt resistance(R_p).The LiF layer could form a dipole layer between the film and Al cathode,which lowered the work function of cathode,which enhanced the the build-in potential and thurs Voc.Lastly,the PV characteristics under different light intensity were tested and the effect of light intensity on the performance of PQB/CuPc devices was investigated primarily.