Spectroscopic Study Of Narrow Band Gap Polymer Photoelectric Materials

With the continuous development of human society,the problems of energy exhaustion and environmental pollution are becoming more and more serious,and the search for new and pollution-free renewable energy is becoming a worldwide issue.Solar energy,with its almost endless reserves and clean environment,has become a hot topic in solving the energy crisis.Organic polymer solar cells own the characteristics of low price,relatively simple production process and access to make large area products.At the same time,the preparation of polymer films with various mature ways has provided a strong support for the preparation of the battery.However,there are still many problems about the efficiency of organic polymer solar cells,and how to use a low band gap,wide absorption spectrum of polymer photovoltaic materials to improve the efficiency of the battery is a research focus of polymer solar cells.In this paper,two new low band gap(LBG)polymer materials are studied,and optical measurement is used to investigate the photophysical processes in the low band gap polymer thin films.It comes out primary result now:(1)First,I have set up an optical measurement system,which can measure absorption spectrum,photoinduced absorption(PA)spectrum and photoluminescence(PL)spectrum.The wavelength range of the spectra covers from visible light to infrared light.High signal to noise ratio has been achieved for detecting weak signal.At the same time,the automatic control and data acquisition of the system was realized by writing programs with Labview.(2)Use the low band gap polymer PBPT as donor material,and non-fullerene N2200 as accepter material to make the bulk heterojunction(BHJ)thin films.PBPT shows a broad absorbance and can capture more solar energy.The alignment of the energy level of PBPT and N2200 allows the electron transfer from PBPT to N2200 and hole transfer from N2200 to PBPT.Use different pump light to get PA spectra,including 447nm continuous wave(CW)laser and 808nm CW laser,whose energy is below the energy gap of PBPT.Both results have shown photoinduced infrared-active vibrations(IRAV).The process of charge transfer in PBPT/N2200 film is verified by this result as well as the quenching phenomenon in the PL spectra.Next,the prepared films were treated by annealing,and differences of different films were studied by PL Spectrum,PL Spectrum and Urbach energy.The experimental results show that the way to enhance solar cells’ efficiency is to control and reduce the defect state as well as improve the crystallization through annealing.(3)Use the low band gap polymer PBPT as donor material,non-fullerene N2200 and fullerene PCBM respectively as accepter material to make the bulk heterojunction(BHJ)thin films.Measure the PL spectra,PA spectra of PTP8/N2200,PTP8/PCBM thin films,and make analysis and comparison of reflective optical process.The experimental results show that there are PTP8 polarons in both blend thin films,but PTP8/N2200 has low charge transfer efficiency than PTP8/PCBM.Although N2200 has strong absorption to near-infrared light,but due to the low efficiency of charge transfer,absorption of sunlight energy cannot be effectively used,leading to the low efficiency of solar cells.Experimental results show that for different donor material,should choose appropriate acceptor materials in order to obtain higher charge transfer efficiency.This result give reference to the research and development of PTP8 low band gap polymer solar cells.