Fabrication And Characterization Of Organic Solar Cells Based On Narrow-Bandgap Acceptor Photovoltaic

Recently,the emergence of non-fullerene fused ring electron acceptors greatly facilitates the development of organic solar cells(OSCs).In comparison with fullerene derivatives,both the absorption spectra and molecular energy levels of non-fullerene electron acceptor materials could be tuned by modulating their molecular structures.This character renders them the ability to achieve well matching with various bandgap donor materials and thus improve the power conversion efficiency of various kinds of photovoltaic devices.The appearance of narrow bandgap electron acceptors provides opportunity for developing high performance narrow bandgap and semitransparent devices.In addition,most OSCs reported in the literature are processed with halogenated solvents,which is not compatible with the industrial production in the future and sustainable development of humankind community.Therefore,developing environmentally friendly solvent processed high 'performance non-fullerene OSCs is greatly meaningful.In this paper,we carried out research work from three aspects:developing narrow bandgap acceptor photovoltaic materials-based non-flullerene OSCs,developing high performance semitransparent OSCs and developing environmentally friendly solvent processed highly efficient non-fullerene organic solar cells.The main results are as follows:1.A new narrow bandgap polymer electron donor material PBTT was designed and synthesized.When blending with non-fullerene small molecular electron acceptor IEICO,the OSCs based on narrow bandgap photovoltaic materials(PBTT:IEICO)obtained a PCE of 9.5%,which is higher than 7.3%PCE of PTB7-Th:IEICO-based OSCs.This result demonstrates that PBTT is a high performance narrow bandgap polymer donor.Furthermore,the cell has broad and strong photo responses in long wavelength region thus it is a promising candidate to be implemented in highly efficient tandem OSCs performing as a rear cell.2.The narrow bandgap polymer electron donor material PTB7-Th and narrow bandgap non-fullerene small molecular electron acceptor material ACS8 which possess very weak absorption in the human eyes sensitive region(400-600 nm)were chosen to fabricate high performance non-fullerene semitransparent OSCs.The solvent additive PN was utilized to optimize the morphology of blend film.The semitransparent OSCs based on PTB7-Th:ACS8 achieved an optimal PCE of 11.1%with an average visible transmittance(AVT)of 28.6%.This PCE is one of the highest values reported in the literature for semitransparent OSCs.The semitransparent devices with an AVT of 43.2%exhibited a PCE of 9.4%and the color rendering index(CRI)of the cell is 91,which demonstrated an excellent semitransparent performance.3.The polymer electron donor material PBPD-m and non-fullerene small molecular electron acceptor material IT-4F were chosen to fabricate high performance non-fullerene OSCs processed with environmentally friendly solvent system(o-Xylene/DPE).The corresponding OSCs obtained an optimized PCE of 10.7%and the role that solvent additive DPE played in improving the photovoltaic performance of the cells was studied.