Study Of Photovoltaic Materials And Photoactive Layer Morphology For Organic Solar Cells

Organic solar cells(OSCs),as a new generation of solar energy utilization technology,present solution-processability,light weight,semi-transparency and intrinsic mechanical flexibility,demonstrating great potential for development and broad prospects for application.Currently,the power conversion efficiency(PCE)of OSCs based on polymer donor and small molecule acceptor has approached to 19%,which has met the requirements for commercial applications.However,the reported highly efficient photovoltaic materials including donor and acceptor generally show complex molecular structures,long synthesis routes,tedious purification steps and low synthesis yields,which result in high synthesis costs of photovoltaic materials and greatly limit the commercial application of OSCs.In addition,the photovoltaic performance for all-polymer solar cells(all-PSCs)possessing excellent stability still significantly lags behind that of OSCs based on polymer donor and small-molecule acceptor.Because the mophorlogy control of the photoactive layer for all-PSCs is relatively difficult.To address the above two problems,this thesis focuses on the design and development of low-cost and high-performance polymer donor materials and the mophorlogy control of the photoactive layer for OSCs(including all-PSCs),which are mainly as follows:(1)In order to reduce the synthesis cost of the classic fluorinated bithienyl benzodithiophene unit(BDTT-F),we synthesized an α-position fluorinated bithienyl benzodithiophene unit(α-BDTT-F)by exchanging the positions of F atom flexible alkyl chain on the lateral thiophene unit.Compared with the BDTT-F unit,the αBDTT-F unit presents fewer synthetic steps,higher synthetic yields and shorter purification times,thus the synthesis cost is significantly reduced.Theoretical calculation indicates that the α-BDTT-F unit possesses similar twisted conformation and electronic structures as those of the BDTT-F unit.The α-BDTT-F-based polymerα-PBQ10 exhibits similar light absorption and energy levels,better molecular selfassembly behavior and hole transport ability in comparison with those of the corresponding BDTT-F-based polymer PBQ10.In consequence,the α-PBQ10:Y6based OSC demonstrates a slightly enhanced PCE of 16.26%.In addition,the PCE is further improved to 16.77%through subtle microscopic morphology regulation of the photoactive layer with the fullerene derivative ICBA as the third component(2)To improve the photovoltaic performance of all-PSCs,we introduce a lowcost polymer PTQ10 into the PM6:PY-IT blend to finely tune the microscopic morphology of the photoactive layers(PM6:PY-IT).The addition of PTQ10 induced a reduced molecular π-π stacking distance,an increased molecular π-π stacking coherence length and more ordered face-on molecular packing orientation,which enhance the charge separation and transport in the photoactive layer.Moreover,the deeper highest occupied molecular orbital energy level of PTQ10 than PM6 leads to increased open-circuit voltage of the ternary all-PSCs.As a result,a PCE of 16.52%is achieved for PM6:PTQ10:PY-IT based ternary all-PSCs,which is one of the highest PCEs for all-PSCs.In addition,the ternary devices exhibit high tolerance of the photoactive layer thickness with high PCEs of 15.27 and 13.91%at photoactive layer thickness of～205 and～306 nm respectively,which are the highest PCEs for all-PSCs with thick photoactive layers so far.This property is beneficial for large-area fabrication of OSCs.