Research On Additives Regulating The Morphology And Vertical Phase Separation Of Active Layers In Polymer Solar Cells

Polymer solar cells?PSCs?have become one of the important technologies for utilizing solar energy in the next generation owing to the advantages of low cost,environmental protection,flexibility,semitransparency,and large-scale production.Through continuous efforts including designing and synthesizing donor or acceptor materials,interface modification,morphology optimization,and device structure,the power conversion efficiency?PCE?of single-junction PSCs has exceeded 17%,showing a bright industrialization prospect.Excellent morphology of active layer is conducive to achieving a PSCs with high PCEs,and the use of solvent additives is a simple and effective method in optimizing the morphology of the active layer,so it is necessary to study the mechanism of solvent additives.In this paper,narrow band gap polymer PTB7-Th and fullerene PC₇₁BM are used as the donor and acceptor,respectively.Through adjusting the type and content of solvent additives,the device performance is optimized.Furthermore,the effects of different solvent additives on the morphology and vertical phase separation of PTB7-Th:PC₇₁BM are studied,and explained its relationship with device performance.The specific content is mainly divided into the following three parts:?1?To improve the photovoltaic performance based on PTB7-Th:PC₇₁BM,a new high boiling point solvent additive diphenyl sulfide?DPS,295??was used and the effect mechanism of DPS was investigated.The effect of DPS contents on photovoltaic device performance was illustrated by preparing photovoltaic devices based on PTB7-Th:PC₇₁BM with different DPS contents.Through the characterization of time-of-flight secondary ion mass spectrometer?TOF-SIMS?,water contact angle?WCA?and grazing incidence wide-angle X-ray scattering?GIWAXS?,the effect mechanism of DPS was analyzed.The result indicated that DPS not only adjust the vertical distribution of donor and acceptor components,but also enhance the molecular packing,thus,boosted the exction separation,charge transport and collection,PCE increased from 7.99%to 9.71%.?2?A new non-toxic food additives named Benzyl salicylate?BS,335??was employed for boosting the inverted devices based on ITO/ZnO/PTB7-Th:PC₇₁BM/MoO₃/Ag,and then,the main mechanism of BS was illustrated.Meanwhile,the effect of BS contents on photovoltaic devices was studied by fabricating the corresponding devices,which showed that a fault tolerance within a certain volume range?1%?4%?and the PCE of photovoltaic devices reached above 8.83%.Subsequently,the effect of BS on the photovoltaic performance was studied.The results revealed that a good solubility for fullerenes was presented on BS,which made PC₇₁BM migrate to the bottom of active layer,forming a PTB7-Th enrichment region and a PC₇₁BM enrichment region on the surface and bottom of the active layer,respectively,thus,boosts carrier extraction and reduces carrier recombination,fill factor?FF?and short-circuit current density(J_SC)were improved significantly.?3?To enhance the photovoltaic performance of ITO/ZnO/PTB7-Th:PC₇₁BM/MoO₃/Ag photovoltaic devices,the new green additive benzyl benzoate?BB,323??was used and the related mechanism was studied.The PCE achieved an improvement from 4.83%to 9.43%when 1%BB was adding to the PTB7-Th:PC₇₁BM active layer,which was attributed to the optimized active layer morphology.The results indicated that the active layer with 1%BB processed can obtain a better phase separation size,increase the donor/acceptor interface area,and promote exciton dissociation and charge transport.Moreover,the water contact angle?WCA?measurements indicated that the content of PTB7-Th on the surface is increased when the active layer are processed with 1%BB,thereby obtaining high mobility and less recombination loss,achieving a device with high fill factor and short-circuit current density.