The Study On The Performance Of Semitransparent Organic Solar Cells With Different Absorption Characteristics

Energy problem is a critical challenge for our society and human life.Solar cells that use photovoltaic effect to convert solar energy into electricity,are considered to be the key to solve the energy problem.Organic solar cells have the advantage of adjustable absorption,which is conducive to the preparation of semitransparent organic solar cells(STOSCs).At present,STOSCs can achieve power conversion efficiency(PCE)of 8%-12% with visible light transmittance(VLT)of 20%-40%,but to meet the requirement for building integrated photovoltaics(BIPV)applications,the transmittance needs to be further increased to more than40%.Therefore,in order to prepare STOSCs with higher VLTs,it is necessary to analyze the effects of different absorption characteristics of the STOSCs,and to design the device structure reasonably,which are systematically studied in this thesis.In chapter 2,we studied the performance of OSCs based on a high efficiency bulk heterojunction(BHJ)system with different ratio of donor:acceptor(D:A).At the same time,the performance of the STOSCs was further improved by optimizing the device structure.We chose the PM6:Y6-BO BHJ to prepare the opaque OSCs,which deliver efficiency of more than 16%.The VLTs of STOSCs increases with the reduction of the proportion of donor in BHJ,and the highest PCE of the STOSCs is 11.5%,with a VLT of 20.9% when the donor content is 50%.When the donor radio is further reduced to 18.2%,the VLT of the STOSC increased to 24%.However,the highest light utilize efficient(LUE),which is defined as the product of PCE and VLT,was achieved when the donor ratio is 22.2%.In order to explain the effect of different donor ratio on the STOSC performance,we analyzed the carrier properties of the devices.The results show that with the decrease of donor ratio,the hole mobility decreases and the electron mobility increases,which is attributed to the increase of acceptor ratio in the active layer.The imbalance of electron and hole transport induce space charge,which increases the probability of charge recombination and reduces the performance of the device.Therefore,in the chapter,we show that reducing the donor ratio could be an possible way to improve the transparency of the STOSCs while not affecting much on the device efficiency.In chapter 3,we discussed about STOSCs with all-low-bandgap light harvesting components.We chose the low-bandgap polymer PM2 as the donor and blended with the lowbandgap non-fullerene receptor Y6-BO to prepare the active layer.First,by optimizing the opaque device,we obtained a maximum PCE of more than 11% at the donor:acceptor ratio of1:1.5,which is known to be the highest PCE reported for all-low-bandgap organic solar cells.At the same time,through the analysis of the absorption of thin film,it suggested that the absorption of the film increases with the proportion of acceptors.This result is due to the similar absorption range of PM2 and Y6-BO but a higher absorption coefficient of Y6-BO.We use optical simulation to guide the device optimization,which suggests that a higher VLT can be achieved by reducing the active layer thickness and electrode thickness,with the device efficiency reduce to certain extent.According to guideline provided by the optical simulation,PM2:Y6-BO based STOSCs with different device structures were prepared.A STOSC with the highest PCE of about 6% and VLT of about 43% was obtained when the thickness of active layer and the gold electrode was 75 nm and 5nm,respectively.Finally,by comparing the all-low-bandgap based STOSCs with the high-efficiency based OSCs,it shows that the PCE of high-efficiency based STOSCs is significantly better than the all-low-bandgap based OSCs.However,form the perspective of VLT,the all-low-bandgap based STOSCs is significantly better than that of high-efficiency based STOSCs,and also shows a slightly higher LUE.To conclude,in this work,we show the influence of BHJ with different absorption characteristics on the performance of STOSCs.In order to prepare STOSCs with higher VLTs,two ways can be used: using all-low-bandgap system or reducing the proportion of donor.This work also provides a new idea for the designing STOSCs with desired optical property and device performance and pave the way for the commercialization of STOSCs.