Morphology Control And Performance Study Of Organic Solar Cells Based On Novel Non-fullerene Acceptors

Organic solar cells,showing several advantages such as low-cost fabrication,flexibility and light weight,have attracted considerable attention in both academia and industrial communities.In recent years,the power conversion efficiency（PCE）of both single-junction and tandem devices have been dramatically increased and exceeded 17%.Such high values are attributing to the quick development of non-fullerene acceptors.In comparison with fullerene acceptors,various design strategies are available to tune the absorption spectra and energy level of non-fullerene acceptors,allowing better flexibility in realizing donor acceptors with tunable absorption and band structure.In addition,the device optimization via morphology control is also crucial to improve the performance of device.In this study,high performance organic solar cells based on small molecule non-fullerene acceptors and polymer acceptors were fabricated.Then the underlying charge transport and recombination behaviors,device morphology evolution,etc.were studied.This thesis is divided into three parts.In the first part,organic solar cells based on non-fullerene acceptor BDTIC with heptacyclic S,N-heteroacene core were fabricated.When BDTIC was paired with donor polymer PBDB-T to fabricate organic solar cells,after optimizing the weight ratio of donor/acceptor（D/A）,thermal annealing,and solvent additive,the optimized device achieved a best power conversion efficiency of 12.07%with a J_sc of 20.0 m A cm^-2and a V_oc of 0.88 V,higher than the as cast device without solvent additive（9.92%）.The high photovoltaic performance is resulted from the broad absorption,weak bimolecular recombination,efficient charge separation and collection,and favorable blend morphology.In the second part,organic solar cells based on two naphthalene diimide（NDI）based polymer acceptors Si-Th（with one side chain incorporating siloxane-functionalized substituent）and DSi-Th（with two side chains incorporating siloxane-functionalized substituent）were fabricated and studied.The devices based on Si-Th and DSi-Th as acceptors achieved PCEs of5.75%and 4.72%,respectively,higher than the device based on PNDI-2HD without siloxane-functionalized substituent（PCE=4.30%）.The increased V_oc of device based on Si-Th owes to higher wettability between active layer and electron transport layer.After employing the SCLC,light intensity dependence of J_sc and V_oc,and J_ph versus V_eff tests,it was found that the device of PTB7-Th:Si-Th achieved higher charge mobilities,charge generation rate,exciton dissociation and lower bimolecular recombination,resulting in higher J_sc,FF,and PCE.In the third part,device based on a novel non-fullerene acceptor PDI-I-Ph with photoinduced E/Z isomerization was studied.Without the photoinduced E/Z isomerization,the optimized device based on PDI-I-Ph achieved a PCE of 4.34%.After ultraviolet（UV）treatment from 0 to 25 min,the J_sc and PCE of the devices were gradually reduced.It was attributed to the absorption enhancement in the long-wavelength lower than the absorption decrease in the short-wavelength.In the meantime,semitransparent device was fabricated and found that with the increase of UV time,the average transmittance（AVT）of the device can be increased from24.8%to 28.4%along with color changed.