The fineenergy-level modulation for

The fineenergy-level modulation for deeper donor HOMO and higheracceptor LUMO is proven to be an effective way to boost the performance of OSCs with improved Voc. Fig. 14 and Table 4 summarize the differences of the LUMO energy levels of theacceptors and HOMO energy levels of the donors, Voc, PCEsand deduced energy losses (through assuming the binding energies for all cases are zero) for all of above four blends. We see thathigher Voc resulted in higher PCE and the higher Voc can beobtained through delicately adjusting the energy levels throughappropriate molecular design. The voltage loss is from two mainsources. One is the energy offset between the bandgap of the donor/acceptor and the energy of the charge transfer state, theother is from the large nonradiative recombination loss. Practically, a driving force is always required for OSCs and energy lossfrom non-radiative recombination is unavoidable. The energylevel modulation by changing the molecular structures may havenegative impacts on light absorption and blend morphology,which finally influences on the optimal value of IE(D)–EA(A) andenergy loss. Therefore, it is important to consider a synergeticeffect of all of factors on device performance and find the optimized balance among all of factors. Optimizing the microscopicparameters of the interface between donor and acceptor thatdetermine loss pathways would benefit for the development ofhigh-performance OSCs with small voltage losses.