Understanding the correlation between energy-state mismatching and open-circuit voltage loss in bulk heterojunction solar cells

Photoinduced intermolecular charge transfer(PICT)determines the voltage loss in bulk heterojunction(BHJ)organic photovoltaics(OPVs),and this voltage loss can be minimized by inducing efficient PICT,which requires energy-state matching between the donor and acceptor at the BHJ interfaces.Thus,both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT.In this study,an effective method for quantifying the hot state matching of OPVs was developed.The degree of energy-state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor(MF)calculated from the modified optical density of the BHJ.Furthermore,the correlation between the open-circuit voltage(Voc)of the OPV device and energy-state matching at the BHJ interface was investigated using the calculated MF.The OPVs with small absolute MF values exhibited high Voc values.This result clearly indicates that the energy-state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs.Because the MF indicates the degree of energy-state matching,which is a critical factor for suppressing energy loss,it can be used to estimate the Voc loss in OPVs.

Hong–Ou–Mandel interference of two independent continuous-wave coherent photons

Interference between two completely independent photons lies at the heart of many photonic quantum information applications such as quantum repeaters,teleportation,and quantum key distribution.Here,we report the observation of Hong–Ou–Mandel(HOM)interference with two independent continuous-wave coherent light sources that are neither synchronized nor share any common reference.To prepare indistinguishable photons from two independent laser sources,we employ high-precision frequency-stabilization techniques using the 5 S1∕2(F=3)-5P1∕2(F'=3)transition line of 85 Rb atoms.We successfully observe an HOM interference fringe with two independent continuous-wave coherent photons originating from either the frequency-locked or the frequency-modulated lasers.An interference fringe involving two-photon beating is also observed when the frequency difference between the two interfering photons is beyond the spectral bandwidth of the individual coherent photons.We carry out further experiments to verify the robustness of the source preparation regardless of the separation distance between the two independent photon sources.

Two-photon interference between continuous-wave coherent photons temporally separated by a day

An understanding of the phenomenon of light interference forms the kernel underlying the discovery of the nature of light from the viewpoints of both classical physics and quantum physics.Here we report on two-photon interference with temporally separated continuous-wave coherent photons by using a temporal post-selection method with an arbitrary time delay.Although the temporal separation of a day between the photons is considerably longer than the coherence time of the light source,we observe the Hong–Ou–Mandel(HOM)interference of the pairwise two-photon state.Furthermore,we experimentally demonstrate the HOM interference observed in one of the interferometer-output modes by using only one single-photon detector for a large temporal separation.