External quantum efficiency EQE

The highest efficiency OLED utilizing a spiro-terfluorene (compound 51) in a double confinement device structure [185], reaches an external quantum efficiency (EQE) of 5.3%, or 1.53 cd A-1, with CIE coordinates of (0.158, 0.041). Others using similar double confinement structures have achieved... 

External quantum efficiency (EQE)- This is defined as the total number of photons emitted from the device per electron-hole pair injected into the device. It is represented by f/ext-The external quantum effidency is related to the internal quantum efficiency and is given by (OIDA 2002)... 

A further improvement of MDMO-PPV based bulk heterojunctions was achieved by the application of a new C70 fullerene derivative, which was substituted with the same side chains as PCBM and is therefore called [70]PCBM [170]. Due to the reduced symmetry of C70 as compared to the football sphere (icosahedral symmetry) of Ceo. more optical transitions are allowed and thus the visible hght absorption is considerably increased for [70]PCBM. This led to an improved external quantum efficiency (EQE) of MDMO-PPV based solar cells reaching up to 66% (Fig. 30). As a result the power conversion efficiency was boosted to 3% under AM 1.5 solar simulation at 1000 W/m [170]. 

Fig. 30 Photovoltaic properties of an MDMO-PPV based polymer-fullerene solar cell with an active area of 0.1 cm. a External quantum efficiency (EQE) of [70]PCBM MDMO-PPV cells, spin-coated from chlorobenzene (triangles) and ODCB (squares) and of [60]PCBM MDMO-PPV devices spin-coated from chlorobenzene (open circles) b current-voltage characteristics of [70]PCBM MDMO-PPV devices, spin-coated from ODCB in the dark (open circles) and under illumination (AM 1.5, 1000 W/m squares). The inset shows the I-V characteristics in a semilogarithmic plot. (Reproduced with permission from [170], 2003, Wiley-VCH)...

Fig. 14 Photovoltaic performance of BC 16 and BC 30 after processing from chlorobenzene solutions, a External quantum efficiency (EQE) and b 7-V-curves under AM 1.5G conditions (lOOmWcm-2). (Reproduced with permission from [75]. Copyright 2009 American Institute of...

The quantum efficiency of a device is the ratio of the number of charge carriers collected by the solar cell to the number of photons of a given energy shining on the cell surface. Two types of quantum efficiencies are often quoted the internal quantum efficiency (IQE) that includes the effects of losses through light transmission and reflection and the external quantum efficiency (EQE) that excludes these effects and instead considers only the fraction of photons that were actually absorbed. 

Fig. 5.20. Semi-logarithmic plot of external quantum efficiency (EQE) vs. wavelength. Inset illustrations depict device structures and film thicknesses. The Au/TPD device yields no measurable photoresponse and thus is not shown. Both heterojunction devices (solid and dashed lines) yield orders of magnitude improvement in the EQE over the Au/PTCBI device (dotted line) despite using lower bias voltages. At A = 552nm, the Au/PTCBI/TPD device (dashed) and Au/TPD/PTCBI device (solid) yield EQEs of approximately 8% and 16%, respectively. After accounting for the absorption in the PTCBI/TPD device, we calculate an internal quantum efficiency (IQE) of approximately 140%. This demonstrates that lateral bi-layer heterojunctions are capable of gain...

The incident photon to current conversion efficiency (IPCE) sometimes referred to also as external quantum efficiency (EQE) corresponds to the number of electrons measured as photocurrent in the external circuit divided by the monochromatic photon flux that strikes the cell. The following product expresses this key parameter ... 

The spectral responsivity measurements yield the number of collected electrons per incident photon at each wavelength. Hence it is also called incident photon to collected electron (IPCE), or external quantum efficiency (EQE) measurement. IPCE is given as... 

Incident Photon-to-Current Efficiency (IPCE)/External Quantum Efficiency (EQE)... 

The first application of discotic liquid crystal to organic thin film solar cells is of a binary blend of liquid crystalline phthalocyanine (Pc) as p-type of semiconductor and non- mesogenic PTCDI derivative as n-type [45], where the active layer was not a BHJ type, but had a p-i-n junction (Fig. 8.11). The Pc layer was fabricated by spin-coating and heated up to the isotropic phase followed by cooling to obtain a spontaneously formed homeotoropic alignment on ITO-coated substrate. The n-type layer was deposited by sublimation on Pc layer and finally the counter A1 electrode was deposited in vacuo. The performance was shown simply as short circuit current, Isc = 0.4 mA cm , open circuit voltage, Vqc = 0.3 V and external quantum efficiency, EQE 0.5 %. 

Park et al. used Hansen solubility parameters and showed that non-halogenated solvent blends with the same Hansen parameters as o-DCB can be used to reach comparable device performance [53]. They mixed mesitylene (MS) with acetophenone (AP) in different ratios to match o-DCB Hansen parameters. Different mixtures of AP and MS were used with different ratios resulting in PCEs ranging from 1.5% (pure MS) to 3.38% (20 vol.% acetophenone) for PlHTPCsjBM cells with best external quantum efficiency (EQE) match with o-DCB. This has so far been... 

The external quantum efficiency (EQE) of polymer PVs based on exciton dissociation at a donor-acceptor interface is )/eqe = /a x >7ed x j/co Here, j/a is the absorption efficiency. The exciton diffusion efficiency, is the fraction of photogenerated... 

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