630
A. Jariwala et al.
along with the thickness of SCR in the absorber region by using the small signal
approximation model presented by them.
5.5 Organic Materials and PV Devices
The SPS has also been emerging as one of the promising characterization techniques
to probe the organic materials, devices, and processes. [97, 104, 105, 116, 117].
Moons et al. [118] employed the Kelvin probe method based SPS to determine the
work function of solid layers of the hole conductors diketopyrrolopyrrole (DPP) and
dithioketopyrrolopyrle (DTPP) on SnO 2 :F. Using the work function thus obtained,
they reported the determination of the width of the space charge layer at the interface
and the total voltage drop over the organic layer were deduced. They could also
demonstrate two photoactive areas in their structure, one at the air/DTPP interface
and one at the DTPP/SnO 2 :F interface, was demonstrated by measuring the surface
photovoltage (SPV) spectra under front and back side illumination, and their dependence on the layer thickness. Using these informations, they successfully configured
the energy band structure for entire device. L. N. S. Murthy et al. [119] carried out
extensive studies on fullerene based organic photovoltaics (OPV) with both, conventional as well as inverted architecture. They used the SPS measurements to study
the charge transfer mechanism from the active layer to the bottom of transport layer.
Using the SPS they could show that the SPS signals and spectral shape depend are
strong function of donor concentration in the conventional architecture. However
this dependence fades out in the inverted architecture.
5.6 Low-Dimensional Structures
Just like their bulk counterparts, SPS is an effective characterization tool for characterization of quantum wells and other low-dimensional heterostructures as well
[34, 35, 120, 121]. The SPS offers several advantages, particularly for these lowdimensional semiconductor structures. For instance, the method can easily be applied
to buried interfaces, heterostructures, thin films, nano-structured materials and
devices, and all such applications, where it is not possible to carry out the routine
transmission or absorption spectroscopy. Further, it does not require tedious sample
preparation or junction/contact deposition, etc. and. These advantages make it an
attractive characterization tool to probe to energy band structures of the nano- and
other low-dimensional structures. For example, Zhao et al. [122] employed SPS
to investigate the photochemistry of a mercaptoethanol-ligated CdSe quantum dot,
which find its applications in quantum dots solar cells. Shearer et al. have investigated
charge separation across WSe 2 –MoS 2 lateral heterostructures by SPV in combination
with Kelvin Probe microscopy [123]. Melo et al. have probed photopotential across a
A. Jariwala et al.
along with the thickness of SCR in the absorber region by using the small signal
approximation model presented by them.
5.5 Organic Materials and PV Devices
The SPS has also been emerging as one of the promising characterization techniques
to probe the organic materials, devices, and processes. [97, 104, 105, 116, 117].
Moons et al. [118] employed the Kelvin probe method based SPS to determine the
work function of solid layers of the hole conductors diketopyrrolopyrrole (DPP) and
dithioketopyrrolopyrle (DTPP) on SnO 2 :F. Using the work function thus obtained,
they reported the determination of the width of the space charge layer at the interface
and the total voltage drop over the organic layer were deduced. They could also
demonstrate two photoactive areas in their structure, one at the air/DTPP interface
and one at the DTPP/SnO 2 :F interface, was demonstrated by measuring the surface
photovoltage (SPV) spectra under front and back side illumination, and their dependence on the layer thickness. Using these informations, they successfully configured
the energy band structure for entire device. L. N. S. Murthy et al. [119] carried out
extensive studies on fullerene based organic photovoltaics (OPV) with both, conventional as well as inverted architecture. They used the SPS measurements to study
the charge transfer mechanism from the active layer to the bottom of transport layer.
Using the SPS they could show that the SPS signals and spectral shape depend are
strong function of donor concentration in the conventional architecture. However
this dependence fades out in the inverted architecture.
5.6 Low-Dimensional Structures
Just like their bulk counterparts, SPS is an effective characterization tool for characterization of quantum wells and other low-dimensional heterostructures as well
[34, 35, 120, 121]. The SPS offers several advantages, particularly for these lowdimensional semiconductor structures. For instance, the method can easily be applied
to buried interfaces, heterostructures, thin films, nano-structured materials and
devices, and all such applications, where it is not possible to carry out the routine
transmission or absorption spectroscopy. Further, it does not require tedious sample
preparation or junction/contact deposition, etc. and. These advantages make it an
attractive characterization tool to probe to energy band structures of the nano- and
other low-dimensional structures. For example, Zhao et al. [122] employed SPS
to investigate the photochemistry of a mercaptoethanol-ligated CdSe quantum dot,
which find its applications in quantum dots solar cells. Shearer et al. have investigated
charge separation across WSe 2 –MoS 2 lateral heterostructures by SPV in combination
with Kelvin Probe microscopy [123]. Melo et al. have probed photopotential across a