Lab Manager: Diego Alonso Álvarez
Boosting the performance of solar cells beyond their current limitations require a profound understanding of the electro-optical properties and carrier dynamics of new, exciting materials and solar cell designs. Among the materials that are often of interests for us are quantum nanostructures (wells, wires and dots), novel alloys (dillute nitrides and bismides, SiGeSn, perovskites) and luminescent molecules and nanoparticles.
The QPV spectroscopy lab is where we perform most of the analysis of these materials from the fundamental point of view. The most basic technique available is photoluminescence spectroscopy, with a laser exciting carriers in the material and a spectrometer analysing the emitted light, but the possibilities are much broader due to the flexibility of the setup. Techniques that are standard in our lab or can be implemented as needed are:
• Photoluminescence (PL)
• Electroluminescence (EL)
• Time resolved photoluminescence (TRPL)
• Photoluminescence excitation (PLE)
• Carrier collection efficiency (CCE)
Most of them can be performed as a function of several parameters such as temperature, excitation intensity, excitation wavelength or applied voltage. This basic setups can be easily modified to perform pump-probe experiments with two co-linear laser beams, polarisation sensitive PL, PL- and EL-based IV curves, EL imaging, etc.
The main pieces of equipment in our lab are:
• Millenia V Nd:YAG laser - 532 nm, 5W, continuum.
• Spectra Physics Tunable Ti:Sapphire laser - 700 to 1100 nm, up to 2 W (wavelength dependent), continuum.
• Picoquant lasers - 485 nm and 780 nm, pulsed (up to 80 MHz)
• Thorlabs laser diodes - Several wavelengths, continuum + pulsed (~kHz range)
• Halogen lamp + Bentham monochromator - Tunable "weak" source, temperature ~2800K, continuum
• Newport Silicon photodiode (up to 1100 nm), steady state
• Priceton Instruments InGaAs array (up to1500 nm), steady state, nitrogen cooled
• Extended InGaAs photodiode (visible to 2200 nm), steady state, nitrogen cooled
• Hamamatsu InGaAsP PMT (940-1500 nm), steady state + single photon counting, peltier cooled
• BH GaAs PMT (UV to 880 nm), steady state + single photon counting, peltier cooled
• Silicon APD (up to 1100 nm), single photon counting
• Ocean Optics HR400 fast spectrometer (300-1000 nm), steady state
• Priceton Instruments Acton 2500i spectrometer
• Close circuit Helium cryostat + temperature controller (11 K -340 K)
• Keithley Source-Meter unit
• Thorlabs UV-VIS-NIR camera
• Function generators
• Mechanical chopper
Recent papers with measurements taken in this lab:
 D. Alonso-Álvarez, T. Thomas, M. Führer, N. P. Hylton, N. J. Ekins-Daukes, D. Lackner, S. P. Philipps, a. W. Bett, H. Sodabanlu, H. Fujii, K. Watanabe, M. Sugiyama, L. Nasi, and M. Campanini, “InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells,” Appl. Phys. Lett., vol. 105, no. 8, p. 083124, Aug. 2014.
To book use of the spectroscopy lab please fill in the booking form here, or comtact the lab manager for further details.
Quantum efficiency lab
Quantum efficiency lab
Lab Manager: Tom Wilson & José Videira
Our quantum efficiency lab has equipment for performing several common electrical and optical tests of solar cell devices.
We can perform several varieties of quantum efficiency measurements in the wavelength range 300nm – 1800nm using monochromated white light and calibrated detectors. We have a flexible set-up that allows for the measurement of both single and multi-junction cells of different cell sizes – notable achievements have included measurement of the quantum efficiency of a 6 junction solar cell and measurement of the effect of nano-particle arrays that cover an area on the scale of hundreds of micrometers.
We can also perform the following electrical device tests:
• External/internal quantum efficiency
• Dark IV
• Light IV with range of illumination including class A solar simulator
• Capacitance & DLTS measurements
• Electroluminescence imaging
These measurements can also be performed as a function of temperature.
Recent papers with measurements taken in this lab:
T. Thomas, M. Führer, D. A. Alvarez, N. Ekins-daukes, K. H. Tan, W. K. Loke, S. F. Yoon, and A. Johnson, “GaNAsSb 1-eV solar cells for use in lattice-matched multi-junction architectures,” Proc. 40th IEEE Photovolt. Spec. Conf., pp. 550–553, 2014.
In the Quantum Photovoltaics Group we have always developed theory and modelling alongside the experimental work in order to get a better understanding of the physical processes involved in new solar cell concepts. While we have often used existing software - either freeware (PC1D, SMARTS …) or commercial (Nextnano, COMSOL, PVsys…) - we have also developed our own homemade tools. This not only provided efficient programs to solve the specific topics we were interested, but also taught us a lot of things about how to tackle real problems from the computing perspective.
Solcore was born as a modular set of tools, written entirely in Python 3, to address some of the task we had to solve more often, such as fitting dark IV curves or luminescence decays. With time, however, it has evolved as a complete semiconductor solver able of modelling the optical and electrical properties of a wide range of solar cells, from quantum well devices to multi-junction solar cells. Some of the features of Solcore are:
- k•p band structure solver including strain
- 1D arbitrary potential Schrödinger equation solver
- Bulk and QW absorption profile calculator
- Coupled Drift-Diffusion - Poisson equations solver
- Spectral irradiance model and database
- Multi-junction QE and IV calculator
Unfortunately, Solcore is just for internal use and therefore it is not available for download.
Recent papers using Solcore capabilities:
 T. Thomas, A. Mellor, N. P. Hylton, M. Führer, D. Alonso-Álvarez, A. Braun, N. J. Ekins-Daukes, J. P. R. David, and S. J. Sweeney, “Requirements for a GaAsBi 1 eV sub-cell in a GaAs-based multi-junction solar cell,” Semicond. Sci. Technol., vol. 30, no. 9, p. 094010, 2015.
 D. Alonso-álvarez, M. Führer, T. Thomas, and N. Ekins-daukes, “Elements of modelling and design of multi-quantum well solar cells,” Proc. 40th IEEE Photovolt. Spec. Conf., pp. 0–5, 2014.
 T. Thomas, M. Führer, D. A. Alvarez, N. Ekins-daukes, K. H. Tan, W. K. Loke, S. F. Yoon, and A. Johnson, “GaNAsSb 1-eV solar cells for use in lattice-matched multi-junction architectures,” Proc. 40th IEEE Photovolt. Spec. Conf., pp. 550–553, 2014.
 M. Führer, D. Farrell, and N. Ekins-Daukes, “CPV modelling with Solcore: An extensible modelling framework for the rapid computational simulation and evaluation of solar cell designs and concepts,” AIP Conf. Proc., vol. 1556, no. 1, pp. 34–37, Sep. 2013.
PVtrace was originally written to simulate luminescent solar concentrators during Dr. Daniel Farrel PhD studies at the QPV group. However it has grown into a much more powerful tool, capable of optical ray tracing complicated structures, and the collection of statistical data to enable characterisation of optics useful for photovoltaics and solar energy conversion. PVtrace is written entirely in Python. Using the numpy library. This was chosen to emphasis rapid development, learning and collaboration rather than speed of execution.
If you use PVtrace please use the following citation,
Daniel J Farrell, "PVtrace : optical ray tracing for photovoltaic devices and luminescent materials", http://dx.doi.org/10.5281/zenodo.12820
Overview of features:
- Constructive Solid Geometry
- Generalised 3D ray intersections (ray optics):
- ray-CSG object
- Arbitrary 3D object transformations:
- scaling and skewing
- Photon path visualiser
- Statistical collection of photonic properties:
- Automatic Fresnel reflection and refraction
- Sampling from statistical distributions:
- optical absorption coefficient
- emission spectrum
- wavelength and angular reflectivity