Photoluminescence Analysis of Electron Damage for Minority Carrier Diffusion Length in GaInP/GaAs/Ge Triple-Junction Solar Cells

Photoluminescence（PL） measurements are carried out to investigate the degradation of GaInP top cell and GaAs middle cell for GaInP/GaAs/Ge triple-junction solar cells irradiated with 1.0, 1.8 and 11.5 MeV electrons with fluences ranging up to 3 × 10^15, 1 × 10^15 and 3 × 10^14 cm^-2, respectively. The degradation rates of PL intensity increase with the electron fluence and energy. Furthermore, the damage coefficient of minority carrier diffusion length is estimated by the PL radiative efficiency. The damage coefficient increases with the electron energy. The relation of damage coefficient to electron energy is discussed with the non-ionizing energy loss（NIEL）, which shows a quadratic dependence between damage coefficient and NIEL.

Photoelectrochemical evaluation of SILAR-deposited nanoporous BiVO4 photoanodes for solar-driven water splitting

We report a photoelectrochemical investigation of BiVO4 photoanodes prepared by successive ionic layer adsorption and reaction(SILAR),a facile method that yields uniform nanoporous films.After characterization of the phase,morphology,composition,and optical properties of the prepared films,the efficiencies of charge separation(ηsep)and water oxidation(ηox)in solar water splitting cells employing these photoanodes were estimated following a previously reported procedure.Unexpected wavelength and illumination direction dependencies were discovered in the derived efficiencies,casting doubt on the validity of the analysis.An alternative approach using a diffusion–reaction model that explicitly considers the efficiency of electron collection resolved the discrepancies and explained the illumination direction dependence of the photocurrent.Electron diffusion lengths(Ln)of 0.45μm and 0.55μm were derived for pristine and cobalt phosphate(Co-Pi)modified BiVO4,respectively,which are much shorter than the film thickness of^2.1μm.The Co-Pi treatment also increasedηoxfrom 0.86 to^1,which is the main reason for the overall performance enhancement caused by adding Co-Pi.These findings suggest that there is little scope for improving the performance of SILAR-deposited BiVO4 photoanodes by further catalyzing water oxidation,but enhanced performance is achievable if electron transport can be improved.

Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage （SPV） curve before activation and the spectral response curve （SRC） after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability （SEP） can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future.