The power conversion efficiency of solar cells based on copper (I) oxide (Cu2 O) is enhanced by atomic layer deposition of a thin gallium oxide (Ga2 O3 ) layer. By improving band-alignment and passivating interface defects, the device exhibits an open-circuit voltage of 1.20 V and an efficiency of 3.97%, showing potential of over 7% efficiency.

Sodium incorporation into Cu2ZnSnSe4 (CZTSe) substantially improves the device efficiency by enhancing the open-circuit voltage (VOC) and fill factor. Sodium increases hole density, makes the acceptor shallower, shifts the Fermi level lower, and leads to higher built-in voltage and, consequently, higher VOC. Sodium reduces the concentration of certain deep recombination centers, which further benefits VOC. The increase of hole density and mobility enhances the CZTSe conductivity leading to higher fill factor. Sodium causes smaller depletion width, hence, lower short-circuit current. The minority-carrier lifetime decreases slightly after sodium is incorporated via the Mo-coated soda-lime glass, although adding NaF provides some amelioration.

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World-record power conversion efficiencies for Cu(In,Ga)Se2 (CIGS) solar cells have been achieved via a post-deposition treatment with alkaline metals, which increases the open-circuit voltage and fill factor. We explore the role of the potassium fluoride (KF) post-deposition treatment in CIGS by employing energy- and time-resolved photoluminescence spectroscopy and electrical characterization combined with numerical modeling. The bulk carrier lifetime is found to increase with post-deposition treatment from 255 ns to 388 ns, which is the longest charge carrier lifetime reported for CIGS, and within ∼40% of the radiative limit. We find evidence that the post-deposition treatment causes a decrease in the electronic potential fluctuations. These potential fluctuations have previously been shown to reduce the open-circuit voltage and the device efficiency in CIGS. Additionally, numerical simulations based on the measured carrier lifetimes and mobilities show a diffusion length of ∼10 μm, which is ∼4 times larger than the film thickness. Thus, carrier collection in the bulk is not a limiting factor for device efficiency. By considering differences in doping, bandgap, and potential fluctuations, we present a possible explanation for the voltage difference between KF-treated and untreated samples.

| www.nrel.gov Grover, S.; Li, J.V.; Young, D.L.; Stradins, P.; Branz, H.M. (2013). " Reformulation of Solar Cell Physics to Facilitate Experimental Separation of Recombination Pathways. " Applied Physics Letters (103: 9); pp. 093502-093502-5. Achievement NREL developed a characterization approach to analyze recombination occurring via different channels in a solar cell. Key Result NREL researchers obtained an equation for open-circuit voltage that depends on light intensity, temperature, and strength of recombination in different regions of a solar cell. Potential Impact Applying the new formula allows accurate modeling of changes in performance due to defect parameters, light intensity, and temperature. Heterojunction band-diagram for amorphous/crystalline silicon (a-Si/c-Si) solar cell. The labeled regions of potential recombination are the front and rear surfaces, interface, space-charge region, and quasi-neutral region.