We report a new record total-area efficiency of 19Á9% for CuInGaSe 2 -based thin-film solar cells. Improved performance is due to higher fill factor. The device was made by three-stage co-evaporation with a modified surface termination. Growth conditions, device analysis, and basic film characterization are presented.

We report a new state of the art in thin‐film polycrystalline Cu(In,Ga)Se2‐based solar cells with the attainment of energy conversion efficiencies of 19·5%. An analysis of the performance of Cu(In,Ga)Se2 solar cells in terms of some absorber properties and other derived diode parameters is presented. The analysis reveals that the highest‐performance cells can be associated with absorber bandgap values of ∼1·14 eV, resulting in devices with the lowest values of diode saturation current density (∼3×10−8 mA/cm2) and diode quality factors in the range 1·30 < A < 1·35. The data presented also support arguments of a reduced space charge region recombination as the reason for the improvement in the performance of such devices. In addition, a discussion is presented regarding the dependence of performance on energy bandgap, with an emphasis on wide‐bandgap Cu(In,Ga)Se2 materials and views toward improving efficiency to > 1;20% in thin‐film polycrystalline Cu(In,Ga)Se2 solar cells. Published in 2005 John Wiley & Sons, Ltd.

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We report on improvements to the energy conversion efficiency of wide bandgap (Eg > 1.2 eV) solar cells on the basis of CuIn1−xGaxSe2. Historically, attaining high efficiency (>16%) from these types of compound semiconductor thin films has been difficult. Nevertheless, by using (a) the alkaline‐containing high‐temperature EtaMax glass substrates from Schott AG, (b) elevated substrate temperatures of 600–650 °C, and (c) high vacuum evaporation from elemental sources following National Renewable Energy Laboratory's three‐stage process, we have been able to improve the performance of wider bandgap solar cells with 1.2 < Eg < 1.45 eV. The current density–voltage (J–V) data we present includes efficiencies >18% for absorber bandgaps of ~1.30 eV and efficiencies of ~16% for bandgaps up to ~1.45 eV. In comparing J–V parameters in similar materials, we establish gains in the open‐circuit voltage and, to a lesser degree, the fill factor value, as the reason for the improved performance. The higher voltages seen in these wide gap materials grown at high substrate temperatures are due to reduced recombination. We establish the existence of random and discrete grains within the CIGS absorbers that yield limited or no generation/collection of minority carriers. We also show that interfacial recombination is the main mechanism limiting additional enhancements to open‐circuit voltage and therefore performance. Solar cell results, absorber materials characterization, and experimental details and discussion are presented. Copyright © 2012 John Wiley & Sons, Ltd.

The growth and characterization of Cu(ln,Oa)Se, polycrystalline thin films under the presence of thin-MF (M=Na, K, Cs) precursor layers is presented. Some electrical, structural, and electronic absorber properties due to the presence of such Group la impurities are quantified along with their influence in device performance. We present a growth model for the role of Na in Cu(ln,Ga)Se, that attributes the enhancemeiits in electrical conductivity and photovoltaic device performance to the extinction of a finite number of donor states (i.e., I n , ) at the bulk and grain-boundary regions.