Jonas Malmström

Zn(O,S) buffer layers by atomic layer deposition in Cu(In,Ga)Se2 based thin film solar cells: Band alignment and sulfur gradient

Thin film solar cells with the structure sodalimeglass∕Mo∕Cu(In,Ga)Se2∕Zn(O,S)∕ZnO∕ZnO:Al are studied for varying thickness and sulfur content of the Zn(O,S) buffer layer. These Zn(O,S) layers were deposited by atomic layer deposition (ALD) at 120°C. Devices with no or small concentrations of sulfur in the buffer layer show low open-circuit voltages. This is explained by the cliff, or negative conduction-band offset (CBO), of −0.2eV measured by photoelectron spectroscopy (PES) and optical methods for the Cu(In,Ga)Se2 (CIGS)∕ZnO interface. Devices with ZnS buffer layers exhibit very low photocurrent. This is expected from the large positive CBO (spike) of 1.2eV measured for the CIGS∕ZnS interface. For devices with Zn(O,S) buffer layers, two different deposition recipes were found to yield devices with efficiencies equal to or above reference devices in which standard CdS buffer layers were used; ultrathin Zn(O,S) layers with S∕Zn ratios of 0.8–0.9, and Zn(O,S) layers of around 30nm with average S∕Zn ratios...

Back surface band gap gradings in Cu(In,Ga)Se2 solar cells

Abstract We fabricate and analyse Cu(In,Ga)Se 2 -based solar cells which have a graded band gap by an increased Ga content towards the Mo back contact. The open circuit voltage and the short circuit current strongly improve with the band gap grading. Electronic device analysis reveals that the open circuit voltage increase is directly related to the increased band gap energy at the back surface. We interpret the obtained results to a large extent as reduced back contact recombination by the introduction of an increased band gap close to the back contact.

Enhanced back reflectance and quantum efficiency in Cu(In,Ga)Se2 thin film solar cells with a ZrN back reflector

A reactively sputtered ZrN reflector layer on top of the conventional Mo back contact yields enhanced absorber/back contact reflectance in Cu(In,Ga)Se2 thin film solar cells. Improved long wavelength quantum efficiency is demonstrated with a ZrN reflector at a Cu(In,Ga)Se2 thickness of 0.5 μm. The optical gain with respect to a standard Mo back contact is initially offset by increased back contact recombination and contact resistance, but these electronic losses can be suppressed by Ga grading of the absorber or by inclusion of a contact layer of MoSe2. This allows for a significantly improved power conversion efficiency of devices with sub-micron Cu(In,Ga)Se2 thickness.

A study of the influence of the Ga content on the long-term stability of Cu(In, Ga)Se2 thin film solar cells

A study of the influence of the Ga content on the long-term stability of Cu(In,Ga)Se2 thin film solar cells

High voltage Cu(In,Ga)Se/sub 2/ devices with Ga-profiling fabricated using co-evaporation

The influence of bandgap profiling of Cu(In,Ga)Se/sub 2/ absorbers for thin film solar cells has been investigated. Profiles have been obtained by depositing CuGaSe/sub 2/ back surface layers in the beginning of the Cu(ln,Ga)Se/sub 2/ growth process. Two different concentrations of Ga was used for the nongraded part of the Cu(ln,Ga)Se/sub 2/ film corresponding to Ga/(Ga+In) ratios of 0.2 and 0.5. The interdiffusion of Ga and In was studied and it was found that, although substantial interdiffusion occurred, a back surface layer with a high Ga content remained as analyzed with SIMS and XRD. The main influence on the solar cell parameters, by widening of the bandgap towards the back contact using this Ga-rich back surface layer, was found to be an enhancement of the efficiency by improved voltage.

Stabilization of PACREL® by organotellurium compound

The addition of 0.17-0.50% of bis[4-(dimethylamino)phenyl] telluride to the thermoplastic elastomer PACREL(R) significantly improved tensile strength and elongation at break in unaged and oven-aged ...

Optical modeling and simulation of thin-film Cu(In,Ga)Se2 solar cells

Optical modeling and results of numerical simulation of thin-film Cu(In,Ga)Se2 solar cells are presented. Main features of the developed optical simulator SunShine are explained. An approach to model light scattering at rough interfaces in the solar cell is described. Two types of scattering parameters are used: haze and angular distribution function of scattered light. Simulation results - total reflectance, absorptance in CIGS absorber and carrier generation rate profile - are shown and verified for the solar cell with thin (d=360 nm) CIGS absorber