Frank Hergert

A New Mass Production Technology for High-Efficiency Thin-Film CIS-Absorber Formation

A new mass production technology for CIS-absorber formation yielding high-average module efficiencies is introduced. A novel custom-designed oven very successfully exploits the principle of forced convection during heating, CIS formation reaction, and cooling. Cu(In,Ga)(Se,S) 2 absorbers are formed by metal precursor deposition on soda lime glass followed by reaction in selenium/sulfur atmosphere. Processing is performed in a multiple-chamber equipment which handles corrosive, flammable, and toxic process gases from atmospheric pressure to vacuum at high durability. The substrates (size: 50 cm × 120 cm) are processed in batches up to 102 substrates, applying forced convection for very homogenous heat transfer and high heating and cooling rates. Multiple-chamber design and batch size yield high throughput at cycle times above 1 h. This approach combines the specific advantages of batch type and inline processing. An excellent average efficiency of 14.3% with a narrow distribution (+/-0.31%) and a peak efficiency of 15.1% is shown with this technology. Module characteristic distributions during pilot production are presented. Detailed layer analytics is discussed. This straightforward reliable mass production technology is a key for highest module performance and for upscaling. Module efficiencies of 17% can be reached, enabling production costs below 0.38 US

Design, preparation and performance of Cu(In, Ga)(S, Se) 2 /Zn(O, S)/ZnO:Al solar cells

/Wp in a projected GWp plant.

Sputtered Zn(O,S): a promising approach to dry inline fabrication of Cdfree CIGS modules

Junction formation by chemical bath deposition of CdS is a well established and robust process. To avoid the well known drawbacks of this approach, we propose to omit the CdS buffer layer and to directly sputter a modified window layer where Zn(O, S) is used instead of ZnO to improve the band line-up. This could result in completely dry in-line manufacturing of Cd-free modules using only proven deposition technologies. Key requisites for a new module structure are that the efficiency is not adversely affected and that the process is stable with a wide process window. For a first assessment, tests were carried out using absorbers from industrial production.

An experimentally supported model for the origin of charge transport barrier in Zn(O,S)/CIGSSe solar cells

Sputtering of Zn(O,S) has emerged as an alternative technology for establishing the pn-junction for Cd-free chalcopyrite-based solar cells. Compared to the chemical bath deposition of CdS, this technology promises dry in-line fabrication of Cd-free modules with reduced complexity and cost. We will review the milestones of its development from fundamental investigations to scaling-up on large area sputter coaters. Reactive sputtering from ZnS targets has been used to initially assess basic film properties over the whole range of compositions from ZnO to ZnS. Subsequently, the process has been simplified and brought closer to industrial application by switching to mixed ZnO/ZnS targets.

Dry vacuum buffers for industrial chalcopyrite absorbers from a sequential absorber process route

Zinc oxysulfide buffer layers with [O]:[S] of 1:0, 6:1, 4:1, 2:1, and 1:1 ratios were deposited by atomic layer deposition on Cu(In,Ga)(S,Se)2 absorbers and made into finished solar cells. We demonstrate using Time-Resolved Photoluminescence that the minority carrier lifetime of Zn(O,S) buffered solar cells is dependent on the sulfur content of the buffer layer. τ1 for devices with [O]:[S] of 1:0–4:1 are <10 ns, indicating efficient charge separation in devices with low sulfur content. An additional τ2 is observed for relaxed devices with [O]:[S] of 2:1 and both relaxed and light soaked devices with [O]:[S] of 1:1. Corroborated with one-dimensional electronic band structure simulation results, we attribute this additional decay lifetime to radiative recombination in the absorber due to excessive acceptor-type defects in sulfur-rich Zn(O,S) buffer layer that causes a buildup in interface-barrier for charge transport. A light soaking step shortens the carrier lifetime for the moderately sulfur-rich 2:1 devi...

ILGAR In2S3 buffer layers for Cd‐free Cu(In,Ga)(S,Se)2 solar cells with certified efficiencies above 16%

First results are presented for chalcopyrite solar cells with Cd-free dry buffer layers prepared by two different vacuum deposition techniques on sequentially processed Cu(In, Ga)(S, Se)2 absorbers. The deposition techniques are namely thermal evaporation of In2S3 compound powder and the reactive sputtering of Zn(O, S) layers. Both approaches are suitable for an in-line assembly into an industrial production line. The influence of the variation of process parameters such as buffer layer thickness and annealing time on current-voltage characteristics and quantum efficiency is shown. Best cell results exceed 14% conversion efficiency for the In2S3 approach (>11% for the Zn(O, S) approach) which is comparable but slightly less than the standard CdS reference cells (>15%).