Bifacial (Ag,Cu)(In,Ga)Se ₂ Mini‐Modules With Transparent ITiO Back Contacts: Performance Analysis and Effects of RbF Treatment

Bifacial (Ag,Cu)(In,Ga)Se ₂ (ACIGS) mini‐module prototypes employing a high‐mobility ITiO transparent back contact are presented. A champion front‐side efficiency of 13.5% (14.3% initially, prior to sample shipment) is achieved for a 7.14 cm ² aperture‐area module without using anti‐reflection coatings (ARC), with a bifaciality factor of 76% enabled by the excellent optical transparency of the ITiO film. To boost the open circuit voltage, the absorber is subjected to an RbF post‐deposition treatment (PDT). Although the RbF‐PDT initially introduces a charge‐carrier transport barrier that reduces the fill factor, this penalty is completely eliminated by a heat‐light soaking (HLS) treatment. The HLS treatment, however, slightly reduces the rear‐side collection efficiency due to a narrowing of the space‐charge region. The primary cell‐to‐module efficiency loss of about 2% points is attributed to a fill‐factor reduction from ≈75% to ≈67%. Reference cells using an ITO back contact and a thinner front electrode, fabricated in the same absorber depositions as the corresponding modules, reach efficiencies up to 18% (w/o ARC). Finally, an all‐laser‐scribed monolithic series interconnection is demonstrated alongside an alternative approach in which the P3 isolation line is defined by a lithography‐based process.