Ilke Celik1 3 Zhaoning Song1 2 Adam Phillips2 Randy Ellingson2 Yanfa Yan2 Michael Heben2 Defne Apul3

1, University of Toledo, Toledo, Ohio, United States
3, University of Toledo, Toledo, Ohio, United States
2, University of Toledo, Toledo, Ohio, United States

Future high performance PV devices are expected to be tandem cells consisting of a low-bandgap bottom cell and a high-bandgap top cell. In this study, we developed a cradle-to-end of use life cycle inventory to evaluate the environmental impacts, primary energy demand (PED), and energy payback time (EPBT) for four integrated two-terminal tandem solar cells comprised of either Si bottom and lead-based perovskite (PKPb) top cell (Si/PKPb), copper indium gallium selenide (CIGS) and PKPb (CIGS/PKPb), copper zinc tin selenide (CZTS) and PKPb (CZTS/PKPb), or tin-lead based perovskite (PKSn,Pb) and PKPb (PKSn,Pb/PKPb). The environmental impacts from single junction Si solar cells were used as a reference point to interpret the results. We found that the environmental impacts for a 1 m2 area of a cell was largely determined by the bottom cell impacts and ranged from 50 % (CZTS/PKPb) to 120 % of a Si cell. The ITO layer used in Si/PKPb, CZTS/PKPb, and PKSn,Pb/PKPb is the most impactful after the Si and CIGS absorbers, and contributed up to 70 % (in PKSn,Pb/PKPb) of the total impacts for these tandem PVs. Manufacturing a single two-terminal device was found to be a more environmentally friendly option than manufacturing of the two constituent single-junction cells, and can reduce the environmental impacts by 30 % due to the exclusion of extra glass, encapsulation, front contact and back contact layers. PED analysis indicated that PKSn,Pb/PKPb manufacturing has the least energy-intensive processing, and the EPBTs of Si/PKPb, CIGS/PKPb, CZTS/PKPb, and PKSn,Pb/PKPb tandems were found to be ~13, ~7, ~2, and ~1 months, respectively. On an impacts/kWh of Si basis the environmental impacts of all the devices were much higher (up to ~10 times). These results can be attributed to the low photoconversion efficiency (PCE) and short lifetime that were assumed. While PKSn,Pb/PKPb has higher impacts than Si based on today’s low PCE (21 %) and short lifetime (5 yr) assumptions, it can outperform Si if its lifetime and PCE reach 16 yr and PCE of 30%. Of the configuration considered, the PKSn,Pb/PKPb structure is the most environmentally friendly technology.