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.