Environmental analysis of perovskites and other relevant solar cell technologies in a tandem configuration

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 assessment model to evaluate the environmental impacts, primary energy demand (PED), and energy payback time (EPBT) of four integrated two-terminal tandem solar cells composed of either Si bottom and lead-based perovskite (PKPb) top cells (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). 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 m(2) area of a cell were largely determined by the bottom cell impacts and ranged from 50% (CZTS/PKPb) to 120% of those 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 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 similar to 13, similar to 7, similar to 2, and similar to 1 months, respectively. On an impacts per kW h of Si basis the environmental impacts of all the devices were much higher (up to similar 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 current low PCE (21%) and short lifetime (5 years) assumptions, it can outperform Si if its lifetime and PCE reach 16 years and 30%, respectively. Among the configurations considered, the PKSn, Pb/PKPb structure has the potential to be the most environmentally friendly technology.