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 m2 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 ∼13, ∼7, ∼2, and ∼1 months, respectively. On an impacts per kW h 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 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.
- This article is part of the themed collection: 2017 Energy and Environmental Science HOT articles