A bottom-up cost analysis of silicon–perovskite tandem photovoltaics

Stacking two photovoltaic (PV) cells to form a tandem structure can improve the efficiency of PV modules, and if achieved at sufficiently low cost, could dominate the PV market in the future. Rapid progress in silicon–perovskite tandem (SPT) cell efficiency has been made, so cost modelling is becoming important in analysing the commercial attractiveness of this approach. While previous cost modelling assumed idealised production processes, this work focuses first on six demonstrated SPT sequences using both homojunction and heterojunction bottom silicon cells, analysed in detail using a bottom-up cost and uncertainty model and then compared with other reported SPT high-efficiency cells. This identifies cost barriers in the perovskite cell, including high-cost hole transport material (HTM) and electron transport layer (ETL) materials such as (2,2^′,7,7^′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9^′-spirobifluorene [SPIRO] and [6,6]-phenyl-C61-butyric acid methyl ester [PCBM]), and the use of spin coating which has a high wastage rate. Once these cost issues are solved, the silicon cell cost becomes important, and the use of lower cost homojunction cells with p-type wafers can further reduce costs. A hypothetical medium term low-cost sequence that combines the lowest cost parts of the analysed sequences and an improved perovskite deposition process has a projected likely cost of $1.50/cell, which if combined with 25% efficiency would give a favourable levelised cost of electricity (LCOE) compared with industry standard c-Si cells. This analysis guides research directions to address cost issues in parallel with higher efficiencies in this technology area.