Wide bandgap top cells above 1.8 eV for reliable silicon-based tandem solar cells

The next generation of commercial solar cells must deliver a lower levelized cost of energy than the incumbent, crystalline silicon. Yet silicon solar cells set a formidable challenge, with degradation as low as 0.5 %/year and record efficiency exceeding 27 %. Success against silicon thus demands a challenging combination of performance and reliability, a combination that no other technology has met at scale. This raises an interesting possibility for solar cell designs that take maximal advantage of the strengths of silicon solar cells, rather than directly compete. In this contribution we theoretically assess a less commonly considered solar cell architecture: a non-current-matched, four-terminal tandem that pairs high efficiency silicon solar cells with wide-bandgap top-cell absorbers above 1.8 eV. This design shifts a majority share of power conversion to the silicon bottom cell and thereby expands the range of top-cell materials that can deliver tandem efficiencies above 30 % while simultaneously improving resilience to top-cell degradation. These advantages depend on high silicon efficiency, yet if this is the case, the top-cell absorber is freed from having to meet a demanding combination of optical bandgap, electronic quality and reliability.