Advanced Device Concepts for Next-Generation Photovoltaics

Evolution in device architectures have been central to the performance enhancements in all photovoltaic (PV) technologies. For silicon PV cells, they started as p-n junctions originating from the early p and n-doping studies in Bell Labs, USA, in the 1950s and have progressed to passivated interfaces with charge selective "heterojunctions" sandwiching homogeneously doped single crystal wafers. For metal halide perovskites, the early PV embodiments comprised perovskite nanocrystals "sensitizing" mesoporous TiO2 and have progressed to solid-perovskite absorber layers sandwiched between planar heterojunctions with increasingly well passivated interfaces. However, even a perfectly-passivated solar cell fabricated from a single solar absorber material has its limitations, with theoretical maximum solar-to-electric power conversion efficiencies topping out at 30%. The most popular route to circumvent these limitations is to create "multi-junction" or tandem solar cells, where more than one solar absorber material and device are stacked on top of each other, which leads to a theorised increase in efficiency to 45% for two junctions and over 50% for three junctions. The top runner for tandem cells is combining metal-halide perovskites with silicon, which have already demonstrated over 31% efficiency, and one of our partners, Oxford PV, is ramping up production of the first perovskite-on-silicon tandem technology. However, tandem cells are not the final word in PV efficiency.

Our ambition is to carry out multidisciplinary research, via inter-linked work streams, that will explore and conceive new photovoltaic device concepts and paradigms, enabling the next major step-change in photovoltaic efficiency.

We base our vision on two key questions; what do we predict to be the next game-changing transformation to PV technology? and what fundamental science and technical advances do we need to develop now, in order to deliver such a paradigm shift?

We target 4 device concepts;
* CONCENTRATOR PV, which operate under concentrated sun light to result in a 20 to 30% relative increase in power conversion efficiency as compared to "1-sun" operation technologies;
* QUANTUM CUTTING, for which rare-earth doping of novel halide semiconductors can result in the generation of two low-energy photons for every high-energy photon absorbed, boosting the photocurrent generation in a PV device through photon-multiplication;
* HOT-CARRIER COLLECTION, where carrier cooling losses are overcome by selectively extracting hot charge from a solar cell, boosting the theoretical efficiency limit all the way to 66%;
* and a novel idea of a "PHOTON-TRANSPORT" cell, designed so that the majority of charges are transported to charge collection interfaces via photons, with the elimination of minority carriers from the bulk of the absorber negating internal recombination losses and enabling PV cells to reach their theoretical "radiative" limit.

The PV absorber materials will be based on metal-halide perovskites, silicon, and novel low-band-gap chalcogenide-halide semiconductors designed and discovered in this project. Addressing these future advanced concepts through a holistic approach will enable us to make the first key scientific discoveries and important major technical advances in what will become the next generation of PV technologies for beyond 2030.