The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck. Silicon/perovskite tandem solar cells are a solution, which is attracting much attention. While silicon/perovskite tandem cells in 2-terminal and 4-terminal configurations are well documented, the three-terminal concept is still in its infancy. It has significant advantages under low light intensities as opposed to concentrated sunlight, which is the critical factor in designing tandem solar cells for low-cost terrestrial applications. This study presents novel studies of the sub-cell performance of the first three-terminal perovskite/silicon selective band offset barrier tandem solar cells fabricated in an ongoing research project. This study focuses on short circuit current and operating voltages of the sub-cells under light intensities of one sun and below. Lifetime studies show that the perovskite bulk carrier lifetime is insensitive to illumination, while the silicon cell's lifetime decreases with decreasing light intensity. The combination of perovskite and silicon in the 3T perovskite-silicon tandem therefore reduces the sensitivity of VOC to light intensity and maintains a relatively higher VOC down to low light intensities, whereas silicon single-junction cells show a marked decrease. This technological advantage is proposed as a novel advantage of three-terminal perovkite/silicon solar cells for low light intensities of one sun or less. ... Read more

The perovskite solar cell (PSC) is one of the most dramatic inventions in the field of photovoltaics in the last half century. The device has rapidly risen from a few percent to efficiencies of over 24% [1] in little over a decade. This rapid development is due in part to the wide family of perovskite absorber and of electron and hole tranport materials available which yields great flexibility. The flip-side of this profusion of materials is the challenge in establishing achievable performance potential of real devices. This paper therefore presents a study of the perovskite solar cell materials and applies numerical modelling techniques to evaluate the most promising materials combinations and their efficiency potential. The preliminary device structure is a simple three-layer design consisting of hole transport layer, perovskite aborber, and electron transport layer, on a glass substrate in a p-i-n or “inverted” configuration. A range of materials for these layers is compared and contrasted for this polarity. The structure is then generalised to more complex designs featuring protective buffer layers which prevent damage to the perovskite absorber layer, and two dimensional perovkite layers which have been shown to improve perovskite material stability. The realistic efficiency potential of the materials considered is discused in the context of the common radiative efficiency limit. The study concludes by recommending promising materials combinations for high efficiency PSC compatible with cost effective indutrial fabrication method for single juntion and for multijunction device design in the context of H2020 Solar-ERANET project BOBTANDEM [2]. This work contributes to define efficiencies achievable in this materials systems, both for single junction and multijunction devices which are of great societal interet for cost effective renewable power generation. ... Read more

The most successful high efficiency design, and one of the oldest, is the multi-junction solar cell. There are a range of multijunction solar cell terminal configurations, the specificities of which are reviewed, concluding with noting the increased attention being given to three terminal designs. This introduces a new device design which is the Three Terminal Selective Band Offset Barrier tandem solar cell. The physical operation of this new device is examined, and embodiments in prototype materials relying on materials properties from the literature. We present projected performance evaluated by two dimensional numerical modelling. Identifying shortcomings on two fronts of materials and optical properties of the multilayer stack, we describe theoretical progress in optimising these properties via ab initio materials modelling and combined ray and wave optics. This theoretical context introduces the experimental results obtained in the first year of the project. This consists of successful integration of the selective band offset barrier on a suitably modified IBC structure using prototype materials previously reported. This paper thereby presents detailed analysis of the three terminal selective band offset barrier tandem solar cell, and announces the first experimentally fabricated three terminal selective band offset barrier solar cells, together with preliminary conclusions of experimental characterisation which is underway. . ... Read more