Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency

Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. State-of-the-art monolithic two-terminal perovskite/silicon tandem devices have so far featured silicon bottom cells that are polished on their front side to be compatible with the perovskite fabrication process. This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping. To tackle this issue, we developed a top cell deposition process that achieves the conformal growth of multiple compounds with controlled optoelectronic properties directly on the micrometre-sized pyramids of textured monocrystalline silicon. Tandem devices featuring a silicon heterojunction cell and a nanocrystalline silicon recombination junction demonstrate a certified steady-state efficiency of 25.2%. Our optical design yields a current density of 19.5 mA cm−2 thanks to the silicon pyramidal texture and suggests a path for the realization of 30% monolithic

Hole Mobility of a Liquid Organic Semiconductor

The first detailed study of charge transport through a liquid organic semiconductor (LOS) is reported with the goal of elucidating the effects of molecular motion on charge transport through molecular liquids. Using a liquid, silyl ether-substituted triarylamine, hole transport mobilities were obtained over a wide range of temperatures above the glass transition temperature of the material. Analysis of this data reveals that molecular motion(s) have a negligible effect on macroscopic charge transport through a molecular liquid. The results strongly resemble transport behavior found in conventional, disordered solids and suggest that silyl ether-substituted LOSs may be good candidates for integration into electronic devices, by those who are familiar with the application of traditional triarylamines, where their unique physical state can or could be exploited

Palliating the efficiency loss due to shunting in perovskite/silicon tandem solar cells through modifying the resistive properties of the recombination junction

As the efficiency of commercial crystalline silicon solar cells approaches its maximum theoretical value, tandem architectures are becoming increasingly popular to continue the push to higher photovoltaic performances. Thin-film materials are particularly interesting partners for silicon wafers due to their potential cost effectiveness and ease of fabrication. However, in large scale thin-film coatings, particularly for perovskite materials, avoiding the formation of point shunts is a challenge. This study investigates the sensitivity of perovskite/silicon tandems to such shunts and whether or not optimising the lateral and transverse resistances of the recombination junction can reduce the negative effects of these defects. To do so, the inhomogeneous characteristic of shunts is reproduced by modelling tandem cells with an array of scaled equivalent circuit elements connected in parallel. It is shown that by optimising the resistive properties of the interconnection, there can be an important quenching effect on shunts present in the top cell, resulting in a significant increase in the overall cell efficiency at STC and under low light conditions. These findings give a clear pathway on how to bridge the efficiency gap between small laboratory cells, which can be selected shunt free, and industry scale devices, which are more prone to localised shunting

Siliconized Triarylamines As Redox Mediator in Dye-Sensitized Solar Cells

A new class of triarylamine compound functionalized with bulky triisopropylsilyl ether (−OTIPS) groups is used as a hole transport material in dye-sensitized solar cells (DSSCs). Using both optical and photoelectrochemical techniques, we compared the performance of this compound with that of a parent compound containing methyl ethers as well as the conventional I₃^–/I^– redox couple. DSSCs fabricated with the triisopropylsilyl ether-substituted triarylamine exhibited high open circuit potentials (<i>V</i>_oc > 0.9 V on average) and efficiencies of up to 1.9%. However, cells fabricated with triarylamine containing methyl ethers performed very poorly, pointing to the importance of −OTIPS in the overall performance of this material

Perovskite/Perovskite/Silicon Monolithic Triple-Junction Solar Cells with a Fully Textured Design

High efficiency triple-junction solar cells are currently made of III−V semiconductors using expensive deposition methods. Perovskite/perovskite/silicon monolithic triple-junction solar cells could be a lower-cost alternative as no epitaxial growth is required. We demonstrate here that such devices can be realized using textured crystalline silicon bottom cells for optimal light management. By changing the perovskite absorbers composition and recombination junctions to make them compatible with the subsequent fabrication steps, triple-junction devices with open-circuit voltage up to 2.69 V are realized. To illustrate the applicability of the technology, we show how the band gaps and thicknesses of the top and middle cells can be modified to approach current-matching conditions. The limitations of these devices are discussed, as well as strategies to make them competitive with III−V triple-junction cells. The concepts presented here are a first step toward high-efficiency, high-voltage, and low-cost triple-junction photovoltaics

Low-Temperature Screen-Printed Metallization for the Scale-Up of Two-Terminal Perovskite-Silicon Tandems

Tandem photovoltaic devices based on perovskite and crystalline silicon (PK/c-Si) absorbers have the potential to push commercial silicon single junction devices beyond their current efficiency limit. However, their scale-up to industrially relevant sizes is largely limited by current fabrication methods which rely on evaporated metallization of the front contact instead of industry standard screen-printed silver grids. To tackle this challenge, we demonstrate how a low-temperature silver paste applied by a screen-printing process can be used for the front metal grid of two-terminal perovskite-silicon tandem structures. Small-area tandem devices with such printed front metallization show minimal thermal degradation when annealed up to 140 degrees C in air, resulting in silver bulk resistivity of <1 x 10(-5) Omega.cm. This printed metallization is then exploited in the fabrication of large area PK/c-Si tandems to achieve a steady-state efficiency of 22.6% over an aperture area of 57.4 cm(2) with a two-bus bar metallization pattern. This result demonstrates the potential of screen-printing metal contacts to enable the realization of large area PK/c-Si tandem devices