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Over the past five years, there has been a significant increase in both the intensity of research and the performance of crystalline silicon devices which utilize metal compounds to form carrier-selective heterocontacts. Such heterocontacts are less fundamentally limited and have the potential for lower costs compared to the current industry dominating heavily doped, directly metalized contacts. A low temperature (≤230 °C), TiO x /LiF x /Al electron heterocontact is presented here, which achieves mΩcm 2 scale contact resistivities ρ c on lowly doped n-type substrates. As an extreme demonstration of the potential of this heterocontact, it is trialed in a newly developed, high efficiency n-type solar cell architecture as a partial rear contact (PRC). Despite only contacting ≈1% of the rear surface area, an efficiency of greater than 23% is achieved, setting a new benchmark for n-type solar cells featuring undoped PRCs and confirming the unusually low ρ c of the TiO x /LiF x /Al contact. Finally, in contrast to previous versions of the n-type undoped PRC cell, the performance of this cell is maintained after annealing at 350–400 °C, suggesting its compatibility with conventional surface passivation activation and sintering steps.

Nanometer scale interfacial layers between the metal cathode and the n-type semiconductor play a critical role in enhancing the transport of charge carriers in and out of optoelectronic devices. Here, a range of nanoscale alkali and alkaline earth metal carbonates (i.e., potassium, rubidium, caesium, calcium, strontium, and barium) are shown to function effectively as electron heterocontacts to lightly doped n-type crystalline silicon (c-Si), which is particularly challenging to contact with common metals. These carbonate interlayers are shown to enhance the performance of n-type c-Si proof-of-concept solar cells up to a power conversion efficiency of ≈19%. Furthermore, these devices are thermally stable up to 350 °C and both the caesium and barium carbonates pass a standard 1000 h damp heat test, with >95% of their initial performance maintained. The temperature and humidity stable electron heterocontacts based on alkali and alkaline earth metal carbonates show a high potential for industrial feasibility and longevity for deployment in the field.

Over the past three years a new family of high efficiency n-type crystalline silicon cells featuring passivated partial rear contacts (PRC) has emerged. These cells take advantage of the unique contact properties obtained by introducing thin metal compound interlayers, such as TiO x and LiFx, between the metallic electrode and the silicon absorber. This paper explores the concept and potential advantages of the n-type passivated PRC cell. In particular, the recent fabrication of a cell at 23.1%, featuring a less-than 1% TiOx/LiFx /Al passivated PRC, demonstrates the compatibility of this concept with high efficiency designs.

Research results are presented on the physical mechanisms of minority carrier trapping and recombination in multicrystalline silicon material. Testing methods included measured lifetime injection dependence and gettering experiments, which identified causes of impurities, crystallographic defects and volume recombination.

A high Schottky barrier (>0.65 eV) for electrons is typically found on lightly doped n-type crystalline (c-Si) wafers for a variety of contact metals. This behavior is commonly attributed to the Fermi-level pinning effect and has hindered the development of n-type c-Si solar cells, while its p-type counterparts have been commercialized for several decades, typically utilizing aluminium alloys in full-area, and more recently, partial-area rear contact configurations. Here the authors demonstrate a highly conductive and thermally stable electrode composed of a magnesium oxide/aluminium (MgO x/Al) contact, achieving moderately low resistivity Ohmic contacts on lightly doped n-type c-Si. The electrode, functionalized with nanoscale MgO x films, significantly enhances the performance of n-type c-Si solar cells to a power conversion efficiency of 20%, advancing n-type c-Si solar cells with full-area dopant-free rear contacts to a point of competitiveness with the standard p-type architecture. The low thermal budget of the cathode formation, its dopant-free nature, and the simplicity of the device structure enabled by the MgO x/Al contact open up new possibilities in designing and fabricating low-cost optoelectronic devices, including solar cells, thin film transistors, or light emitting diodes. [ABSTRACT FROM AUTHOR]

Among the metals, magnesium has one of the lowest work functions, with a value of 3.7 eV. This makes it very suitable to form an electron-conductive cathode contact for silicon solar cells. We present here the experimental demonstration of an amorphous silicon/magnesium/aluminium (a-Si:H/Mg/Al) passivating contact for silicon solar cells. The conduction properties of a thermally evaporated Mg/Al contact structure on n-type crystalline silicon (c-Si) are investigated, achieving a low resistivity Ohmic contact to moderately doped n-type c-Si (~5×1015 cm-3) of ~0.31Ωcm2 and ~0.22 Ωcm2 for samples with and without an amorphous silicon passivating interlayer, respectively. Application of the passivating cathode to the whole rear surface of n-type front junction c-Si solar cells leads to a power conversion efficiency of 19% in a proof-of-concept device. The low thermal budget of the cathode formation, its dopant-less nature, and the simplicity of the device structure enabled by the Mg/Al contact open up possibilities in designing and fabricating low-cost silicon solar cells. [ABSTRACT FROM AUTHOR]