Reducing interface recombination boosts the Voc for perovskite solar cells.

Rapid development of both efficiency 1 and stability 2 mean that perovskite solar cells are at the forefront of emerging photovoltaic technologies. State-of-the-art cells exhibit voltage losses 3-8 approaching the theoretical minimum and near-unity internal quantum efficiency 9-13 , but conversion efficiencies are limited by the fill-factor (FF < 83%, below the Shockley-Queisser limit of ~90%). This limitation results from non-ideal charge transport between the perovskite absorber and the cell's electrodes 5,8,13-16 . Reducing the electrical series resistance of charge transport layers is therefore crucial for improving efficiency. Here we introduce a reverse-doping process to fabricate nitrogen-doped titanium oxide electron transport layers with outstanding charge transport performance. By incorporating this charge transport material into perovskite solar cells, we demonstrate 1cm 2 cells with FFs >86%, and an average FF ~ 85.3%. We also report a certified steady-state efficiency record of 22.6% for a 1cm 2 cell (23.33% ± 0.58% from reverse current-voltage scan).Nitrogen-doped titanium oxide (titanium oxynitride, TiO x N y ) has been widely investigated for photocatalysis 17,18 , but rarely in perovskite solar cells (PSCs). PSCs incorporating solution-processed TiO x N y have been reported, but device performances have

The article commences with a review focusing on three critical aspects of the perovskite/Si tandem technology: the evolution of efficiencies to date, comparisons of Si subcell choices, and the interconnection design strategies. Building on this review, a clear route is provided for minimizing optical losses aided by optical simulations of a recently reported high‐efficiency perovskite/Si tandem system, optimizations which result in tandem current densities of ≈20 mAcm−2 with front‐side texture. The primary focus is on electrical modeling on the Si‐subcell, in order to understand the efficiency potential of this cell under filtered light in a tandem configuration. The possibility of increasing the Si subcell efficiency by 1% absolute is offered through joint improvements to the bulk lifetime, which exceeds 4 ms, and improves surface passivation quality to saturation current densities below 10 fA cm−2. Polycrystalline‐Si/SiOx passivating contacts are proposed as a promising alternative to partial‐area rear contacts, with the potential for further simplifying cell fabrication and improving device performance. A combination of optical modeling of the complete tandem structure alongside electrical modeling of the Si‐subcell, both with state‐of‐the‐art modeling tools, provides the first complete picture of the practical efficiency potential of perovskite/Si tandems.

The open‐circuit voltage (VOC) and fill factor are key performance parameters of solar cells, and understanding the underlying mechanisms that limit these parameters in real devices is critical to their optimization. Device modeling is combined with luminescence and cell current–voltage (I–V) measurements to show that carrier transport limitations within the cell can significantly reduce the cell voltage around the maximum power point as well as, under certain conditions, at VOC. An important consequence is that the cell terminal voltage cannot be assumed a priori to be only limited by parasitic recombination. It is demonstrated that luminescence‐based measurements can be used to reconstruct cell I–V curves with removal of any transport limitation effects, which allows the contribution of recombination, shunt resistance, and series resistance on the fill factor to be clarified. Such luminescence‐based measurements allow the contactless characterization of cells and cell precursor structures, and should prove highly valuable as a diagnostic tool for the development of new cell structures and large‐area cells.