Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.

The performance of perovskite solar cells (PSCs) is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pin-type PSCs with undoped organic charge transporting layers. We find significant quasi-Fermi level splitting losses (135 meV) in the perovskite bulk, while interfacial recombination results in an additional free energy loss of 80 meV at each individual interface which limits the open-circuit voltage ( OC ) of the complete cell to ~1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers allows substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm 2 PSCs surpassing 20% efficiency (19.83% certified) with stabilized power output, a high OC (1.17 V) and record fill factor (> 81%).

We quantify recombination losses in the bulk and interfaces for different perovskite compositions and popular charge transport layers.

We introduce new hole-selective contacts for next-generation perovskite photovoltaics and point to design paths for molecular engineering of perfect interfaces.

We demonstrate open-circuit voltages exceeding 1.26 V for CH3NH3PbI3 solar cells by careful process optimization of the perovskite and its interfaces to the electron and hole transport layers. This open-circuit voltage is the highest reported so far in a full MAPI cell stack and only 64 mV below the maximum open circuit voltage that is possible for this material. We confirm these values for the open circuit voltage by independent measurements of the external photoluminescence quantum efficiency reaching values of 5 % for the fully processed solar cell. We further find exceptionally long photoluminescence lifetimes in full cells and in layer stacks involving one or two contact layers. Numerical simulations reveal that these long photoluminescence lifetimes are only possible with extremely low interface recombination velocities between absorber and contact materials.

Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non‐radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.

An approach is proposed to predict the impact of point defects on solar cell performance.

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to prepare the highest efficiency and most stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using a series of alkaline earth metals. We find that low doping levels enable the incorporation of the dopant within the perovskite lattice, whereas high doping concentrations induce surface segregation. The threshold from low to high doping regime correlates to the size of the doping element. We show that the low doping regime results in a more n-type material, while the high doping regime induces a less n-type doping character. Our work provides a comprehensive picture of the unique doping mechanism of halide perovskites, which differs from classical semiconductors. We proved the effectiveness of the low doping regime for the first time, demonstrating highly efficient methylammonium lead iodide based solar cells in both n-i-p and p-i-n architectures.