The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in by up to 100 millivolts. We achieved a high of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non‐exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift‐off strategy. By establishing the microstructure–property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub‐microscale extended imperfections and lead‐halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation‐molecule‐assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

such as charge-carrier lifetimes and diffusion lengths in perovskite films should be maximized, which are sensitive to the density of sub-bandgap trap states acting as nonradiative recombination centers. [12,13] Long carrier lifetimes and diffusion lengths imply a reduction in trap densities constituted by multidimensional defects that can be broadly observed at the grain boundaries and surfaces of polycrystalline perovskite films. Therefore, defect modulation to efficiently suppress the undesired nonradiative recombination pathways in perovskite films have resulted in dramatically enhanced carrier lifetimes and diffusion lengths, which can be translated into higher open-circuit voltage (V OC) of photovoltaic devices. [14-18] Recently, surface post-treatments, such as depositing a layer of ammonium salts onto the perovskites, are the most frequently employed strategies, passivating the defects in the topmost area of the perovskite films. [19-22] However, the additional depositing procedure is considered to bring much uncertainty to the original perovskite films. [23,24] Recently, Yoo et al. demonstrated that the commonly used solvents (e.g., isopropanol) for dissolving ammonium salts, due to their strong polarity, had negative effects on the underlying perovskite films. [25] Lead halide perovskite films have witnessed rapid progress in optoelectronic devices, whereas polycrystalline heterogeneities and serious native defects in films are still responsible for undesired recombination pathways, causing insufficient utilization of photon-generated charge carriers. Here, radiationenhanced polycrystalline perovskite films with ultralong carrier lifetimes exceeding 6 μs and single-crystal-like electron-hole diffusion lengths of more than 5 μm are achieved. Prolongation of charge-carrier activities is attributed to the electronic structure regulation and the defect elimination at crystal boundaries in the perovskite with the introduction of phenylmethylammonium iodide. The introduced electron-rich anchor molecules around the host crystals prefer to fill the halide/organic vacancies at the boundaries, rather than form low-dimensional phases or be inserted into the original lattice. The weakening of the electron-phonon coupling and the excitonic features of the photogenerated carriers in the optimized films, which together contribute to the enhancement of carrier separation and transportation, are further confirmed. Finally the resultant perovskite films in fully operating solar cells with champion efficiency of 23.32% are validated and a minimum voltage deficit of 0.39 V is realized. Polycrystalline halide perovskites are of enormous excitement to be applied in highly efficient solar cells, [1-3] light-emitting diodes, [4] lasers, [5,6] and high-sensitivity photodetectors [7,8] due to their low fabricating costs [9,10] and excellent optoelectronic properties. [11] In order for these optoelectronic devices to access their theoretical performance limits, key metrics

The general chemical formula of metal halide perovskite is ABX 3 , where A is a monovalent cation (such as FA + [ formamidinium], MA + [methylammonium], or Cs + ), B is a divalent metal cation (such as Pb 2+ , Sn 2+ , or Ge 2+ ), and X is a monovalent halogen anion (such as I − , Br − , or Cl − ). [9] Photovoltaic devices based on perovskite absorbers have achieved a certified power conversion efficiency (PCE) of 25.5% [10] in single-junction devices and obtained a PCE above 26.7% [11] in tandem devices, in which the best PCE is comparable to those of some commercially available products on the photovoltaic market, such as crystalline silicon (HIT, champion PCE of 26.7%), cadmium telluride (CdTe, champion PCE of 22.1%), gallium arsenide (GaAs, champion PCE of 27.8%), and copper indium gallium selenide (CIGS, champion PCE of 23.4%) solar cells. In particular, only sub-micron-thick absorber is needed in perovskite solar cells because of perovskite's high optical absorption coefficient of about 10 4 cm −1 , [12] therefore high specific power is expected. Combined with the low-temperature solution processability and radiation resistance, [13] these features render PSCs as a Metal halide perovskites have aroused burgeoning interest in the field of photovoltaics owing to their versatile optoelectronic properties. The outstanding power conversion efficiency, high specific power (i.e., power to weight ratio), compatibility with flexible substrates, and excellent radiation resistance of perovskite solar cells (PSCs) enable them to be a promising candidate for next-generation space photovoltaic technology. Nevertheless, compared with other practical space photovoltaics, such as silicon and III-V multi-junction compound solar cells, the research on PSCs for space applications is just in the infancy stage. Therefore, there are considerable interests in further strengthening relevant research from the perspective of both mechanism and technology. Consequently, the approaches used for and the consequences of PSCs for space applications are reviewed. This review provides an overview of recent progress in PSCs for space applications in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments.

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Defects at the bulk grain boundaries and heterojunction interfaces could dictate the power losses of perovskite solar cells (PSCs) during the operation process, which are regarded as major roadblocks towards...

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