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n-i-p Type perovskite solar cell generally requires air oxidation of Spiro-OMeTAD layer to achieve high power conversion efficiency (PCE). However, the detailed oxidation mechanism is still not fully understood. In...

The wide‐bandgap perovskite solar cell is a crucial part of perovskite/silicon tandem solar cells, which offer an avenue for surpassing the power conversion efficiency (PCE) limit of single‐junction silicon solar cells. However, the actual efficiency of such tandem solar cells today is diminished by the nonradiative recombination losses in the wide‐bandgap perovskite subcells. Here, this work reports a grain regrowth and bifacial passivation (GRBP) strategy to reduce recombination losses at the grain boundaries and perovskite/charge transport layer interfaces simultaneously. This is achieved by a posttreatment of perovskite films with a mixture of methylammonium thiocyanate (MASCN) and phenethylammonium iodide (PEAI). The MASCN induces the regrowth of perovskite grains and simultaneously facilitates the penetration of PEAI into the hole‐transport‐layer (HTL)/perovskite bottom interface. Thereby, the bulk and interface nonradiative recombination losses are reduced and the open‐circuit voltage in solar cells is considerably increased. PCEs of 21.9% and 19.9% for the 1.65‐eV bandgap opaque and semitransparent perovskite solar cells, respectively, are obtained. The encapsulated semitransparent perovskite solar cells retain their initial efficiency following 500 h of operation under one‐sun illumination in ambient conditions. The perovskite/silicon 4‐terminal (4‐T) tandem cells are fabricated with impressive PCEs 29.8% and 28.5% for 0.049 cm2 and 1  cm2 devices, respectively.

Perovskite solar cells (PSCs) longevity is nowadays the bottleneck for their full commercial exploitation. Although lot of research is ongoing, the initial decay of the output power – an effect known as “burn‐in” degradation happening in the first 100 h – is still unavoidable, significantly reducing the overall performance (typically of >20%). In this paper, the origin of the “burn‐in” degradation in n‐i‐p type PSCs is demonstrated that is directly related to Li+ ions migration coming from the SnO2 electron transporting layer visualized by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) measurements. To block the ion movement, a thin cross‐linked [6,6]‐phenyl‐C61‐butyric acid methyl ester layer on top of the SnO2 layer is introduced, resulting in Li+ immobilization. This results in the elimination of the “burn‐in” degradation, showing for the first time a zero “burn‐in” loss in the performances while boosting device power conversion efficiency to >22% for triple‐cation‐based PSCs and >24% for formamidinium‐based (FAPbI3) PSCs, proving the general validity of this approach and creating a new framework for the realization of stable PSCs devices.

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The n‐i‐p type perovskite solar cells suffer unpredictable catastrophic failure under operation, which is a barrier for their commercialization. The fluorescence enhancement at Ag electrode edge and performance recovery after cutting the Ag electrode edge off prove that the shunting position is mainly located at the edge of device. Surface morphology and elemental analyses prove the corrosion of the Ag electrode and the diffusion of Ag+ ions on the edge for aged cells. Moreover, much condensed and larger Ag clusters are formed on the MoO3 layer. Such a contrast is also observed while comparing the central and the edge of the Ag/Spiro‐OMeTAD film. Hence, the catastrophic failure mechanism can be concluded as photon‐induced decomposition of the perovskite film and release reactive iodide species, which diffuse and react with the loose Ag clusters on the edge of the cell. The corrosion of the Ag electrode and the migration of Ag+ ions into Spiro‐OMeTAD and perovskite films lead to the forming of conducting filament that shunts the cell. The more condensed Ag cluster on the MoO3 surface as well as the blocking of holes within the Spiro‐OMeTAD/MoO3 interface successfully prevent the oxidation of Ag electrode and suppress the catastrophic failure.

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Although perovskite solar cells have shown high power conversion efficiency, performance stability is still insufficient. Herein, the decay kinetics of the p–i–n type of perovskite cells under light illumination is monitored. It is found that the degradation of the performance is mainly caused by the decrease in short‐circuit current (JSC), which is directly related to the loss of active area. Secondary ion mass spectrometry (SIMS) analysis confirms that both CH3NH3+ and I− migrate toward the metal electrode during aging through the thin PC61BM layer. Atomic force microscope (AFM) and scanning electron microscope (SEM) analyses reveal that some part of the PC61BM layer is too thin to cover the rough surface of the perovskite film fully. Therefore, chemical corrosion of the metal electrode by CH3NH3I leads to the loss of active area and the consequent short circuit current is proposed to be the performance decay mechanism of perovskite solar cells, which is further supported by the stability improvement of the cells by inserting a thin bathocuproine (BCP) buffer layer between the metal electrode and PC61BM, where the CH3NH3I migration is blocked by the BCP layer.