Ligang Yuan

A thin layer of C₆₀ pyrrolidine tris‐acid is found essential for achieving high efficiency with planar solar cells of Sn‐based perovskites. As a result, a power conversion efficiency of 7.40% is achieved for FASnI₃ solar cells with a planar n–i–p architecture. For the first time, highly efficient Sn‐based hybrid perovskite solar cells on n–i–p architecture is achieved.

Abstract

For solar cell applications, Sn‐based hybrid perovskites have drawn particular interest due to their environmental friendliness. Here, a thin layer of C₆₀ pyrrolidine tris‐acid (CPTA) is found essential for achieving high efficiency with planar solar cells of Sn‐based perovskites. As a result, a power conversion efficiency of 7.40% is achieved for {en}FASnI₃ solar cells with a planar n–i–p architecture, and the device exhibits excellent stability in air. For the first time, highly efficient Sn‐based hybrid perovskite solar cells on n–i–p architecture are achieved. A V _oc of 0.72 V is highlighted as the highest V _oc ever reported for FASnI₃ solar cells.

A comprehensive analytical model capable of quantifying bimolecular, bulk and surface trap‐assisted contributions to the overall nongeminate recombination losses in organic solar cells is reported. Common techniques such as light intensity‐dependent current density–voltage characteristics, capacitance spectroscopy, and open‐circuit voltage decay yield the necessary experimental data to successfully apply this analytical model.

Abstract

In this study, a comprehensive analytical model to quantify the total nongeminate recombination losses, originating from bimolecular as well as bulk and surface trap‐assisted recombination mechanisms in nonfullerene‐based bulk heterojunction organic solar cells is developed. This proposed model is successfully employed to obtain the different contributions to the recombination current of the investigated solar cells under different illumination intensities. Additionally, the model quantitatively describes the experimentally measured open‐circuit voltage versus light intensity dependence. Most importantly, it is possible to calculate the experimental results with the same fitting parameter values from the presented model. The validity of this model is also proven by a combination of other independent, steady‐state, and transient experimental techniques. This new powerful analytical tool will enable researchers in the photovoltaic community to take into account the synergetic contribution from all relevant types of nongeminate recombination losses in different optoelectronic systems and target their analysis of recombination dynamics at any operating voltage.

Spiro‐OMeTAD(TFSI)₂ is successfully employed in the fabrication of highly efficient n–i–p perovskite solar cells as a p‐dopant in the absence of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. With this approach, the proportion of [spiro‐OMeTAD]⁺ is precisely controlled, and the spiro‐OMeTAD(TFSI)₂‐doped devices show a remarkably improved long‐term stability and well‐retained hole‐transporting material (HTM) morphology after aging for 300 h.

Abstract

To date, the most efficient perovskite solar cells (PSCs) employ an n–i–p device architecture that uses a 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) hole‐transporting material (HTM), which achieves optimum conductivity with the addition of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. However, this additive along with its oxidation process leads to poor reproducibility and is detrimental to stability. Herein, a dicationic salt spiro‐OMeTAD(TFSI)₂, is employed as an effective p‐dopant to achieve power conversion efficiencies of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm²) with excellent reproducibility in the absence of LiTFSI and air exposure. As far as it is known, these are the highest‐performing n–i–p PSCs without LiTFSI or air exposure. Comprehensive analysis demonstrates that precise control of the proportion of [spiro‐OMeTAD]⁺ directly provides high conductivity in HTM films with low series resistance, fast hole extraction, and lower interfacial charge recombination. Moreover, the spiro‐OMeTAD(TFSI)₂‐doped devices show improved stability, benefitting from well‐retained HTM morphology without forming aggregates or voids when tested under an ambient atmosphere. A facile approach is presented to fabricate highly efficient PSCs by replacing LiTFSI with spiro‐OMeTAD(TFSI)₂. Furthermore, this study provides an insight into the relationship between device performance and the HTM doping level.

Steric hindrance of side chains is purposely introduced in the design of planar nonfullerene acceptors. Compared with IDTT2F bearing bare thiophene bridge unit, IDTCN‐C, IDTCN‐O, and IDTCN‐S with alkyl, alkoxyl, and alkylthio substituted thiophene bridge units, all display favorable face‐on orientation and strong crystallinity. An excellent power conversion efficiency of 13.28% based on PBDB‐T:IDTCN‐O is achieved without any additives or annealing treatments.

Abstract

A series of alkyl, alkoxyl, and alkylthio substituted A–π–D–π–A type nonfullerene acceptors (NFAs) IDTCN‐C, IDTCN‐O, and IDTCN‐S are designed and synthesized. The introduction of a lateral side chain at the outer position of the π bridge unit can endow the terminal moiety with a confined planar conformation due to the steric hindrance. Thus, compared with nonsubstituted NFA (IDTT2F), these acceptors tend to form favorable face‐on orientation and exhibit strong crystallinity as verified with grazing‐incidence wide‐angle X‐ray scattering measurement. Moreover, the variation of side chain can significantly change the lowest unoccupied molecular orbital (LUMO) energy level of acceptors. As state‐of‐the‐art NFAs, a power conversion efficiency of 13.28% (V _oc = 0.91 V, J _sc = 19.96 mA cm⁻², and FF = 73.2%) is obtained for the as‐cast devices based on IDTCN‐O, which is among the highest value reported in literature. The excellent photovoltaic performance for IDTCN‐O can be attributed to its slightly up‐shifted LUMO level and more balanced charge transport. This research demonstrates side chain engineering is an effective way to achieve high efficiency organic solar cells.

Smart photovoltaic windows with distinguished electrical power generation, energy saving, and privacy protection are enabled by coupling of multiresponsive liquid crystal/polymer composite (LCPC) films and semi‐transparent perovskite solar cells (ST‐PSC). In this design, fast and stable multiresponsive LCPC films are utilized as an inside layer to control the transparency, and high‐performance ST‐PSCs as an outside layer to offer energy generation functionality.

Abstract

Smart photovoltaic windows (SPWs) are functional devices possessing the capabilities of electrical power output, energy saving, and privacy protection by managing sunlight under external stimuli and potentially applicable in the fields of energy‐saving buildings, automobiles, and switchable optoelectronics. However, long response time, low power conversion efficiency (PCE), poor stability and cycling performance, and monostimuli responsive behavior restrict their practical applications. To address these issues, high‐efficiency and reliable SPWs are demonstrated by coupling multiresponsive liquid crystal/polymer composite (LCPC) films and semi‐transparent perovskite solar cells (ST‐PSCs). In this design, fast and multiple stimuli‐responsive LCPC films are utilized as an inside layer to control the transparency of SPWs. The ST‐PSCs with competitive PCE and qualified transparency acting as an outside layer offer energy generation functionality. Benefiting from repeatable transparency transition modulated by external stimuli, a series of working modes are achieved in the SPWs providing distinguished and stable energy generation, energy saving, and privacy protection performances.

A powerful flexible transparent electrode based on nanopatterned silver nanowires is realized to efficiently release trapped light in flexible organic light‐emitting diodes, leading to a maximum external quantum efficiency of 61.7% and power efficiency of 126.6 lm W⁻¹ for white emission.

Abstract

Flexible organic light‐emitting diodes (OLEDs) are attracting tremendous attention due to their promise as a key element in bendable display and curved lighting applications. However, their performance in terms of efficiency and bendability is limited, since flexible transparent electrodes with superior electrical, optical, and mechanical properties are rare. Here, a multifunctional electrode architecture that is based on flexible plastic, and consists of electrically conductive silver nanowires, a nanopatterned ZnO outcoupling layer, and a hole‐injection polymer layer, is proposed for the actualization of high‐performance flexible OLEDs. The trapped light in the waveguide and substrate modes is effectively released by integrating aperiodic nanostructures into high‐refractive‐index ZnO layers on both sides of the plastic substrate. A maximum external quantum efficiency of 61.7% and a power efficiency of 126.6 lm W⁻¹ are achieved for the white‐emission flexible OLEDs with broadband and angle‐independent outcoupling enhancement. In addition, the proposed approach allows for high‐level mechanical flexibility, retaining over 80% of the initial efficiency after 3000 cycles of repeated bending.

TETAPb₂Br₈, a 1D ladder‐like organic–inorganic hybrid compound, emits white light due to radiative recombinations of self‐trapped excitons (STEs). In the low‐temperature range, the photoluminescence intensity as well as the STE lifetime increase with increasing temperature. This negative thermal quenching of emission is due to transitions between polaronic states involving exciton–phonon interaction.

Abstract

The synthesis and the optical properties of a new organic–inorganic hybrid material (C₆H₂₂N₄)[Pb₂Br₈] (abbreviated as TETAPb₂Br₈) is reported here. Its ladder‐like crystal structure is built up from infinite 1D chains of corner‐sharing [Pb₂Br₈]⁴⁻ bi‐octahedra surrounded by tetra‐protonated triethylenetetramine (abbreviated as TETA⁴⁺) organic cations. Under UV excitation, this hybrid organic–inorganic compound emits white light due to radiative recombinations of self‐trapped excitons associated with a structural distortion of the PbBr₆ octahedra. Thin films of TETAPb₂Br₈ show a photoluminescence (PL) quantum yield of ≈11% and exhibit a Commission Internationale de l'Eclairage coordinates of (0.32, 0.37). In the low‐temperature range, the PL intensity increases with increasing temperature. This negative thermal quenching of white‐light emission is interpreted in terms of transitions between excitonic states involving an exciton–phonon interaction. The interpretations are supported by the temperature dependence of the resonant Raman scattering and by density functional theory calculations.

A high power conversion efficiency of 13.5% achieved with single‐junction ternary polymer solar cells based on PTB7‐Th, PC₇₁BM, and COi8DFIC is fabricated by slot‐die coating. This work extends to the fabrication of large‐area modules, and also to roll‐to‐roll fabrication, and demonstrates the strong potential of the slot‐die coated ternary system for commercial applications.

Abstract

The record efficiency of the state‐of‐the‐art polymer solar cells (PSCs) is rapidly increasing, due to the discovery of high‐performance photoactive donor and acceptor materials. However, strong questions remain as to whether such high‐efficiency PSCs can be produced by scalable processes. This paper reports a high power conversion efficiency (PCE) of 13.5% achieved with single‐junction ternary PSCs based on PTB7‐Th, PC₇₁BM, and COi8DFIC fabricated by slot‐die coating, which shows the highest PCE ever reported in PSCs fabricated by a scalable process. To understand the origin of the high performance of the slot‐die coated device, slot‐die coated photoactive films and devices are systematically investigated. These results indicate that the good performance of the slot‐die PSCs can be due to a favorable molecule‐structure and film‐morphology change by introducing 1,8‐diiodooctane and heat treatment, which can lead to improved charge transport with reduced carrier recombination. The optimized condition is then used for the fabrication of large‐area modules and also for roll‐to‐roll fabrication. The slot‐die coated module with 30 cm² active‐area and roll‐to‐roll produced flexible PSC has shown 8.6% and 9.6%, respectively. These efficiencies are the highest in each category and demonstrate the strong potential of the slot‐die coated ternary system for commercial applications.

Temperature‐dependent X‐ray diffraction, absorption and photoluminescence measurements on methylammonium lead iodide thin films with grain sizes ranging from the micrometer to the tens of nanometer scale reveal that the low‐temperature phase transition is increasingly suppressed with decreasing grain size. These results unveil the remarkable sensitivity of optoelectronic and structural properties to the local environment in perovskite thin films.

Abstract

Grain size in polycrystalline halide perovskite films is known to have an impact on the optoelectronic properties of the films, but its influence on their soft structural properties and phase transitions is unclear. Here, temperature‐dependent X‐ray diffraction, absorption, and macro‐ and micro‐photoluminescence measurements are used to investigate the tetragonal to orthorhombic phase transition in thin methylammonium lead iodide films with grain sizes ranging from the micrometer scale down to the tens of nanometer scale. It is shown that the phase transition nominally at ≈150 K is increasingly suppressed with decreasing grain size and, in the smallest grains, the first evidence of a phase transition is only seen at temperatures as low as ≈80 K. With decreasing grain size, an increasing magnitude of the hysteresis is also seen in the structural and optoelectronic properties when cooling to, and then upon heating from, 100 K. This work reveals the remarkable sensitivity of the optoelectronic, physical, and phase properties to the local environment of the perovskite structure, which will have large ramifications for phase and defect engineering in operating devices.

Sn‐based perovskite solar cells (PSCs) with 6.33% power conversion efficiency are fabricated with an aperture area of 1 cm² by introducing a post‐deposition vapor annealing method. The fabricated Sn‐based PSCs show promising stability, both under dark and maximum power‐point tracking conditions.

Sn‐based perovskite solar cells (PSCs) are promising alternatives to replacing toxic Pb‐based PSCs, which have shown a rapid rise in photovoltaic applications in the past 1 year. However, the reported Sn‐based PSCs are often fabricated with a small aperture area (typically 0.02–0.1 cm²) because forming homogeneous pinhole‐free continuous films over a large surface area is still challenging. Herein, a post‐deposition vapor annealing (PDVA) process assisted by methylammonium chloride vapor is presented that enables the fabrication of stable, homogeneous pinhole‐free FASnI₃ perovskite absorber films with low crystal defects and low surface recombination over a relatively large area up to 1.02 cm². Inverted planar solar cells fabricated with a 1.02 cm² aperture area show a maximum power conversion efficiency of 6.33% with high reproducibility and stability. The shelf‐lifetime stability test shows that the PSCs retain 90% of their performance for more than 1000 h when stored in a N₂‐filled glove box and under dark conditions. The preliminary light‐soaking stability tests under continuous illumination and maximum power‐tracking conditions are relatively promising. This study marks an important step toward the up scaling of Sn‐based PSCs.

High‐performance perovskite solar cells with an average power conversion efficiency of 21.4% are achieved based on mixed 2D/3D perovskites with induced phenylethylammonium iodide and exhibit an ultrahigh fill factor (83.6%). The unencapsulated device exhibits enhanced operational stability under continuous simulated sunlight illumination and outstanding air stability after 1000 h of storage under ambient air conditions.

2D/3D perovskite heterostructures or composites are recognized as efficient strategies to improve the stability of perovskite solar cells. Herein, a novel solution process to develop 2D/3D perovskites with modulated diffusion passivation by introducing phenylethylammonium iodide (PEAI) and N,N‐dimethylformamide (DMF) additive, which could effectively enhance device performance and long‐term stability, is demonstrated. Compared with conventional devices, the device with PEAI and DMF solvent additive treatment exhibit enhanced charge transport, improved charge extraction, and suppressed nonradiative carrier recombination. The solar cells with an optimal 2D/3D perovskite passivation treatment exhibit an extremely high fill factor of 83.6% and an average power conversion efficiency of 21.4% (21.3% using integrated photocurrent from the incident photon‐to‐current efficiency spectra) based on the NiO _x hole transport layer. Furthermore, the unencapsulated device exhibits excellent stability under continuously simulated sunlight illumination and outstanding air stability after 1000 h of storage under ambient air conditions.

Fullerene‐free ternary polymer solar cells with small energy loss and broad energy levels offsets are reported by employing a blend of two fullerene‐free small molecules as electron acceptors. A power conversion efficiency of 11.22% is achieved with an open‐circuit voltage of 0.78V, a short‐circuit current density of 20.71 mA cm^‐2 and a fill factor of 0.695.

Abstract

Ternary polymer solar cells (PSCs) are fabricated that consisted of a blend of IEICO‐4F and 3TT‐FIC as electron acceptors and PBDB‐T as an electron donor. The power conversion efficiency (PCE) of ternary PSCs is increased from 9.9% to 11.22% via the blend of IEICO‐4F and 3TT‐FIC as electron acceptors (the ratio of IEICO‐4F:3TT‐FIC is 6:4), which enhances the open‐circuit voltage (V _OC) from 0.71 to 0.78 V. The main contribution of the blended acceptor is its broad energy level offset between the donor and acceptor (from 1.26 to 1.30 eV) due to the enhanced lowest unoccupied molecular orbital energy levels of the blended acceptor. Meanwhile, the small energy losses of the ternary photoactive layer (reduced from 0.55 to 0.52 eV) are simultaneously due to the more efficient exciton dissociation and the suppressed charge carrier recombination. This work provides an effective strategy for improving the photovoltaic performance of binary PSCs.

Eco‐compatible solvent‐processed organic photovoltaic cells with over 16% power conversion efficiency are achieved via modifying the flexible alkyl chains of BTP‐4F‐8. Combining with the polymer donor T1, over 14% power conversion efficiencies are obtained not only for using several kinds of greener solvents like o‐xylene, 1,2,4‐trimethylbenzene, and tetrahydrofuran but also for 1.07 cm² cells by the blade‐coating method.

Abstract

Recent advances in nonfullerene acceptors (NFAs) have enabled the rapid increase in power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. However, this progress is achieved using highly toxic solvents, which are not suitable for the scalable large‐area processing method, becoming one of the biggest factors hindering the mass production and commercial applications of OPVs. Therefore, it is of great importance to get good eco‐compatible processability when designing efficient OPV materials. Here, to achieve high efficiency and good processability of the NFAs in eco‐compatible solvents, the flexible alkyl chains of the highly efficient NFA BTP‐4F‐8 (also known as Y6) are modified and BTP‐4F‐12 is synthesized. Combining with the polymer donor PBDB‐TF, BTP‐4F‐12 shows the best PCE of 16.4%. Importantly, when the polymer donor PBDB‐TF is replaced by T1 with better solubility, various eco‐compatible solvents can be applied to fabricate OPV cells. Finally, over 14% efficiency is obtained with tetrahydrofuran (THF) as the processing solvent for 1.07 cm² OPV cells by the blade‐coating method. These results indicate that the simple modification of the side chain can be used to tune the processability of active layer materials and thus make it more applicable for the mass production with environmentally benign solvents.

Nickel oxide (NiO _x )‐based carrier‐selective contact Ag/ITO/NiO _x /n‐Si/LiF _x /Al solar cells are fabricated. The highest reported power conversion efficiency of ≈15.20% is achieved with a chemically grown SiO _x passivation layer on silicon in comparison with devices without SiO _x (efficiency ≈12.43%). Devices are analyzed systematically for performance enhancement with SiO _x and evidence for contact‐resistivity, minority‐carriers' lifetimes/diffusion‐lengths, recombination‐resistance, and density of interface‐defect‐states at the NiO _x /n‐Si interface is provided.

Carrier‐selective contact‐based silicon heterojunction solar cells are fabricated using nickel oxide (NiO _x ) as a hole‐selective layer by thermal evaporation. The highest power conversion efficiency of ≈15.20% with a chemically grown SiO _x interlayer is achieved from a Ag/ITO/NiO _x /n‐Si/LiF _x /Al cell structure in comparison with ≈12.43% without SiO _x . The cells without and with the SiO _x layer are analyzed by considering crucial parameters for conversion efficiency, such as minority carriers' diffusion lengths, lifetimes, recombination resistance, and density of interface defect states at the NiO _x /n‐Si junction, by studying the dark/light current density–voltage, quantum efficiency, impedance, and parallel conductance characteristics. Device analysis provides evidence for the cell's open‐circuit voltage and short‐circuit current enhancement with the SiO _x interlayer. This is due to an improvement in minority carrier lifetimes from ≈8.6 to ≈48.27 μs (photo‐conductance decay analysis), which is also estimated from ≈7.45 to ≈49.20 μs by impedance spectra analysis, increased minority carrier diffusion length from ≈171 to ≈952 μm, and decreased rear surface recombination velocity from ≈1106 to ≈170 cm s⁻¹ (quantum efficiency analysis). These investigations reveal that engineering the n‐Si/LiF _x interface by the SiO _x interlayer is more important than the NiO _x /n‐Si interface because of a thin unintentionally grown SiO _x layer during NiO _x evaporation simultaneously mediating silicon surface passivation.

With the synthesis of two novel hole transport materials, the inverted planar perovskite solar cell achieves a high fill factor of 81.7%, with an efficiency exceeding 19%. More importantly, a highly possible correlation between the molecular packing, hole mobility, and device performance is revealed, which provides some insights for the rational design of hole transport materials.

Abstract

In this paper, two novel D‐π‐D hole‐transporting materials (HTM) are reported, abbreviated as BDT‐PTZ and BDT‐POZ, which consist of 4,8‐di(hexylthio)‐benzo[1,2‐b:4,5‐b′]dithiophene (BDT) as π‐conjugated linker, and N‐(6‐bromohexyl) phenothiazine (PTZ)/N‐(6‐bromohexyl) phenoxazine (POZ) as donor units. The above two HTMs are deployed in p‐i‐n perovskite solar cells (PSCs) as dopant‐free HT layers, exhibiting excellent power conversion efficiencies of 18.26% and 19.16%, respectively. Particularly, BDT‐POZ demonstrates a superior fill factor of 81.7%, which is consistent with its more efficient hole extraction and transport verified via steady‐state/transient fluorescence spectra and space‐charge‐limited current technique. Single‐crystal X‐ray diffraction characterization implies these two molecules present diverse packing tendencies, which may account for various interfacial hole‐transport ability in PSCs.

A temperature‐tuned antisolvent bathing method is introduced for fabricating highly oriented and large‐grain perovskite thin films. Using large‐area compatible cold antisolvent bathing, a high‐quality perovskite film is obtained with a reduced defect density and an enhanced charge‐carrier extraction capability, which achieves a champion power‐conversion efficiency of 18.50%.

Abstract

Scaling large‐area solar cells is in high demand for the commercialization of perovskite solar cells (PSCs) with a high power‐conversion efficiency (PCE). However, few roll‐to‐roll‐compatible deposition methods for the formation of highly oriented uniform perovskite films are reported. Herein, a facile cold antisolvent bathing approach compatible with large‐area fabrication is introduced. The wet precursor films are submerged in a cold antisolvent bath at 0 °C, and the retarded nucleation and growth kinetics allow highly oriented perovskite to be grown along the [110] and [220] directions, perpendicular to the substrate. The high degree of the preferred crystal orientation benefits the effective charge extraction and reduces the amount of inter‐ and intra‐grain defects inside the perovskite films, improving the PCE from 16.48% (ambient‐bathed solar cell) to 18.50% (cold‐bathed counterpart). The cold antisolvent bathing method is employed for the fabrication of large‐area (8 × 10 cm²) PSCs with uniform photovoltaic device parameters, thereby verifying the scale‐up capability of the method.

A new method of depressing E _loss for nonfullerene organic solar cells (OSCs) is reported, in which a small molecular material (NRM‐1) can be selectively dispersed into the acceptor phase in the PBDB‐T:IT‐4F‐based OSC, resulting in lower Elossrad and Elossnonrad and hence significant improvement in V _OC, and under an optimal feed ratio of NRM‐1, an enhanced efficiency can be gained.

Abstract

Reducing energy loss (E _loss) is of critical importance to improving the photovoltaic performance of organic solar cells (OSCs). Although nonradiative recombination (Elossnonrad) is investigated in quite a few works, the method for modulating Elossnonrad is seldom reported. Here, a new method of depressing E _loss is reported for nonfullerene OSCs. In addition to ternary‐blend bulk heterojunction (BHJ) solar cells, it is proved that a small molecular material (NRM‐1) can be selectively dispersed into the acceptor phase in the PBDB‐T:IT‐4F‐based OSC, resulting in lower Elossrad and Elossnonrad, and hence a significant improvement in the open‐circuit voltage (V _OC); under an optimal feed ratio of NRM‐1, an enhanced power conversion efficiency can also be gained. Moreover, the role of NRM‐1 in the method is illustrated and its applicability for several other representative OSCs is validated. This work paves a new pathway to reduce the E _loss for nonfullerene OSCs.

A major drawback of hybrid perovskites is the lack of long‐term stability. This is related to the degradation of organic cations. Light‐induced degradation of CH₃NH₃PbI₃ extends from ambient temperatures down to 5 K. Illumination of thin films and single crystals at T = 5 K causes the formation of localized states that can be annealed at T ≥ 15 K.

In a period of only a few years, the power conversion efficiency of organic–inorganic perovskite solar cells has surpassed a value of 24.2%. However, a major drawback is the lack of long‐term stability, which is partially related to the dissociation of organic cations under prolonged illumination. This degradation mechanism is not limited to ambient temperatures. At low temperatures (T = 5 K), illumination of methyl ammonium lead iodide (CH₃NH₃PbI₃) thin films with a photon energy of E _ph = 3.4 eV results in the formation of localized trap states located about 100 meV within the bandgap. These light‐induced defects are metastable, and annealing at T ≥ 15 K removes the localized states. Defect creation is not limited to polycrystalline perovskites but is also observed in single‐crystal CH₃NH₃PbI₃. The experimental data are discussed in terms of a two‐level model where the metastable state is separated from the annealed state by an energy barrier.