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The improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSC) relies on the enhanced quality of perovskite layer and the modification of its adjacent interfaces. For this purpose, a multifunctional organic passivation molecule 1‐(4‐Fluorophenyl) biguanide hydrochloride (F‐BHCl) is introduced to the top and bottom interfaces of the perovskite layer. The PCE of PSC after the modification of double interfaces with F‐BHCl is significantly increased from 22.41% (unmodified) to 25.14%, and the storage, thermal, and operation stability is also improved. The comprehensive theoretical and experimental studies verify that due to its versatile functional groups and adaptation, F‐BHCl can significantly improve the quality of perovskite film, fully passivate several kinds of common defects, smoothen the top surfaces of perovskite film, and construct "molecular bridges" with carrier transporters on both the top and bottom surfaces, leading to significantly reduced non‐recombination and carrier transport losses. As a result, a significant increase is achieved in the open circuit voltage and fill factor as well as the whole performance of the device. [ABSTRACT FROM AUTHOR]

Formamidinium lead triiodide (FAPbI3) with an ideal bandgap and good thermal stability has received wide attention and achieved a record efficiency of 26% in n–i–p (regular) perovskite solar cells (PSCs). However, imperfect FAPbI3 formation on the typical hole transport layer (HTL), high interfacial trap‐state density, and unfavorable energy alignment between the HTL and FAPbI3 result in the inferior photovoltaic performance of p–i–n (inverted) PSCs with FAPbI3 absorber. Herein, the α‐phase FAPbI3 is stabilized by constructing a buffer interface region between the NiOx HTL and FAPbI3, which not only diminishes NiOx/FAPbI3 interfacial reactions and defects but also facilitates carrier transport. Upon the construction of a buffer interface region, FAPbI3 inverted PSC exhibits a high‐power conversion efficiency of 23.56% (certified 22.58%) and excellent stability, retaining 90.7% of its initial efficiency after heating at 80 °C for 1000 h and 84.6% of the initial efficiency after operating at the maximum power point under continuous illumination for 1100 h. Besides, as a light‐emitting diode device, the FAPbI3 inverted PSC can be directly lit with an external quantum efficiency of 1.36%. This study provides a unique and efficient strategy to advance the application of α‐phase FAPbI3 in inverted PSCs. [ABSTRACT FROM AUTHOR]

Optimizing the interface between the perovskite and transport layers is an efficient approach to promote the photovoltaic performance of inverted perovskite solar cells (IPSCs). Given decades of advances in bulk materials optimization, the performance of IPSCs has been pushed to its limits by interface engineering with a power conversion efficiency (PCE) over 25% and excellent stability. Herein, an n‐type polymeric semiconducting material, PY‐IT, that has shown remarkable performance in organic photovoltaics, is introduced as an interface regulator between perovskite and ETL. Encouragingly, this polymerized small molecular acceptor (PSMA) exhibits significant effectiveness in both passivation defects and electron transfer facilitation properties with the merits of strong planarity and rotatable linkers, which significantly optimizes perovskite grain growth orientation and added charge transport channels. As a result, the PSMA‐treated IPSC devices obtain an optimal efficiency of 23.57% with a fill factor of 84%, among the highest efficiency among PSMA‐based IPSCs. Meanwhile, the photo‐stability of PSMA devices is eye‐catching, maintaining ≈80% of its initial PCE after 1000 h of simulated 1‐sun illumination under maximal power point tracking. This work combines the achievements of polymer science and IPSC device engineering to provide a new insight into interface regulation of efficient and stable devices. [ABSTRACT FROM AUTHOR]

There have been huge achievements of all‐perovskite tandem solar cells, which recently realized the highest power conversion efficiency of 24.8%. However, the complex device structure and complicated manufacture processes severely restrict the further development of all‐perovskite tandem solar cells. In this work, we successfully fabricated high‐efficiency hole transport material‐free (HTM‐free) Sn−Pb alloyed narrow bandgap perovskite solar cells (PSCs) by introducing guanidinium thiocyanate (GASCN) and hydroiodic acid (HI) into the perovskite precursor solution. GASCN and HI play a positive synergy effect during perovskite crystallization process resulting in larger grain size, fewer surface defects, and lower trap density to suppress the Sn2+ oxidation degradation. Furthermore, they could effectively adjust the energy level of perovskite materials, reduce the energy level difference between perovskite and ITO resulting in more efficiently transport of free hole charge carriers. As a result, with adding GASCN and HI, the achieved highest power conversion efficiency of HTM‐free devices increased from 12.58% to 17.85%, which is one of the highest PCEs among all values reported to date for the HTM‐free narrow‐bandgap (1.2–1.4 eV) Sn−Pb binary PSCs. Moreover, the optimized device shows improved environmental stability. Our additive strategy manifests a remarkable step towards the facile, cost‐efficient fabrication of HTM‐free perovskite‐based tandem solar cells with both high efficiency and simple fabrication process. [ABSTRACT FROM AUTHOR]

There have been a number of remarkable signs of progress achieved in tin–lead mixed narrow‐bandgap perovskite solar cells (PSCs) due to the high theoretical power conversion efficiency (PCE) and their promising application in tandem devices. Indeed, Sn–Pb mixed PSCs without a hole transport layer (HTL) also have been more attractive owing to lower cost and simplification of the device structure. However, the defects in perovskite film introduced by Sn2+ oxidation severely restrict device efficiency and stability.Herein, a small organic molecule, 4,4'‐sulfonyldiphenol, is employed to passivate perovskite (Eg = 1.26 eV) surface to decrease the interfacial defects and suppress the nonradiative carrier recombination. Furthermore, by regulating energy‐level alignment, charge carrier extraction is greatly facilitated. The device performance is significantly enhanced in that the champion PCE is enlarged to 21.43% with an open‐circuit voltage (Voc) of 0.876 V from only 18.02% with a Voc of 0.770 V. The stability of unencapsulated devices is improved substantially as well while retaining 80% PCE of its initial value after being stored in the glovebox for around 600 h. This facile but highly effective strategy successfully proposes the promising development of HTL‐free Sn–Pb mixed PSCs. [ABSTRACT FROM AUTHOR]

High crystallization and conductivity are always required for inorganic carrier transport materials for cheap and high‐performance inverted perovskite solar cells (PSCs). High temperature and external doping are inevitably introduced and thus greatly hamper the applications of inorganic materials for mass production of flexible and tandem devices. Here, an amorphous and dopant‐free inorganic material, Ni3+‐rich NiOx, is reported to be fabricated by a novel UV irradiation strategy, which is facile, easily scaled‐up, and energy‐saving because all the processing temperatures are below 82 ℃. The as‐prepared NiOx film shows highly improved conductivity and hole extraction ability. The rigid and flexible PSCs present the champion efficiencies of 22.45% and 19.7%, respectively. This work fills the gap of preparing metal oxide films at the temperature below 150 °C for inverted PSCs with the high efficiency of >22%. More importantly, this work upgrades the substantial understanding about inorganic materials to function well as efficient carrier transport layers without external doping and high crystallization. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are considered one of the most promising next‐generation examples of high‐tech photovoltaic energy converters, as they possess an unprecedented power conversion efficiency with low cost. A typical high‐performance PSC generally contains a perovskite active layer sandwiched between an electron‐transport layer (ETL) and a hole‐transport layer (HTL). The ETL and HTL contribute to the charge extraction in the PSC. However, these additional two layers complicate the manufacturing process and raise the cost. To extend this technology for commercialization, it is highly desired that the structure of PSCs is further simplified without sacrificing their photovoltaic performances. Thus, ETL‐free or/and HTL‐free PSCs are developed and attract more and more interest. Herein, the commonly used methods in reducing the defect density and optimizing the energy levels in conventional PSCs in order to simplify their structures are summarized. Then, the development of diverse ETL‐free or/and HTL‐free PSCs is discussed, with the PSCs classified, including their working principles, implemented technologies, remaining challenges, and future perspectives. The aim is to redirect the way toward low‐cost and high‐performance PSCs with the simplest possible architecture. [ABSTRACT FROM AUTHOR]

Perovskite photodetectors are fabricated via structuring a perovskite/organic heterojunction with CH3NH3PbI3 and a high-mobility and stable organic semiconductor dioctylbenzothieno [2,3-b] benzothiophene (C8BTBT), which possess broad range photoresponse from ultraviolet to near-infrared, fast response, and excellent stability. The CH3NH3PbI3/C8BTBT heterojunction photodetectors exhibit an excellent ratio of photocurrent to dark current, Ilight/ Idark, as high as 2.4 × 104, a high responsivity up to 24.8 AW−1, and a fast response of about 4.0 ms. Meanwhile, the photodetectors can maintain 90% performance even exposed in ambient condition without encapsulation for 20 d. In addition, the detailed mechanism is disclosed based on ultraviolet photoemission spectroscopy, steady-state photoluminescence (PL) spectra, and PL lifetime experiments. The C8BTBT layer acts as an efficient hole-extraction layer to let the holes quickly transport to the electrodes due to its perfect filling in the gaps between perovskite grains, as well as its intrinsic high mobility and the energy-level match with the CH3NH3PbI3. The stable C8BTBT layer can well play as a waterproof layer as well to prevent the perovskite CH3NH3PbI3 from the degradation. The research provides an excellent method for fabricating high-performance and stable perovskite photodetectors using perovskite/organic heterojunction. [ABSTRACT FROM AUTHOR]

The stability and degradation process of low-temperature, solution-processed planar heterojunction perovskite solar cells (PHJ-PSCs) with a structure of ITO/PEDOT:PSS/CH 3 NH 3 PbI 3 /PCBM/Al were studied in both nitrogen-filled glovebox and ambient environment (humidity ∼45%). The results suggested that PHJ-PSCs stored in glovebox without encapsulation showed good stability, and the power conversion efficiency ( PCE ) could be kept over 70% of original value even after 30 days. As compared, PHJ-PSCs stored in ambient environment without encapsulation showed an obvious degradation, and the PCE was about 35% of original value just after 1 h exposure in air. However, PHJ-PSCs fabricated with CH 3 NH 3 PbI 3 thin films stored in ambient environment for the different times didn’t show obvious degradation and have the similar performance parameters, suggesting that the degradation of PHJ-PSCs mainly resulted from the interface issues rather than the attenuation of perovskite thin film itself. Furthermore, electrochemical impedance spectroscopy (EIS) characterization indicated that the degradation of photovoltaic performance parameters was prevailingly attributed to the interface degradation. The research provides good understanding to the stability and degradation process of low-temperature, solution-processed PHJ-PSCs, which would facilitate the stability improvement of PHJ-PSCs. [ABSTRACT FROM AUTHOR]

Interface is one of the most important factors to influence the device stability, which directly determines the commercialization of perovskite solar cells (PSCs). The research disclosed the degradation process and mechanism of planar heterojunction (PHJ) PSCs with a structure of ITO/PEDOT:PSS/CH 3 NH 3 PbI 3 /PCBM/Al using in-situ experiments. The degradation of PHJ-PSCs is mainly attributed to the interface decay of perovskite/cathode. Large amount of bubbles formed quickly at the interface and grew up as PHJ-PSCs exposed to air. The cathode electrode easily peeled off from the devices that led to lose the efficiency completely after only 1 h exposure to air. On the other hand, the degradation driven by intrinsic decomposition of perovskite itself under atmosphere (humidity ∼ 45 RH%) was not obvious and the power conversion efficiency ( PCE ) could retain almost the same when only the perovskite layer was exposed to air for 200 h. Furthermore, annealing-free TiO 2 nanocrystalline particles (TiO 2 NPs) as an interface modification layer was inserted into PHJ-PSCs and dramatically improved the stability, of which the PCEs retained over 75% of its initial values after exposure to air for 200 h. The results provide important information to understand the degradation of PSCs and the improvement of the stability, which may potentially accelerate the development and commercialization of PSCs. [ABSTRACT FROM AUTHOR]