to 20.1% [ 2,3 ] within fi ve years. The theoretical limit of the PVSC effi ciency has been estimated to be 31%, which is very close to the Shockley-Queisser limit (33%). [ 4 ] Perovskite deposition is crucial to produce high-effi ciency PVSCs. Generally, there are mainly three methods, including onestep solution spin-coating, vacuum vapor deposition, and two-step sequential deposition to prepare the hybrid perovskite fi lm. [5][6][7][8][9][10][11][12][13] Two-step sequential deposition has recently been reported, [ 7 ] which provides an effi cient and low-cost route to high-performance PVSCs.In a typical two-step sequential deposition of perovskites such as MAPbI 3 (MA = CH 3 NH 3 + ), PbI 2 is fi rst deposited on the substrate (mesoporous or planar scaffold) by spin-coating or vacuum evaporation, subsequently transformed into the perovskite (MAPbI 3 ) by exposing it to an anhydrous isopropanol (IPA) solution of MAI. For the two-step sequential deposition, the conversion and fi lm morphology of the fi nal perovskite fi lm strongly depend on the initial PbI 2 fi lm during the fi rst step of the process. [ 7,14,15 ] Conventionally, PbI 2 from dimethyl formamide (DMF) solution tends to form a layered and dense crystalline fi lm on a fl at substrate. However, the complete conversion of PbI 2 to perovskite on exposure to the MAI solution usually requires several hours. [ 7 ] However, this long reaction time in MAI solution could lead to the dissolution of perovskite fi lms. These drawbacks make it diffi cult to fabricate planar-structured PVSCs by sequential deposition method.Several strategies have been developed to solve this problem, including using elevated reaction temperature, [ 16,17 ] controlling the crystallization of PbI 2 by employing strong coordinative solvent of dimethyl sulfoxide [ 14 ] or using MAI vapor instead of MAI solution. [ 18 ] Recently, a cloudy PbI 2 fi lm prepared by gas-quenching treatment has been reported by Vak and co-workers, [ 19 ] which also enhances the conversion of PbI 2 to perovskites in the process of roll-to-roll fabrication. Zhao & Zhu [ 14 ] developed a new three-step sequential deposition process, where a unstable PbI 2 ·CH 3 NH 3 Cl precursor fi lm is fi rst deposited on the mesoporous TiO 2 substrate and followed by thermal decomposition to form PbI 2 fi lm; the PbI 2 fi lm The photovoltaic performance of perovskite solar cells (PVSCs) is extremely dependent on the morphology and crystallization of the perovskite fi lm, which is affected by the deposition method. In this work, a new approach is demonstrated for forming the PbI 2 nanostructure and the use of high CH 3 NH 3 I concentration which are adopted to form high-quality (smooth and PbI 2 residue-free) perovskite fi lm with better photovoltaic performances. On the one hand, self-assembled porous PbI 2 is formed by incorporating small amount of rationally chosen additives into the PbI 2 precursor solutions, which signifi cantly facilitate the conversion of perovskite without any PbI 2 residue. On the other hand, by...

While methylammonium lead iodide (MAPbI3) with interesting properties, such as a direct band gap, high and well-balanced electron/hole mobilities, as well as long electron/hole diffusion length, is a potential candidate to become the light absorbers in photodetectors, the challenges for realizing efficient perovskite photodetectors are to suppress dark current, to increase linear dynamic range, and to achieve high specific detectivity and fast response speed. Here, we demonstrate NiOx:PbI2 nanocomposite structures, which can offer dual roles of functioning as an efficient hole extraction layer and favoring the formation of high-quality MAPbI3 to address these challenges. We introduce a room-temperature solution process to form the NiOx:PbI2 nanocomposite structures. The nanocomposite structures facilitate the growth of the compact and ordered MAPbI3 crystalline films, which is essential for efficient photodetectors. Furthermore, the nanocomposite structures work as an effective hole extraction layer, which provides a large electron injection barrier and favorable hole extraction as well as passivates the surface of the perovskite, leading to suppressed dark current and enhanced photocurrent. By optimizing the NiOx:PbI2 nanocomposite structures, a low dark current density of 2 × 10(-10) A/cm(2) at -200 mV and a large linear dynamic range of 112 dB are achieved. Meanwhile, a high responsivity in the visible spectral range of 450-750 nm, a large measured specific detectivity approaching 10(13) Jones, and a fast fall time of 168 ns are demonstrated. The high-performance perovskite photodetectors demonstrated here offer a promising candidate for low-cost and high-performance near-ultraviolet-visible photodetection.

While SnPb alloyed perovskites have been considered as an effective approach to broaden the absorption spectrum, it is still challenging to modify the crystallization (and thus morphology, crystallinity, and orientation) in a controllable manner and thus boost the efficiency of SnPb alloyed perovskite solar cells. Here, it is unveiled that controlling the crystallization of CH3NH3Sn0.25Pb0.75I3 films can be simply realized by adjusting the amount of dimethyl sulfoxide in precursors, which has not been reported in SnPb alloyed perovskite systems. The remarkable perovskite crystallinity enhancement by the 20‐fold enhanced (110) plane intensity in the X‐ray diffraction spectrum of CH3NH3Sn0.25Pb0.75I3 and the preferred (110) orientation with the texture coefficient enhanced by 2.6 times to reach 0.88 are demonstrated. Importantly, it is discovered that the introduction of dimethyl sulfoxide avoids the formation of the colloidal coagulation observed in prolonged‐storage precursors and ameliorates inhomogeneous Sn/Pb distributions in resultant perovskite films. Through optimizing perovskite films and device structures, hysteresis‐free planar‐heterojunction CH3NH3Sn0.25Pb0.75I3 solar cells with the efficiency reaching 15.2%, which are the most efficient SnPb alloy‐based perovskite solar cells, are achieved.

Solution‐processed and low‐temperature Sn‐rich perovskites show their low bandgap of about 1.2 eV, enabling potential applications in next‐generation cost‐effective ultraviolet (UV)–visible (vis)–near infrared (NIR) photodetection. Particularly, the crystallization (crystallinity and orientation) and film (smooth and dense film) properties of Sn‐rich perovskites are critical for efficient photodetectors, but are limitedly studied. Here, controllable crystallization for growing high‐quality films with the improvements of increased crystallinity and strengthened preferred orientation through a introducing rubidium cation into the methylammonium Sn‐Pb perovskite system (65% Sn) is achieved. Fundamentally, the theoretical results show that rubidium incorporation causes lower surface energy of (110) plane, facilitating growth in the dominating plane and suppressing growth of other competing planes. Consequently, the methylammonium‐rubidium Sn‐Pb perovskite photodetectors simultaneously achieve larger photocurrent and lower noise current. Finally, highly efficient UV–vis–NIR (300–1100 nm) photodetectors with record‐high linear dynamic range of 110 and 3 dB cut‐off frequency reaching 1 MHz are demonstrated. This work contributes to enriching the cation selection in Sn‐Pb perovskite systems and offering a promising candidate for low‐cost UV–vis–NIR photodetection.

mechanism and quantify the efficiency loss for perovskite solar cells.The analysis and quantification of efficiency loss of solar cells can be done by the drift-diffusion model, [24,25] circuit model, [26,27] and detailed balance model. [28,29] Due to a high nonlinearity of coupled equations and a complex device configuration, drift-diffusion model is difficult to retrieve simulation parameters from the measured current density-voltage (J-V) curves. The parameters include recombination rate, mobility, energy levels (e.g., conduction band, valence band, and work function), effective density of states, and injection/extraction barrier heights. Furthermore, the drift-diffusion model is nontrivial to describe the photon recycling effect correctly. [30] Concerning the circuit model, it requires to retrieve five parameters in modeling. Hence, the uniqueness of the parameters is questionable. Also, the ideality factor in the circuit model has ambiguous physical meaning and cannot quantitatively represent radiative recombination (photon recycling) and nonradiative (Auger and Shockley-Read-Hall) recombination separately. Additionally, while the traditional detailed balance model demonstrates a strong capability to predict the efficiency limit of an ideal solar cell, the model cannot quantify the energy loss of a practical solar cell including optical and electrical (thermodynamic) loss. In this work, a revised detailed balance model is proposed to unveil the loss mechanism and quantify the loss factors of perovskite solar cells. Through investigating the device performance of various fabricated perovskite solar cells, the three dominant loss factors of optical loss, nonradiative recombination loss, and ohmic loss are identified quantitatively. The perovskite-interface-induced surface recombination, ohmic loss, and current leakage are also analyzed. Consequently, the work offers a guideline to the researchers for optimizing perovskite solar cells and ultimately approaching the Shockley-Queisser limit of photovoltaics. [29] Results and Discussion TheoryIn order to understand the loss mechanism and qualify loss factors, we propose the revised detailed balance model, which is expressed as A modified detailed balance model is built to understand and quantify efficiency loss of perovskite solar cells. The modified model captures the light-absorption-dependent short-circuit current, contact and transport-layermodified carrier transport, as well as recombination and photon-recyclinginfluenced open-circuit voltage. The theoretical and experimental results show that for experimentally optimized perovskite solar cells with the power conversion efficiency of 19%, optical loss of 25%, nonradiative recombination loss of 35%, and ohmic loss of 35% are the three dominant loss factors for approaching the 31% efficiency limit of perovskite solar cells. It is also found that the optical loss climbs up to 40% for a thin-active-layer design. Moreover, a misconfigured transport layer introduces above 15% of energy loss. Finally, the perovskit...