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Conventional photodetectors are usually "color blind" and require additional dispersive components or complicated structures to recognize colors. In this work, an organic photodetector (OPD) is designed with a layer of molybdenum(VI) oxide (MoO3) stacked on an organic donor/acceptor charge transfer interface. The band structure of the OPD is designed with multiple charge separation channels that can be activated/deactivated under reverse and forward biases. The combination of a high or low photocurrent under reverse and forward biases determines the colors of the received light, and that forms the heart of "non-color blind" ability to recognize light colors in the OPD. The energy structure and charge collection pathways in the OPD are investigated with biased external quantum efficiency (EQE), ultraviolet photoelectron spectroscopy (UPS) and current density–voltage (J–V) studies. The OPD with the ability of color and wavelength determination demonstrates its potential to recognize colors without using additional components and the dual mode operation enables it to work under different conditions via switching its detection ranges with bias voltages. This design principle can be utilized to fabricate multifunctional devices by simply selecting different donor–acceptor materials according to the desired detection ranges. [ABSTRACT FROM AUTHOR]

Charge extraction efficiency is one of the key factors to determine the performance of solar cells, which depends on the electronic properties of the electron and hole transporting layers. Sol–gel derived NiOx as the hole transporting layer (HTL) used in perovskite solar cells (PVSCs) promises both low-cost and high-stability. However, current NiOx based PVSCs have a relatively low fill factor (FF) and device efficiency. Here, we show that using an oxide composite approach by incorporating thermally reduced graphene oxide (rGO) into the NiOx layer (NiOx:rGO) can effectively improve the film conductivity without sacrificing its high work function. The improved charge extraction efficiency reduces the interfacial recombination loss and increases the carrier lifetime in NiOx:rGO based PVSCs, which are evidenced by transient photocurrent and transient photovoltage measurements. The NiOx:rGO based PVSC achieves a promising PCE of 19.1% with a significantly improved FF from 73% to 81% compared to the device using solely NiOx. Moreover, the NiOx:rGO based PVSC shows a decent photo-stability tracked at the maximum-power-point and a long shelf-lifetime with negligible degradation in device performance after 70 days. It is believed that the oxide composite transporting layer would be a promising alternative to further develop highly efficient and stable PVSCs. [ABSTRACT FROM AUTHOR]

A porphyrin-based donor material P1 is used to fabricate bulk-heterojunction solar cells harvesting room light. P1 consists of a porphyrin ring linked by two ethylrhodanine end caps via phenylene ethynylene bridges. Organic photovoltaic (OPV) cells using P1 as the donor exhibit significantly improved performances under indoor illumination compared to 1 sun conditions. For P1:PC71BM cells, an optimized-PCE of 19.2% was achieved under a 300 lux illumination of a 3000 K LED tube. Besides high PCEs, the porphyrin-based devices also exhibit enhanced OPV performances in thick film regions (∼200 nm) compared to a control BHJ cell using PCDTBT:PC71BM. The thick-film P1-based device shows an overall PCE of 18.2%. The origins of the thickness independent OPV performances were examined, and they can be attributed to the low electronic disorders of these materials when compared to their polymer counterparts. [ABSTRACT FROM AUTHOR]

Mixed-organic-cation FA1−xMAxPbI3 perovskites are currently attracting intensive attention for their high photovoltaic performance. However, FA1−xMAxPbI3 usually has an undesired non-perovskite phase leading to a compromised efficiency, and a facile strategy to achieve pure-phase FA1−xMAxPbI3 has been rarely reported. Here, we demonstrate a facile approach to form δ-phase free FA1−xMAxPbI3 using a non-stoichiometric precursor solution. It is found that a small amount of excess methylammonium iodide (MAI) added to the precursor solution has a profound effect on perovskite crystallization during the liquid-to-solid phase transformation. Using an in situ photoluminescence spectroscopy measurement, it is found that the excess MAI can promote the formation of FA1−xMAxPbI3 and facilitate the cation-exchange between organic FA+ and MA+ during the film formation. Based on the optimized pure-phase FA1−xMAxPbI3, the perovskite solar cells exhibit an encouraging power conversion efficiency (PCE) of 17.40%. This study demonstrates a facile method to achieve high performance FA dominating mixed-organic-cation perovskite devices while providing insight into the ion-exchange process during perovskite crystallization. [ABSTRACT FROM AUTHOR]

Developing facile strategies that enable high-performance perovskite solar cell (PSC) fabrication in ambient air is appealing yet challenging for low-cost and large-scale industrial deployment. However, attempts in this regard are still limited to methylammonium lead triiodide (CH3NH3PbI3), which lags significantly behind the rapid development of the state-of-the-art formamidinium (FA) based mixed perovskites. Here, a PbI2–(CsI)0.15–(FAI)x intermediate complex is proposed to unlock the processing limitation and efficiently facilitate the growth of high-quality mixed-cation Cs0.15FA0.85PbI3 perovskite films in ambient air with relative humidity (RH) as high as 70 ± 10%. It is found that the PbI2–(CsI)0.15–(FAI)x (x = 0.2 to 0.4) intermediate complex consisting of a mixture of composites is favorable for the conversion of PbI2 to high-quality Cs0.15FA0.85PbI3 perovskite. Eventually, it reduces the required FAI concentration deposited on the intermediate for the conversion of PbI2 to perovskite, which allows the strong hygroscopic FAI to be processed in ambient air. With the PbI2–(CsI)0.15–(FAI)0.3 intermediate complex, a low-temperature air-processed planar Cs0.15FA0.85PbI3 PSC achieves a champion power conversion efficiency (PCE) of 15.56% with superior thermal-stability and photo-durability, demonstrating its great potential for the large scale development of PSCs. [ABSTRACT FROM AUTHOR]

In recently developed high-efficiency metal organometal halide perovskite solar cells (PVSCs), electron and hole transporting materials have shown key roles in determining the growth of perovskite crystals, as well as the performance and stability of the device. However, interlayer materials which can facilitate both high efficiency and stability at low cost are still limited. Here, we demonstrate that, by controlling the thickness of solution-processed graphene oxide (GO), one can achieve a balance of high work function and conductivity. Using GO with the optimized thickness as a hole-transporting material (HTM) in PVSCs, a high power conversion efficiency (PCE) of 16.5% with no hysteresis has been achieved with excellent light-soaking photocurrent stability in comparison with a commonly used organic-based HTM. Under high humidity and continuous light soaking, the encapsulated perovskite devices retained ＞80% of their initial efficiency for ＞2000 h. Detailed studies on the GO binding energy, charge transfer efficiency with perovskite, and crystal morphology shed light on the origin of the observed improvement in photovoltaic performance. Benefiting from the merits of low temperature, solution processability and low cost, the proposed GO fabrication methods could aid scalable production of PVSCs with high PCE and excellent stability. [ABSTRACT FROM AUTHOR]

Regio-random (P1) and -regular (P2) difluorobenzene-naphthalene-containing polymer acceptors were developed for bulk-heterojunction all-polymer solar cells (all-PSCs). P2 exhibited significantly higher crystallinity in thin films, providing high spectral absorptivity and electron mobility than P1. When used in all-PSC devices, P2 afforded a respectably higher power conversion efficiency of over 5%. [ABSTRACT FROM AUTHOR]

The origin of the impact of mobile ions in perovskite solar cells (PVSCs) has recently become a hot topic of debate. Here, we investigate systematically the structural effect and various recombination pathways in PVSCs with different ion concentrations. By probing the transient ionic current in PVSCs, we extract mobile ion concentrations in a range of 1016 cm−3 to 1017 cm−3 depending on the processing conditions during a two-step process. The PVSC with the lowest ion concentration has both the highest efficiency over 15% and shelf-life over 1300 hours. Interestingly, in contrast to the commonly adopted models in the literature, we find that the crystal size and the bimolecular and trap-assisted recombination are not responsible for the large difference in photovoltaic performance. Instead, by using transient photocurrent and steady-state photoluminescence approaches, we find that the large reduction of short-circuit current (Jsc) in mobile ion populated devices is ascribed to the slow decay in photocurrent and the increasing amount of non-radiative recombination. In addition, we also find that the excess mobile ions trigger the deformation of perovskite to PbI2, which severely reduces the device lifetime. The results provide valuable information on the understanding of the role of excess mobile ions in the degradation mechanism of PVSCs. [ABSTRACT FROM AUTHOR]

Solution processed metal–organic halide perovskite photovoltaic devices have recently drawn tremendous attention due to their simplicity of fabrication and high efficiency. Despite numerous reports on optimizing perovskite films with different fabrication approaches, there is limited understanding on the correlation between sensitive processing conditions and the microstructural and electronic properties of perovskite films. Here we combine several opto-electrical spectroscopy techniques to investigate the methylammonium iodide (MAI) loading time effect on the doping density profile and uncoordinated ions in resulting CH3NH3PbI3 perovskite thin films. We find that even in a very short period of different loading times within two minutes, there is a significant impact on the device power conversion efficiency (PCE) from 2% to over 15%. It is found that the doping density profile is inhomogeneous across the perovskite film with too short MAI loading time, resulting in an S-shape in the current density–voltage (J–V) characteristics. On the other hand, devices with too long loading time have excess uncoordinated ions attributed to the J–V hysteresis. By using combined spectroscopy techniques to pinpoint the electronic properties in perovskite films, this work would shed light on the understanding of the controversial origins of the reported S-shape and hysteresis in perovskite photovoltaic cells. [ABSTRACT FROM AUTHOR]

Two newly synthesized naphthodithiophene-based copolymers, PNB, exhibit a low optical bandgap of ∼1.64 eV with which the solar cells fabricated from the blend of PNB and PC71BM afforded a power conversion efficiency of 5.3% with external quantum efficiency over 60% in a broad spectral range. [ABSTRACT FROM AUTHOR]

A new benzodithiophene-based copolymer PTG1 with dithienylbenzothiadiazole–vinylene side chains exhibits excellent film-forming ability, a deep HOMO energy level, and a good miscibility with PC71BM. Bulk heterojunction polymer solar cells fabricated from PTG1 and PC71BM showed a promising power conversion efficiency over 4.0%. [ABSTRACT FROM AUTHOR]

Photodetectors (PDs) based on organic materials exhibit potential advantages such as low-temperature processing, and superior mechanical properties and form factors. They have seen rapid strides toward achieving performance metrics comparable to inorganic counterparts. Here, a simplified device architecture is employed to realize stable and high-performance organic PDs (OPDs) while further easing the device fabrication process. In contrast to the sequential deposition of the hole blocking layer (HBL) and active layer (conventional 'two-step' processing), the proposed strategy forms a self-assembled HBL and active layer in a 'single-step' process. A high-performance UV-Vis-NIR OPD based on the PM6:BTP-eC9 system is demonstrated using this cost-effective processing strategy. The green solvent processed proof-of-concept device exhibits remarkable responsivity of ∼0.5 A W -1 , lower noise current than conventional two-step OPD, ultrafast rise/fall times of 1.4/1.6 μs (comparable to commercial silicon diode), and a broad linear dynamic range of 140 dB. Importantly, highly stable (light and heat) devices compared to those processed by the conventional method are realized. The broad application potential of this elegant strategy is proven by demonstrating the concept in three representative systems with broadband sensing competence.