is drinking coffee.'' The perfect temperature to serve coffee is 85 C. The authors here introduced caffeine, which is the active material of coffee, into the active materials of the perovskite solar cells to enhance their performance and thermal stability under 85 C. A champion-stabilized efficiency of 19.8% with 1,300 h thermal stability at 85 C in nitrogen was achieved. This simple, costeffective, and generalized strategy increases the commercial prospects of perovskite solar cells.

Halide perovskite films processed from solution at low‐temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo‐crosslinked [6,6]‐phenylC61‐butyric oxetane dendron ester (C‐PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI3) perovskite films. Also, it is demonstrated that C‐PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI3. Thus, MAPbI3 perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI3 on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.

also the multiple exciton generation phenomenon, specific to CQDs, opens an avenue to make full utilization of solar radiation. [5][6][7] Recently, halide perovskite CQDs have emerged as a new class of CQDs for photovoltaics, offering compelling combination of the advantages of traditional CQDs and exceptional properties of halide perovskite materials, such as the desirable bandgap, high absorption coefficient, and defect tolerance. [8][9][10] Furthermore, the perovskite CQDs, such as CsPbI 3 and formamidinium lead iodide (FAPbI 3 ), were reported to show superior phase stability over their bulk form owing to the size-induced lattice strain and enhanced contribution from the surface energy. [11,12] Accordingly, the CQD solar cells based on the perovskite material have demonstrated a great potential with a record power conversion efficiency (PCE) as high as 13% along with excellent operational stability. [12,13] Although perovskite materials display superior optoelectronic properties to the conventional semiconductors, the low charge carrier separation efficiency, which is one of the critical obstacles toward higher performance of traditional CQD devices, still remains in the perovskite CQD solar cells. [14] While exciton binding energies (E b ) of bulk perovskite materials were measured to be as low as few millielectronvolts, facilitating spontaneous generation of free carriers at room temperature, [15] the E b of the perovskite CQD was estimated to be significantly higher (up to ten times) than that of the bulk counterparts. [9,16] As a result, the photogenerated charge carriers in the CQD films are subjected to be lost through recombination before being extracted to selective contact layers. [17] Therefore, promoting effective charge separation to reduce recombination becomes a crucial factor for boosting the PCE of the perovskite CQD solar cells.In order to facilitate such charge separation process and thus reduce the charge recombination in conventional CQD solar cells, a lot of efforts have been developed, such as coreshell structural design, surface ligand modification, and device structure engineering. [18][19][20][21][22][23] These available strategies employed in the traditional CQDs devices, however, are still not compatible with perovskite CQD system owing to their vulnerable structural stability as well as absence of well-established Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher-performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type-II core-shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surfac...

No abstract

With the rapid development of the Internet of Things (IoTs), photovoltaics (PVs) has a vast market supply gap of billion dollars.

A novel biphenyl fumaronitrile as an acceptor and triphenylamine as donor conjugated building blocks are used for the first time to successfully synthesize donor–acceptor–donor molecule (D‐A‐D) 2,3‐bis(4′‐(bis(4‐methoxyphenyl)amino)‐[1,1′‐biphenyl]‐4‐yl)fumaronitrile (TPA‐BPFN‐TPA). The new TPA‐BPFN‐TPA with low‐lying HOMO is used as a dopant‐free hole‐transporting material (HTM) in mesoporous perovskite solar cells. The performance of the solar cells using this new HTM is compared with the traditional 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamino)‐ 9,9′‐spirobifluorene (Spiro‐OMeTAD) HTM based devices for outdoor and indoor performance evaluation. Under 1 sun illumination, dopant‐free TPA‐BPFN‐TPA HTM based devices exhibit a power conversion efficiency (PCE) of 18.4%, which is the record efficiency to date among D‐A‐D molecular design based dopant‐free HTMs. Moreover, the stability of unencapsulated TPA‐BPFN‐TPA‐based devices shows improvement over Spiro‐OMeTAD‐based devices in harsh relative humidity condition of 70%. Another exciting feature of the newly developed HTM is that the TPA‐BPFN‐TPA‐based devices exhibit improved PCE of 30% and 20.1% at 1000 lux and 200 lux illuminations, respectively. This new finding provides a solution to fabricate low indoor (low light) and outdoor (1 sun) perovskite solar cell devices with high efficiency for cutting‐edge energy harvesting technology.

A maximum power conversion efficiency of 17.21% was achieved in CH3NH3PbIxCl3−x:-C-PCBSD based solar cells with improved perovskite crystallization.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approachtreating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxideto induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.