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The low cost and scalability advantages of printable mesoscopic perovskite solar cells (p‐MPSCs) are impaired by the issue of limited power conversion efficiency (PCE). Herein, the PCE of p‐MPSCs is improved by introducing the polymer additive polyacrylonitrile (PAN) into the formamidinium (FA)‐based perovskite for crystallization and defect modulation. PAN forms hydrogen bond and coordination bond with halide perovskite through its C≡N group. Such interactions improve the crystallization and filling of FA‐based perovskite in the mesoscopic scaffold and bring a long carrier lifetime by passivating defects. The synergy improves the PCE of p‐MPSCs from 16.80% to 18.33%. Meanwhile, the hydrophobic nature of PAN enhances the device's resistance against moisture. This work demonstrates that the polymer additive is a promising choice for breaking the PCE limit of p‐MPSCs. [ABSTRACT FROM AUTHOR]

The organic–inorganic halide perovskite solar cells (PSCs) are rapidly developed in just a few years due to its high power conversion efficiency. However, it still faces some critical issues, one of which is the presence of toxic lead (Pb2+). Recent researches show that barium (Ba2+) can partially replace the Pb2+ in perovskite structure and achieve a promising device performance because of its adequate ionic radius. However, the optimal replacement amount of Ba2+ in perovskite is still limited. Herein, the methylammonium (MA)/formamidinium (FA) mixed‐cation perovskite is used as the active layer in PSCs and Pb2+ is partially substituted with Ba2+. Compared with the pure MA system, the best device efficiency can be achieved using higher Ba2+ replacement ratio. In addition, while introducing the appropriate polymer additive, the replacement ratio can be further increased without compromise of device efficiency. Using polyethylene glycol as polymer additive, 10.0 mol% Ba‐doped MA/FA mixed‐cation PSC with an efficiency of 16.1% can be realized. It is believed that this report provides an effective strategy to fabricate high‐performance lead‐reduced PSCs. [ABSTRACT FROM AUTHOR]

Abstract: The role of a tertiary polymer‐based additive is investigated in increasing the efficiency of inverted low bandgap polymer:fullerene bulk heterojunction (BHJ) solar cells. Charge separation in polymer BHJ solar cells relies on the phase separation between electron accepting fullerene derivatives and photoactive polymers. Proper distribution of individual phases of suitable crystallinities within the active layer is a key factor for efficient charge transport/extraction and high photovoltaic performance. Here, it is demonstrated that the minor addition of a tertiary amorphous polymer, polystyrene (PS), with optimized molecular weights can increase the overall photovoltaic efficiency of poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)]:phenyl‐C61butyric acid methyl ester (PCDTBT:PCBM) inverted BHJ solar cells, through the interfacial‐tension‐driven increase in crystallinities of photoactive phases and redistribution of PCBM molecules away from the top hole‐collecting anode interface. Complementary studies correlating polymer interfacial tension, blend internal structure, charge transport, and photovoltaic characteristics show that tertiary, high molecular‐weight polymers can serve as effective additives for improving the performance of low bandgap polymer solar cells. [ABSTRACT FROM AUTHOR]

Interfaces between the photoactive layers and electrodes play critical roles in controlling the performance of optoelectronic devices. Herein, a novel nonconjugated polymer additive (nPA), poly(2-vinylpyridine) (P2VP), is reported for modifying the interfaces between the bulk-heterojunction (BHJ) and cathode/metal oxide (MO) layers. The P2VP nPA enables remarkably enhanced power conversion efficiencies (PCEs) and ambient stability in different types of polymer solar cells (PSCs). Importantly, interfacial engineering can be achieved during deposition of the P2VP nPA-containing BHJ active layer via simple, one-step solution processing. The P2VP nPA has much higher surface energy than the BHJ active components and stronger interaction with the surface of MO, which affords spontaneous vertical phase separation from the BHJ layer on the MO surface by one-step solution processing. The self-assembled P2VP layer substantially reduces the work function and surface defect density of MO, thereby minimizing the charge-extraction barrier and increasing the PCEs of the PSCs significantly, i.e., PTB7-Th:PC71BM (10.53%→11.14%), PTB7:PC71BM (7.37%→8.67%), and PTB7-Th:P(NDI2HD-T) all-PSCs (5.52%→6.14%). In addition, the lifetimes of the PSCs are greatly improved by the use of the P2VP nPA. [ABSTRACT FROM AUTHOR]

Three low-cost propeller-shaped small molecules based on a triphenylamine core and the high-performance donor molecule 7,7′-[4,4-bis(2-ethylhexyl)-4 H-silolo[3,2- b:4,5- b′]dithiophene-2,6-diyl]bis[6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[ c][1,2,5]thiadiazole] (DTS(FBTTh2)2) were investigated as hole-transporting materials in perovskite solar cells. Each hole-transporting material was designed with highly modular side arms, allowing for different bandgaps and thin-film properties while maintaining a consistent binding energy of the highest occupied molecular orbitals to facilitate hole extraction from the perovskite active layer. Perovskite solar cell devices were fabricated with each of the three triphenylamine-based hole-transporting materials and DTS(FBTTh2)2 and were compared to devices with 2,2′,7,7′-tetrakis( N, N-di- p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) hole-transporting layers. Each of our triphenylamine hole-transporting materials and DTS(FBTTh2)2 displayed surface morphologies that were considerably rougher than that of spiro-OMeTAD; a factor that may contribute to lower device performance. It was found that using inert, insulating polymers as additives with DTS(FBTTh2)2 reduced the surface roughness, resulting in devices with higher photocurrents. [ABSTRACT FROM AUTHOR]

In article number 1602812, Jung‐Yong Lee, Bumjoon J. Kim, and co‐workers investigate nonconjugated polymer additives (nPAs) for highly efficient and stable polymer solar cells (PSCs). The P2VP nPA self‐assembles vertically on the ZnO surface via a single coating process for the deposition of active materials. The self‐assembled P2VP reduces the work function and surface defect density of ZnO, which leads to efficient and stable PSCs with up to 11.14% efficiency. [ABSTRACT FROM AUTHOR]