With the demonstration of small-area, single-junction polymer solar cells (PSCs) with power conversion efficiencies (PCEs) over the 10% performance milestone, the manufacturing of high-performance large-area PSC modules is becoming the most critical issue for commercial applications. However, materials and processes that are optimized for fabricating small-area devices may not be applicable for the production of high-performance large-area PSC modules. One of the challenges is to develop new conductive interfacial materials that can be easily processed with a wide range of thicknesses without significantly affecting the performance of the PSCs. Toward this goal, we report two novel naphthalene diimide-based, self-doped, n-type water/alcohol-soluble conjugated polymers (WSCPs) that can be processed with a broad thickness range of 5 to 100 nm as efficient electron transporting layers (ETLs) for high-performance PSCs. Space charge limited current and electron spin resonance spectroscopy studies confirm that the presence of amine or ammonium bromide groups on the side chains of the WSCP can n-dope PC71BM at the bulk heterojunction (BHJ)/ETL interface, which improves the electron extraction properties at the cathode. In addition, both amino functional groups can induce self-doping to the WSCPs, although by different doping mechanisms, which leads to highly conductive ETLs with reduced ohmic loss for electron transport and extraction. Ultimately, PSCs based on the self-doped WSCP ETLs exhibit significantly improved device performance, yielding PCEs as high as 9.7% and 10.11% for PTB7-Th/PC71BM and PffBT4T-2OD/PC71BM systems, respectively. More importantly, with PffBT4T-2OD/PC71BM BHJ as an active layer, a prominent PCE of over 8% was achieved even when a thick ETL of 100 nm was used. To the best of our knowledge, this is the highest efficiency demonstrated for PSCs with a thick interlayer and light-harvesting layer, which are important criteria for eventually making organic photovoltaic modules based on roll-to-roll coating processes.

An amino‐functionalized copolymer with a conjugated backbone composed of fluorene, naphthalene diimide, and thiophene spacers (PFN‐2TNDI) is introduced as an alternative electron transport layer (ETL) to replace the commonly used [6,6]‐Phenyl‐C61‐butyric acid methyl ester (PCBM) in the p–i–n planar‐heterojunction organometal trihalide perovskite solar cells. A combination of characterizations including photoluminescence (PL), time‐resolved PL decay, Kelvin probe measurement, and impedance spectroscopy is used to study the interfacial effects induced by the new ETL. It is found that the amines on the polymer side chains not only can passivate the surface traps of perovskite to improve the electron extraction properties, they also can reduce the work function of the metal cathode by forming desired interfacial dipoles. With these dual functionalities, the resulted solar cells outperform those based on PCBM with power conversion efficiency (PCE) increased from 12.9% to 16.7% based on PFN‐2TNDI. In addition to the performance enhancement, it is also found that a wide range of thicknesses of the new ETL can be applied to produce high PCE devices owing to the good electron transport property of the polymer, which offers a better processing window for potential fabrication of perovskite solar cells using large‐area coating method.

The contact between the n-type interlayer and the donor provides an extra interface for charge dissociation.

PSS achieve a high power conversion efficiency (PCE) of 11.35%. Moreover, flexible tandem cells with PCE over 10% are also demonstrated.

With the rapid development of polymer solar cells (PSCs), the manufacture of high-performance large area PSC modules is becoming a critical issue in commercial applications. However, most of the reported light absorption materials and interfacial materials are quite thickness sensitive, with optimal thicknesses of around 100 and 5 nm, respectively. The thickness need to be precisely controlled, otherwise, a small variation in thickness can often lead to a sharp decrease in device performance, especially for interfacial materials. This increases the difficulty of apply these materials in the production of large area PSCs. To avoid the shortcomings of thickness-sensitive materials and achieve high-performance large area PSC modules, we designed and synthesized a series of high mobility donor materials and cathode interfacial materials. These materials exhibited excellent device performance at their optimal thicknesses and maintained high performance even with large thickness variations, thus providing a solution to the bottleneck problem in manufacturing PSC modules and enhancing the device reproducibility. We also developed a simple and efficient approach for achieving a large area cathode interlayer with controlled film composition, uniformity, and thickness at the nanometer-scale using an electrostatic layer-by-layer self-assembly (eLbL) process. The eLbL films exhibited excellent cathode modification ability and can be integrated into the current large area device processing techniques. Thus, our approaches from both material design to device engineering provide new solutions for preparing high-performance large area PSC modules.

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both the top and bottom electrodes. These semitransparent PSCs (ST-PSCs) could be used as power generating windows and aesthetic architectural glasses, which are considered as the most appealing photovoltaic product for building integrated photovoltaic applications. [12][13][14][15][16][17][18] However, unlike opaque PSCs, the overall performance of ST-PSCs depends not only on the PCE but also the average visible transmittance (AVT) and color rendering properties. [19] Therefore, the great challenge for ST-PSCs is to achieve high PCE yet with good AVT and color rendering properties.Optimization of both the PCE and AVT in ST-PSCs is inherently challenging as these two performance parameters are difficult to optimize at the same time. The ideal optical condition for ST-PSC can be reached when the light passes through the device is only absorbed by the active layer but not the other layers such as the transparent electrodes and the interlayers, which allows the maximal amount of light transmitted through the devices. The ideal electronic condition for ST-PSC fulfilled if all the photons absorbed by the light harvesting layer can be dissociated and collected to generate photocurrent with internal quantum efficiency equal to 100%. [20] However, in real cases, the optical and electronic properties of the ST-PSCs are strongly affected by the choice of interlayers and transparent electrodes. For example, the interlayer not only can act as a charge selective layer to improve charge extraction in PSCs but also can act as an optical spacer that alters the optical field distribution within the device. [21] Depending on the choice of the transparent conductive material used for constructing the transparent electrode, it can be categorized as nonreflective or semireflective one. The latter case, which can be fabricated using ultrathin metal films (UTMFs) with the reflectance and transmittance depending on the thickness of the metal films, is of particular interest as it provides better flexibility in tuning the optical property of ST-PSCs. [22,23] However, the deposition of high quality and smooth UTMF, which is a prerequisite for achieving high transparency and conductivity, as top transparent conducting electrode for ST-PSCs is not straight forward and the film quality is strongly depending of the choice of underneath charge transport layer and deposition conditions. [24][25][26] In previous reports, tailored charge transport layers, such as a C 60 surfactant as electron transport layer (ETL) and MoS 2 as hole transport layer, had been In this study the thickness of the PTB7-Th:PC 71 BM bulk heterojunction (BHJ) film and the PF3N-2TNDI electron transport layer (ETL) is systematically tuned to achieve polymer solar cells (PSCs) with optimized power conversion efficiency (PCE) of over 9% when an ultrathin BHJ of 50 nm is used. Optical modeling suggests that the high PCE is attributed to the optical spacer effect from the ETL, which not only maximizes the optical field within the BHJ film but also facilitates the formation of a...

We report a series of counterion-tunable n-type conjugated polyelectrolytes for the interface engineering of polymer solar cells.