Corrosive ionic defects in perovskite films degrade perovskite solar cells (PSCs) and long-term stable PSCs are realized by neutralizing the defects.

Despite the recent unprecedented increase in the power conversion efficiencies (PCEs) of small-area devices (≤0.1 cm ), the PCEs deteriorate drastically for PSCs of larger areas because of the incomplete film coverage caused by the dewetting of the hydrophilic perovskite precursor solutions on the hydrophobic organic charge-transport layers (CTLs). Here, an innovative method of fabricating scalable PSCs on all types of organic CTLs is reported. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, fabricating uniform perovskite films on large-area substrates (18.4 cm ) and PSCs with the total active area of 6 cm (1 cm × 6 unit cells) via a single-turn solution process is successfully demonstrated. All of the unit cells exhibit highly uniform PCEs of 16.1 ± 0.9% (best PCE of 17%), which is the highest value for printable PSCs with a total active area larger than 1 cm .

The importance of interfacial engineering as a new strategy for improving the power conversion efficiencies (PCEs) of planar-heterojunction (PHJ) perovskite solar cells is highlighted by incorporating sol–gel ZnO modified with PCBM.

into the ITO electrode. [5][6][7][8] One of the promising ETLs is a class of materials known as solution-based metal oxide systems, such as titanium sub-oxide (TiO x ) and zinc oxide (ZnO). Because such metal oxides have specifi c energy levels to only transfer electrons, their operation as ETLs is compatible with their excellent electron-transporting and hole-blocking characteristics. [ 2,3,9,10 ] Numerous synthetic processes have been developed for those metal oxide systems. In particular, sol-gel synthesis of those metal oxide systems has received intense attention because of its simple solution process for uniform fi lm formation at room temperature (RT). When sol-gel processed TiO x (or ZnO) is coated between ITO and the BHJ layer, the layer acts as an ETL in i-PSCs by aligning energy levels and selecting only electron transport. However, because of the low carrier density or the many trap sites in the semiconducting metal oxide, a Schottky barrier develops at the high WF-metal/metal-oxide interface or energy level mismatching at the metal oxide/BHJ layer interface becomes a recurring issue. [9][10][11][12][13][14][15] Those problems hinder the electron transport between the BHJ layer and ITO and result in the extremely low device performance in i-PSCs, as shown in Figure 1 a. [9][10][11][12]14,15 ] Although photo-excitation of the metal oxides by UV-irradiation increases the carrier density in the metal oxides and recovers the device performance by narrowing and lowering the depletion barrier, as in Figure 1 b, through a so-called a "lightsoaking process," such a photoreduction process takes several minutes and the absence of UV light irradiation (for example, UV protection coating etc.) would be critical for practical applications. [9][10][11][12][13][14][15] Although many researchers have tried to fi nd a fundamental solution to remove the light-soaking process of the metal oxides in the i-PSCs, there has been no successful approach that is directly applicable to printable photovoltaics.The light-soaking process in i-PSCs with the TiO x ETL implies that the increased carrier density in TiO x by chemical doping can be a fundamental solution for this problem. In general, doping the titanium oxide system precedes the reduction process, for example nitrogen (N) doping of titanium dioxide (TiO 2 ). When titanium-oxygen (Ti-O) bonds are replaced with the titanium-nitrogen (Ti-N) bonds, it is well known that the carrier density of TiO 2-δ N δ substantially increases. [16][17][18][19] However, because the formation of the Ti-O bonds is a predominant process in the typical sol-gel method, it has been impossible to control the doping process in the sol-gel fabrication of the metal oxide systems. [ 18,[20][21][22] Such a diffi culty in the doping process often requires additional purifi cations of the sol-gel processed metal oxides, for example, washing or heating processes. [ 18,[21][22][23] Bulk heterojunction (BHJ) polymer solar cells (PSCs) continue to be a promising approach for low-cost energy harvesting becau...

The inferior long-term stability of polymer-based solar cells needs to be overcome for their commercialization to be viable. In particular, an abrupt decrease in performance during initial device operation, the so-called 'burn-in' loss, has been a major contributor to the short lifetime of polymer solar cells, fundamentally impeding polymer-based photovoltaic technology. In this study, we demonstrate polymer solar cells with significantly improved lifetime, in which an initial burn-in loss is substantially reduced. By isolating trap-embedded components from pristine photoactive polymers based on the unimodality of molecular weight distributions, we are able to selectively extract a trap-free, high-molecular-weight component. The resulting polymer component exhibits enhanced power conversion efficiency and longterm stability without abrupt initial burn-in degradation. Our discovery suggests a promising possibility for commercial viability of polymer-based photovoltaics towards real solar cell applications.

Highly efficient P-I-N type perovskite/bulk-heterojunction (BHJ) integrated solar cells (ISCs) with enhanced fill factor (FF) (≈80%) and high near-infrared harvesting (>30%) are demonstrated by optimizing the BHJ morphology with a novel n-type polymer, N2200, and a new solvent-processing additive. This work proves the feasibility of highly efficient ISCs with panchromatic absorption as a new photovoltaic architecture and provides important design rules for optimizing ISCs.

A new film‐casting method for polymer electrodes is reported, in which thickness‐controlled drop‐casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin‐casting and drop‐casting methods, and by rigorously controlling the film formation parameters, flexible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness‐independent conductivities of ∼600 S cm−1 down to a film thickness of 0.2 μm, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method significantly reduced the sheet resistance (∼90 Ω/square) of the PANI:CSA electrodes compared with the conventional spin‐cast films, enhancing the performance of the devices deposited on plastic substrates. The flexible polymer light‐emitting diode produced a brightness of 6000 cd m−2, and the flexible polymer solar cell exhibited a power conversion efficiency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin‐casting method.

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