Qingshun Dong

Hole-Conductor-Free, Metal-Electrode-Free TiO2/CH3NH3PbI3 Heterojunction Solar Cells Based on a Low-Temperature Carbon Electrode

Low cost, high efficiency, and stability are straightforward research challenges in the development of organic-inorganic perovskite solar cells. Organolead halide is unstable at high temperatures or in some solvents. The direct preparation of a carbon layer on top becomes difficult. In this study, we successfully prepared full solution-processed low-cost TiO2/CH3NH3PbI3 heterojunction (HJ) solar cells based on a low-temperature carbon electrode. Power conversion efficiency of mesoporous (M-)TiO2/CH3NH3PbI3/C HJ solar cells based on a low-temperature-processed carbon electrode achieved 9%. The devices of M-TiO2/CH3NH3PbI3/C HJ solar cells without encapsulation exhibited advantageous stability (over 2000 h) in air in the dark. The ability to process low-cost carbon electrodes at low temperature on top of the CH3NH3PbI3 layer without destroying its structure reduces the cost and simplifies the fabrication process of perovskite HJ solar cells. This ability also provides higher flexibility to choose and optimize the device, as well as investigate the underlying active layers.

Low-Temperature and Solution-Processed Amorphous WO(x) as Electron-Selective Layer for Perovskite Solar Cells.

The electron-selective layer (ESL) is an indispensable component of perovskite solar cells (PSCs) and is responsible for the collection of photogenerated electrons. Preparing ESL at a low temperature is significant for future fabrication of flexible PSCs. In this work, solution-processed amorphous WO(x) thin film was prepared facilely at low temperature and used as ESL in PSCs. Results indicated that a large quantity of nanocaves were observed in the WO(x) thin film. In comparison with the conventional TiO2 ESL, the WO(x) ESL exhibited comparable light transmittance but higher electrical conductivity. Compared with the TiO2-based PSCs, PSCs that use WO(x) ESL exhibited comparable photoelectric conversion efficiency, larger short-circuit current density, but lower open-circuit voltage. Electrochemical characterization indicated that the unsatisfied open-circuit voltage and fill factor were caused by the inherent charge recombination. This study demonstrated that this material is an excellent candidate for ESL.

Interlaced W18O49 nanofibers as a superior catalyst for the counter electrode of highly efficient dye-sensitized solar cells

Sufficient contact, high catalytic activity, free electron transport and ionic diffusion are desired for liquid–solid heterogeneous electrocatalysis. However, preparing catalysts that simultaneously possess all of these four advantages has proven challenging. Nanostructures originating from anisotropic growth always exhibit specific structural advantages and unique physical, chemical or catalytic properties. Herein, via a facile and template-free solvothermal approach, we synthesized W18O49 nanofibers (NFs) and nanofiber bundles (NFBs), as well as hierarchical spheres (HSs). As catalyst for the counter electrode (CE) of dye-sensitized solar cells (DSCs), W18O49 NFs demonstrated remarkable electrocatalytic activity because: (i) abundant oxygen vacancies offered sufficient active sites for reduction of I3− into I−; (ii) the one dimensional NFs were more beneficial to electron transport; (iii) the two phases, the liquid electrolyte and the solid NFs, could fully contact each other, and meanwhile ions could diffuse freely among the networks constructed by the interlaced NFs. Notably, DSCs using the NF-based semitransparent CE achieved high photoelectric conversion efficiencies (PCEs) up to 8.58%, superior to those based on NFBs or HSs, and comparable to that of 8.78% using Pt as the CE. Furthermore, it was proven that both the electrolytic activity and the PCE deteriorated drastically when the NFs were destroyed. Our work here will be of great interest for both fundamental research and practical applications of W18O49 nanomaterials in other fields.

High electrocatalytic activity of W18O49 nanowires for cobalt complex and ferrocenium redox mediators

Understanding the relationship between the surface of electrocatalysts and the catalytic properties of different redox mediators is beneficial to the rational design of efficient catalysts for use in practical catalytic processes. Previous research observed that surface oxygen vacancies (SOVs) affected the catalytic activity for triiodide/iodide (I−/I3−) and T2/T− (T− = 5-mercapto-1-methyltetrazole ion) redox mediators in dye-sensitized solar cells (DSCs). However, the electrocatalytic properties of larger and steric metal complex redox mediators (cobalt complex, ferrocenium) on SOVs of W18O49 are unclear and have never been reported. In this study, we investigated the electrocatalytic properties of cobalt complex and ferrocenium redox mediators on SOVs of W18O49. Results indicated that the catalytic performance of W18O49 nanowires (NWs) as a counter electrode for cobalt complex and ferrocenium redox mediators was comparable to that of Pt. After SOVs filling, the reduction reaction activity of the cobalt complex decreases slightly whereas it increases slightly for ferrocenium. These findings enrich our understanding of heterogeneous catalytic reactions on the surface of transition metal complexes for different redox mediators.

Flexibly assembled and readily detachable photovoltaics

Is it possible that one day flexible assembly, repeated detachment, facile repair and maintenance will all be realized for photovoltaic devices? Our work provides a feasible strategy. A flexibly assembled and readily detachable stacking perovskite solar cell (S-PSC) consisting of two individual half cells is reported for the first time. High adaptability to various electrode substrates is demonstrated, which endows S-PSCs with promising prospects in future manufacture and applications. Considering that a robust interface between two half cells is an essential precondition for repeated detachment, a series of interfacial modifications are conducted and eventually considerable power conversion efficiencies (PCEs) of up to 14.62% are attained. Meanwhile, the S-PSCs can withstand repeated assembly and disassembly tests more than 100 times without a decline in the PCE. This work charts a new path for future innovative design of solar cells featuring flexible and facile production, storage, and cost-effective repair and maintenance.

Rational design of SnO 2 -based electron transport layer in mesoscopic perovskite solar cells: more kinetically favorable than traditional double-layer architecture

Here, the interfacial synergism of discontinuous spot shaped SnO2 and TiO2 mesoporous nanocomposite as electron transfer layer (ETL) underlayer is presented in highly efficient mesoscopic perovskite solar cells (M-PSCs). Based on this new strategy, strong charge recombination observed in previous SnO2-based ETLs is suppressed to a great extent as the pathways of charge recombination and energy loss are blocked effectively. Meanwhile, the internal series resistance of entire M-PSC is decreased remarkably. The new ETL is more kinetically favorable to electron transfer and thus results in significant photovoltaic improvement and alleviated hysteresis effect of M-PSCs.摘要本文采用点分布SnO2和TiO2介孔层中的纳米粒子组成的“协同层”作为高效介孔钙钛矿太阳能电池的电子传输层衬层. 基于该新策略, 电荷复合和能量损失路径被有效阻隔, 使得之前报道的SnO2基电子传输层介孔钙钛矿太阳能电池中的强烈电荷复合被有效抑制. 同时, 整个介孔钙钛矿太阳能电池的串联电阻显著降低. 新型的电子传输层动力学上更有利的电子传输有效提升了介孔钙钛矿太阳能电池的光伏性能, 并明显抑制了电池的回滞.

Tailoring electrical property of the low-temperature processed SnO 2 for high-performance perovskite solar cells

Herein, we for the first time doped Nb5+ into the low-temperature (<100°C) SnO2 sol-gel route to tailor the electrical property of SnO2 layers and the band alignment between SnO2 and the normally used mixed perovskites. The results revealed that proper Nb5+ doping increased the conductivity of the SnO2 electron transport layer (ETL), and the conduction band (CB) level of the SnO2 ETL was shifted down to approach the CB level of perovskites, which facilitated the electron injection from perovskite to SnO2, accelerated the charge transport, and reduced the non-radiative recombination, leading to improved power conversion efficiency from 18.06% to 19.38%. The Nb5+ doping process provided an efficient route for fabricating high-efficiency perovskite solar cells (PSCs) at a temperature lower than 100°C, and promoted the commercialization progress of PSCs.摘要本文中我们首次在低温(<100°C)SnO2溶胶-凝胶中通过掺杂Nb5+调控SnO2电学性质, 使SnO2与混合离子钙钛矿之间形成更匹配的能级. 掺杂Nb5+后SnO2电子传输层导电率明显提升, 导带位置下移更加接近混合离子钙钛矿导带, 有效促进了电子由SnO2向钙钛矿层的注入, 并加速了电子传输过程, 二者的共同作用使非辐射复合几率降低, 器件效率由18.06%提升至19.38%. Nb5+掺杂SnO2为低温(<100°C)制备高效率钙钛矿太阳能电池提供了有效参考途径, 有望进一步推动钙钛矿太阳能电池的产业化进程.

Room-temperature solution-processed amorphous NbOx as an electron transport layer in high-efficiency photovoltaics

Preparation of high-quality amorphous oxide semiconductor (AOS) films by wet chemical routes at low temperature (<100 °C) remains difficult. Here, we conducted systematic research for the low-temperature fabrication of AOS by a solution route using amorphous NbOx as an example. Perovskite solar cells (PSCs) based on a solution-processed amorphous ETL obtain a high power conversion efficiency of up to 19.09%, which is much higher than that of the PSCs using solution-processed AOS ETLs and even compare favourably with those using vacuum-processed ETLs.

High-air-flow-velocity assisted intermediate phase engineering for controlled crystallization of mixed perovskite in high efficiency photovoltaics

Mixed-composition perovskites (m-perovskites) are emerging as one of the hottest materials in the field of photovoltaics. However, a satisfactory m-perovskite film cannot always be attained even through a standard operating procedure. The formation of a m-perovskite film during transitory one-step spin-coating is a train of complex dynamic processes which are intimately bound up with solvent evaporation and anti-solvent interdiffusion. In these processes, many underappreciated variables that will greatly alter the mode of solvent behavior have rarely been taken into serious consideration. In this paper, the air flow velocity during spin-coating is proved to be a very important factor. A precise control over the formation as well as the decomposition of the intermediate phase can be realized through high-air-flow-velocity assisted spin-coating, which guarantees a subsequent controllable and high-quality crystallization of the m-perovskite. Finally, the planar-structured device exhibits the best efficiency of 20.24% (19.58% stabilized) with alleviated hysteresis and better long-term stability.