wangzhaowei

To achieve high performance for inverted structure perovskite solar cells, the design of hole-transporting layer (HTL) and related interfacial engineering are very important tasks. To avoid the hygroscopic characteristics of poly (3, 4-ethylenedioxythiophene):poly (styrenesulfonate) that may degrade the adjacent moisture-sensitive perovskite layer, here, a new CrO_x-based hole-transport material has been introduced. The feasibility of fabrication efficient perovskite solar cells with CrO_x and Cu-CrO_x as HTLs is confirmed for the first time. Cu doping can modify the chromium ion contents and suppress the formation of surface hydroxylation and CrO₃ in the CrO_x film, which can increase work function, electrical conductivity, and carrier mobility of the CrO_x films. Consequently, the power conversion efficiency of the corresponding device increases to 10.99% from its original value of 9.27%. This study not only provides a novel HTL system for high performance and decently stable optoelectronic devices but also reveals the importance of HTL doping for interface engineering.

A new CrO_x-based hole-transport layer is deposited by reactive cosputtering of Cr and Cu from a composite target. With Cu doping, CrO₃ and CrO(OH)/Cr(OH)₃ in CrO_x film are suppressed to avoid reacting with the degradation product of CH₃NH₃PbI₃. Consequently, the power conversion efficiency of the device increases to 10.99% from its original 9.27%.

A series of simple alkylated triphenylamine molecules are designed and synthesized as hole transporting materials (HTMs) for perovskite solar cells. The effects of the alkyl chains on the photovoltaic performance are for the first time systematically investigated. A high efficiency of 17.33% is achieved by combining HTM X21 and the mixed-ion perovskites.

Organic solar cells based on two benzodithiophene-based polymers (PTB7 and PTB7-Th) processed at square centimeter-size under inert atmosphere and ambient air, respectively, are investigated. It is demonstrated that the performance of solar cells processed under inert atmosphere is not limited by the upscaling of photoactive layer and the interfacial layers. Thorough morphological and electrical characterizations of optimized layers and corresponding devices reveal that performance losses due to area enlargement are only caused by the sheet resistance of the transparent electrode reducing the efficiency from 9.3% of 7.8% for PTB7-Th in the condition that both photoactive layer and the interfacial layers are of high layer quality. Air processing of photoactive layer and the interfacial layers into centimeter-sized solar cells lead to additional, but only slight, losses (<10%) in all photovoltaic parameters, which can be addressed to changes in the electronic properties of both active layer and ZnO layers rather than changes in layer morphology. The demonstrated compatibility of polymer solar cells using solution-processed photoactive layer and interfacial layers with large area indicates that the introduction of a standard active area of 1 cm² for measuring efficiency of organic record solar cells is feasible. However electric standards for indium tin oxides (ITO) or alternative transparent electrodes need to be developed so that performance of new photovoltaic materials can be compared at square centimeter-size.

Increasing solar cells based on benzo-dithiophene-based polymers (PTB7 and PTB7-Th) to square-centimeter size leads to performance losses that are not caused by the area enlargement of the photoactive and interlayer, respectively, but are only related to the sheet resistance of the transparent electrode based on indium tin oxide. Air processing generates an additional but small loss in efficiency (<10%) due to changes of the electronic properties of each layer.

Layer-by-layer (LL) processes, i.e., sequential deposition of different active layers, are widely used in the fabrication of organic solar cells (OSCs). Recently, LL vacuum deposition and LL solution processes have attracted considerable attention. LL processing presents some advantages over the blend method: a) donor and acceptor layers can be easily and independently controlled and optimized; b) the charge carriers dissociated from excitons at the donor–acceptor interface are confined to each phase, so bimolecular recombination losses can be reduced; c) bilayer geometries enable an easier way for understanding the physical processes taking place at the donor–acceptor interface; d) desired vertical phase separation for charge extraction can be obtained through changing the sequence of donor and acceptor deposition. This report summarizes the recent developments of LL processed OSCs. The remaining problems and challenges, and the key research direction in near future are discussed.

Layer-by-layer (LL) processing techniques exhibit some advantages over the traditional blend-casting technique in organic solar cells. The recent developments of LL vacuum-deposited and solution-processed solar cells are summarized.

The rapid degradation of organic photovoltaic (OPV) devices compared to conventional inorganic solar cells is one of the critical issues that have to be solved in order to make OPV a competitive commercial technology. The understanding of the fundamental mechanisms that reduce the power conversion efficiency (PCE) over time is beneficial for the design of new materials with enhanced stability. This paper focuses on bulk heterojunction organic solar cells based on thieno [3,4-b] thiophene-alt-benzodithiophene (PTB7) mixed with [6,6]-phenyl-C71-butyric acid methyl esther ([70]PCBM). In spite of being promising in terms of PCE, devices based on this blend are unstable and have a short lifetime. When exposed to light in inert atmosphere, the PCE drops by 15% in less than 1 h and by 35% in 8 h; this degradation is induced by the ultraviolet (UV) part of the spectrum. This paper analyzes the effect induced by UV light on the transport of charges in PTB7:[70]PCBM. Contrary to expectations, the electron transport shows evidence of trapping, while the transport of holes appears unaffected. Furthermore, it is proven that the loss of PCE is due to a reaction between PTB7 and [70]PCBM, while the intrinsic instability of the polymer plays a marginal role.

The effect of UV light on the charge transport in PTB7:[70]PCBM solar cells is investigated; while the hole transport is stable, a deterioration in the transport of electrons is found, related to the increased electron trapping. It is proven that efficiency losses of PTB7:[70]PCBM solar cells upon UV exposure are due to a reaction that involves both the donor and the acceptor.

The rapid pace of development for hybrid perovskite photovoltaics has recently resulted in promising figures of merit being obtained with regard to device stability. Rather than relying upon expensive barrier materials, realizing market-competitive lifetimes is likely to require the development of intrinsically stable devices, and to this end accelerated aging tests can help identify degradation mechanisms that arise over the long term. Here, oxygen-induced degradation of archetypal perovskite solar cells under operation is observed, even in dry conditions. With prolonged aging, this process ultimately drives decomposition of the perovskite. It is deduced that this is related to charge build-up in the perovskite layer, and it is shown that by efficiently extracting charge this degradation can be mitigated. The results confirm the importance of high charge-extraction efficiency in maximizing the tolerance of perovskite solar cells to oxygen.

Key to the development of perovskite photovoltaics is the mitigation of long-term degradation mechanisms. When aging these solar cells in the presence of oxygen, two stages of degradation are evidenced that drive perovskite decomposition. This damage is coupled to the average density of charge within the perovskite, highlighting the need to maximize charge extraction efficiency when designing stable devices.

On-fabrication solid-state N-doping of graphene is developed using a Zonyl-added ZnO layer on a graphene surface. Inverted organic solar cells based on the graphene cathode and the ZnO layer exhibit a power conversion efficiency of 7.5%—a high-record power conversion efficiency of single-junction organic solar cells with graphene electrodes. For the first time 100% power conversion efficiency with respect to the ITO cathode is achieved.

Periodic nanocone-nanopillar dual-structured arrays are wet chemical etched on 20 μm-thick crystalline silicon substrates by Pingqi Gao, Xiaofeng Li, Jichun Ye and co-workers in article number 1501793. This structure enables the realization of excellent light absorption properties and enhanced electrical contact with PEDOT:PSS. The final textured silicon/PEDOT:PSS thin film hybrid solar cell shows a power conversion efficiency of 12.2%.