wangzhaowei

Silver is a low-cost electrode material for perovskite solar cells. However, silver electrodes turn yellow after device fabrication, which is accompanied by a decrease in power conversion efficiency. These changes are caused by the formation of silver iodide from the reaction between silver and iodine-containing compounds from the perovskite layer, as demonstrated by Y. B. Qi and co-workers in article 1500195. The presence of pinholes in spiro-MeOTAD hole-transport layer facilitates silver iodide formation.

In article number 1500631, Fei Huang, Wallace C. H. Choy, and co-workers address one of the main electrical issues of the interconnecting layer (ICL) in tandem organic solar cells by introducing a dipole material to modify the counter-diode barrier between the hole transport layer (HTL) and the electron transport layer (ETL). This strategy contributes towards a general method to combine other HTL and ETL as the effective ICL.

Currently, most of the promising organic solar cells (OSCs) are based on low bandgap polymer donors with deep-lying highest occupied molecular orbit (HOMO) levels, which impose the challenges for device architecture design. In terms of fast charge extraction and suppression of bimolecular recombination, elaborate interface design in low bandgap OSCs is of significance to further boost their ultimate efficiency. In this work, a facile solution-processed functionalized single wall carbon nanotube (f-SWCNT) mesh/self-assembled molecule (SAM) hybrid structure is reported as hole transport layer (HTL) in low bandgap OSCs. The effectiveness of such hybrid HTL originates from two aspects: (i) SAM layer can effectively realize Ohmic contact between f-SWCNT and low bandgap polymer donors with deep-lying HOMO levels due to the reduction of interface energy barrier; (ii) f-SWCNT mesh can provide fast hole extraction pathways to quickly sweep out photogenerated charges. As a consequence of synergic effects of such hybrid HTL, both photocurrent and fill factor are greatly enhanced due to the reduced bimolecular recombination. Together with careful light management by using ZnO optical spacer, a high efficiency of 10.5% has been achieved. This work offers an excellent choice for large-scale processable and effective HTL toward the application in low bandgap OSCs with deep-lying energy levels.

A functionalized SWCNT mesh/self-assembled molecule (SAM) hybrid is demonstrated as a hole transport layer in polymer solar cells. The synergic effects of the f-SWCNT/SAM hybrid structure realize barrier reduction and fast charge extraction, greatly enhancing photocurrent and fill factor of low bandgap organic solar cells. Further optimizing the spatial distribution achieves a high efficiency of 10.5%.

A fundamental analysis of the external quantum efficiency (EQE) of organic tandem solar cells with equal absorbers in both subcells (homo-tandem solar cells) is presented. Providing direct access to both subcells by introducing a conductive intermediate polymer electrode into the recombination zone, without changing the optical and electric device properties, the three-terminal device becomes a proxy to the two-terminal tandem solar cell properties. From the spectrally resolved EQE of the subcells in three-terminal configuration wavelength and intensity of suitable bias light as well as bias voltage are determined that in turn allow for accurate EQE measurements of the common two-terminal tandem solar cells. Theoretic considerations allow the prediction of the tandem solar cell's EQE from its subcells' EQEs as well as the prediction of the tandem cell EQE under monochromatic bias light illumination being in excellent agreement with experimental results. All findings discussed herein can be applied to more common hetero-tandem solar cell architectures likewise.

A three-terminal tandem solar cell architecture enables detailed studies of the external quantum efficiencies (EQEs) of organic homo-tandem solar cells. Due to optoelectronic equality, all results can be transferred to conventional two-terminal tandem cells including a detailed study of subcell saturation by monochromatic bias light and bias voltage needed for accurate EQE measurements.

In article 1500118, L. Etgar and co-workers report on semi-transparent perovskite solar cells. The cell transparency is achieved through a unique wet deposition technique that creates perovskite grids with various dimensions, which enable control of the cell transparency.

Understanding the degradation and failure mechanisms of organic photovoltaic devices is a key requirement for this technology to mature toward a reliable product. Here, an investigation on accelerated temperature and moisture long-term stability testing (>20 000 h) of inverted and glass-encapsulated poly(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester solar cells is presented. The degradation kinetics is analyzed using the Arrhenius model and the resulting activation energy for the diffusion of water is measured to be ≈43 kJ mol⁻¹. Through comparison of electroluminescence imaging, lock-in thermography, and photoluminescence mapping, the device performance is correlated with the loss of effective cell area and it is shown that the reaction of water at the hole extraction/active layer interface is likely to be the dominant cause for long-term device failure. The diffusion of water through the packaged solar cell is described using classical diffusion theory. Based on an analytical solution of a simple diffusion model, the diffusion coefficient is estimated to be 4 × 10⁻¹² m² s⁻¹. A shelf life of 100 000 h is anticipated at 65 °C/85% RH using a 9.3 cm wide protective adhesive rim. The findings of this study may inform strategies for predicting lifetimes of organic solar cells and modules based on local in situ tracking of moisture-induced device performance loss using IR imaging.

Lifetime limitations of current-generation inverted and encapsulated organic solar cells under damp heat conditions are identified by correlating photovoltaic device performance with lock-in IR imaging techniques. The combination of electroluminescence imaging and water diffusion modeling may inform strategies for predicting early performance losses in solar cells and modules.

Continuous illumination of the organometal trihalide perovskite (OTP) devices can cause the photovoltaic poling effect, termed light-induced self-poling (LISP), which improves the stabilized device efficiency significantly. The effect of LISP is comparable to the poling by an externally applied electric field, which can be explained by the redistribution of ions/vacancies within the OTP layers driven by a photovoltage-induced additional electric field.