• Energy Research

Abstract Organic solar cells are ideal for semi-transparent applications given their “peaky” absorption, which allows them to selectively absorb photons outside the visible range while transmitting visible light. Such devices embody a fundamental tradeoff between transparency and power generation that must be optimized to fit the requirements of each potential application—for example, powering electrically dimmable smart windows. To inform the design of organic ultraviolet-absorbers and solar cells that target such applications, we computer-generate sets of optical constants with a range of absorption coefficients and absorption cutoff wavelengths that mimic those of real organic semiconductors. We then perform optical transfer-matrix simulations to determine the absorption and transmission spectra of full-stack photovoltaic cells, inserting these computer-generated optical constants to describe the photoactive absorbing layers. We find that solar cells having absorbers with a cutoff wavelength of 420 nm produce the most power without degrading transparency or color neutrality, and that absorption coefficients up to 5 × 105 cm−1 are needed to fully absorb the targeted wavelengths within practical photoactive layer thicknesses

AbstractImproving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.

Perovskite CsPbI3 is a promising photovoltaic absorber material, thanks to its ideal bandgap for Si-tandem solar cell applications and its excellent thermochemical stability compared with hybrid organic–inorganic perovskites. However, CsPbI3 has its own stability challenges as its photoactive β- and γ-polymorphs are thermodynamically unstable at room temperature compared with the yellow non-perovskite δ-phase. Stabilizing CsPbI3 has, thus, been the subject of considerable research in recent years. While some approaches, such as alloying with halides and reducing crystalline domain size, have proven effective in improving phase stability, these benefits have, thus far, come at the expense of photovoltaic efficiency compared with the state-of-the-art CsPbI3 solar cells. In this perspective, we discuss the progress and limitations of inorganic perovskite stabilization techniques and look forward at how to achieve inorganic perovskite solar cells with both commercially viable efficiencies and lifetimes.

Using a combination of Fourier transform infrared (FTIR) spectroscopy and physics-based degradation models, we find that the early aging of small molecular weight organic photovoltaic (OPV) cells is due to photochemical degradation of the C60acceptor layer.

Voltage-dependent characterizations of organic solar cells with brightly-emitting charge-transfer excitons reveal excitation dynamics and trends as a function of donor molecule.

Abstract We investigate the photostability of organic photovoltaic (OPV) cell active layers comprised of the archetype donor, boron-subphthalocyanine chloride (SubPc), and fullerene acceptors, aged under either AM1.5G illumination or in the dark, and in either air or inert atmosphere. Under long-term exposure to light, we observe significant photobleaching and crystallization of SubPc. Mixing SubPc with C 60 as is commonly done in high efficiency small molecule OPVs, the crystallite formation is inhibited and the bleaching is suppressed due to a significantly reduced exciton lifetime in the blends. Furthermore, the spectral dependence of the degradation suggests that photo-dimerization of C 60 is an important factor leading to burn-in loss in efficiency previously reported in SubPc/C 60 OPVs. The existence of dimerization is supported by Fourier transform infrared spectroscopy data taken both before and after exposure to light. Increasing the fraction of SubPc in a SubPc:C 60 blend leads to a decrease in the rate of film degradation, providing further evidence for C 60 dimerization. Due to its reduced tendency for photo-dimerization, C 70 is more stable than C 60 when used in small molecule OPVs.

The power conversion efficiency of organic solar cells has rapidly increased, yet significantly less attention has been paid to materials stability and device longevity. For organic solar cells to make an impact in the marketplace, researchers, funding agencies and journals should do more to address this crucial gap.