Bulk heterojunctions continue to be the dominant architecture for solution processed organic solar cells. In general, photoactive films on the order of 100 nm thickness have delivered the highest power conversion efficiencies. However, it is becoming increasingly apparent that thicker junctions are needed for high yield, high throughput, low cost manufacturing of commercial organic solar cells. Very few organic semiconductors are suitable for maintaining optimal efficiencies in cells with thicker junctions. This paradigm is beginning to shift with the recent high mobility donor polymers, where electrically inverted thick heterojunction structures deliver impressive efficiencies. The inverted architecture seems to be an essential feature of these solar cells. The reason for this has yet to be explained, and in this work, we address this question. We present analytical simulations and experimental evidence showing how the charge generation and extraction physics is significantly different in thin and thick heterojunctions, inverted and conventional. In particular, our predictive model shows how the inverted architecture compensates for strongly imbalanced carrier mobilities, which would otherwise cause debilitating recombination. Thick bulk heterojunctions can be designed to deliver high efficiencies, but for high mobility donors, this is only in an inverted architecture. These findings have profound implications for manufacturing of commercial organic solar cells.

Color discrimination in photodetection is conventionally achieved using broadband‐absorbing inorganic semiconductors with passive optical filters. Organic semiconductors show promise to deliver narrowband spectral responses due to their tunable optical properties. While achieving narrow‐absorbing organic semiconductors is an ongoing endeavor in the synthetic chemistry community, charge collection narrowing is introduced as a “material‐agnostic” technique to realize narrowband spectral responses using broadband absorbers such as blends of organic semiconductors, inorganic nanocrystals, and perovskites in a photodiode architecture. Charge collection narrowing in organic semiconductors demands photoactive junction thicknesses on the order of a few micrometers causing fabrication difficulties and limitations in device metrics such as frequency bandwidth. In this work it is shown that electrical inversion can result in charge collection narrowing in organic photodiodes with active layer thicknesses on the order of hundreds of nanometers and hence much easier to achieve via high throughput solution processing techniques. Additionally, it is shown that an indium tin oxide/gold electrode with modified work function acts as a cavity mirror, further narrowing the spectral response and at the same time delivering an extremely selective cathode, suppressing the dark current dramatically. Nearly voltage independent detectivities of 1013 Jones are achieved with an active sensing area of 0.2 cm2.

Achieving the highest power conversion efficiencies in bulk heterojunction organic solar cells requires a morphology that delivers electron and hole percolation pathways for optimized transport, plus sufficient donor:acceptor contact area for near unity charge transfer state formation. This is a significant structural challenge, particularly in semiconducting polymer:fullerene systems. This balancing act in the model high efficiency PTB7:PC70BM blend is studied by tuning the donor:acceptor ratio, with a view to understanding the recombination loss mechanisms above and below the fullerene transport percolation threshold. The internal quantum efficiency is found to be strongly correlated to the slower carrier mobility in agreement with other recent studies. Furthermore, second-order recombination losses dominate the shape of the current density-voltage curve in efficient blend combinations, where the fullerene phase is percolated. However, below the charge transport percolation threshold, there is an electric-field dependence of first-order losses, which includes electric-field-dependent photogeneration. In the intermediate regime, the fill factor appears to be limited by both first-and second-order losses. These findings provide additional basic understanding of the interplay between the bulk heterojunction morphology and the order of recombination in organic solar cells. They also shed light on the limitations of widely used transport models below the percolation threshold.

Single‐crystal halide perovskites exhibit photogenerated‐carriers of high mobility and long lifetime, making them excellent candidates for applications demanding thick semiconductors, such as ionizing radiation detectors, nuclear batteries, and concentrated photovoltaics. However, charge collection depreciates with increasing thickness; therefore, tens to hundreds of volts of external bias is required to extract charges from a thick perovskite layer, leading to a considerable amount of dark current and fast degradation of perovskite absorbers. However, extending the carrier‐diffusion length can mitigate many of the anticipated issues preventing the practical utilization of perovskites in the abovementioned applications. Here, single‐crystal perovskite solar cells that are up to 400 times thicker than state‐of‐the‐art perovskite polycrystalline films are fabricated, yet retain high charge‐collection efficiency in the absence of an external bias. Cells with thicknesses of 110, 214, and 290 µm display power conversion efficiencies (PCEs) of 20.0, 18.4, and 14.7%, respectively. The remarkable persistence of high PCEs, despite the increase in thickness, is a result of a long electron‐diffusion length in those cells, which was estimated, from the thickness‐dependent short‐circuit current, to be ≈0.45 mm under 1 sun illumination. These results pave the way for adapting perovskite devices to optoelectronic applications in which a thick active layer is essential.

The efficiency of tin-lead perovskite solar cells (TLPSC) has been consistently increasing. However, their photostability continues to be a persistent challenge. Besides the oxidation of tin (Sn), the presence of...