Indoor photovoltaics (IPVs) harvest ambient light to produce electricity and can cleanly power the rapidly growing number of Internet-of-Things (IoT) sensors. The surge in IPV development, with new proposed materials, devices and products, creates the need to critically evaluate how IPV devices have advanced and to assess their prospects. In this Review, we analyse the status, challenges and opportunities of established and emerging IPV technologies, including metal-halide perovskite, organic photovoltaics, dye-sensitized solar cell and perovskite-inspired materials. Many emerging low-toxicity semiconductor materials could reach IPV efficiencies of up to 50%, but carrier localization and defect trapping hinder their performance. Wide adoption of standardized performance assessment methods is essential, and further harmonization is needed for stress tests, qualification standards and energy rating assessments. For seamless IPV integration in IoT devices, series-connected cell modules and appropriate power management hardware are crucial to maximize energy extraction. IPV device stability, technology upscaling and cost-effective integration in IoT sensors must be further developed but balanced with sustainability across the entire value chain.

Photovoltaics (PVs) are a critical technology for curbing growing levels of anthropogenic greenhouse gas emissions, and meeting increases in future demand for low-carbon electricity. In order to fulfill ambitions for net-zero carbon dioxide equivalent (CO₂eq) emissions worldwide, the global cumulative capacity of solar PVs must increase by an order of magnitude from 0.9 TW_p in 2021 to 8.5 TW_p by 2050 according to the International Renewable Energy Agency, which is considered to be a highly conservative estimate. In 2020, the Henry Royce Institute brought together the UK PV community to discuss the critical technological and infrastructure challenges that need to be overcome to address the vast challenges in accelerating PV deployment. Herein, we examine the key developments in the global community, especially the progress made in the field since this earlier roadmap, bringing together experts primarily from the UK across the breadth of the PVs community. The focus is both on the challenges in improving the efficiency, stability and levelized cost of electricity of current technologies for utility-scale PVs, as well as the fundamental questions in novel technologies that can have a significant impact on emerging markets, such as indoor PVs, space PVs, and agrivoltaics. We discuss challenges in advanced metrology and computational tools, as well as the growing synergies between PVs and solar fuels, and offer a perspective on the environmental sustainability of the PV industry. Through this roadmap, we emphasize promising pathways forward in both the short- and long-term, and for communities working on technologies across a range of maturity levels to learn from each other.

There is an increasing interest in using indoor photovoltaic (IPV) devices to power Internet of Things applications, low power communications, and indoor environmental sensing. For the commercialization of IPV technologies, device performance measurements need to conform to the relevant standardized specifications. We present a novel IPV device measurement system that incorporates digital light processing (DLP) to deliver a spectrally invariant light source at all required illuminance levels, as specified by the indoor standard testing conditions in IEC TS 62607-7-2:2023. We evaluated the DLP system according to requirements for spectral coincidence, temporal stability, and non-uniformity at the sample plane. We demonstrate the measurements to define the classification status of the system and the unique benefits of the DLP system that allow a stable spectral profile and high levels of uniformity across all illuminance levels. This is the first reported measurement system for IPV device testing based on DLP technology, and the classification methodology of this work can be used as an example for the classification of indoor light simulators in laboratory environments based on the latest IEC TS 62607-7-2:2023.

Understanding the performance and aging mechanisms in photovoltaic devices requires a spatial assessment of the device properties. The current dominant technique, electroluminescence, has the disadvantage that it assesses radiative recombination only. A complementary method, laser beam-induced current (LBIC), is too slow for high-throughput measurements. This paper presents the description, design, and proof of concept of a new measurement method to significantly accelerate LBIC measurements. The method allows mapping of the current response map of solar cells and modules at drastically reduced acquisition times. This acceleration is achieved by projecting a number of mathematically derived patterns on the sample by using a digital micromirror device (DMD). The spatially resolved signal is then recovered using compressed sensing techniques. The system has fewer moving parts and is demonstrated to require fewer overall measurements. Compared with conventional LBIC imaging using galvanic mirror arrangements or xy scanners, the use of a DMD allows a significantly faster and more repeatable illumination of the device under test. In this proof-of-concept instrument, sampling patterns are drawn from Walsh-Hadamard matrices, which are one of the many operators that can be used to realize this technique. This has the advantage of the signal-to-noise ratio of the measurement being significantly increased and thus allows elimination of the standard lock-in techniques for signal detection, reducing measurement costs, and increasing measurement speed further. This new method has the potential to substantially decrease the time taken for measurement, which demonstrates a dramatic improvement in the utility of LBIC instrumentation.

A new photovoltaic (PV) device current mapping method has been developed, combining the recently introduced compressed sensing (CS) sampling theory with light beam induced current (LBIC) measurements. Instead of a raster scan, compressive sampling is applied using a digital micromirror device. The aim is to significantly reduce the time required to produce a current map, compared to conventional LBIC measurements. This is achieved by acquiring fewer measurements than a full raster scan and by utilizing the fast response of the micromirror device to modulate measurement conditions. The method has been implemented on an optical current mapping setup built at the National Physical Laboratory, U.K. Measurements with two different PV cells are presented in this paper and an analytical description for realization of an optimized CS current mapping system is provided. The experimental results illustrate the feasibility of the method and its potential to significantly reduce measurement time of current mapping of PV devices.