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Two-terminal tandem perovskite (PK) cells are considered a promising option for future photovoltaic (PV) market due to the rapid improvements in their power conversion efficiencies. However, their large-scale adoption requires a better understanding on the energy performance of these PVs. In this paper, the life-cycle energy consumptions of two-terminal tandem solar cells consisting of lead-based PK top cells prepared on bottom cells of copper indium gallium selenide, copper zinc tin selenide, and monocrystalline silicon are evaluated. The energy payback time (EPBT) and the energy return on invested (EROI) are the two useful metrics for examining the energy generation performance of PV systems. EPBTs of the current state-of-the-art devices range from 7 months to 12 months, while the EROI of the cells is in the reverse order as the EPBT and ranged between 5.2 and 9.2. These two energy indicators of tandem devices are expected to improve as the tandem PV technologies mature, with an EBPT as low as ∼27 day (0.9 month) and the EROI as high as 105 for high-efficiency long-lifetime devices.

Optically transparent p-type materials play a critical role in transparent electronics including photovoltaic (PV) devices. P-type sulfide materials offer an alternative to oxides for PV application due to improved hole transport properties. Here, we report the solution-based synthesis of earth-abundant p-type transparent conducting barium copper sulfide (α-BaCu4S3, BCS) thin films. These films were characterized using scanning electron microscopy, X-ray diffraction, UV–Vis–NIR spectrophotometry, Raman spectroscopy, and spectroscopic ellipsometry. BCS films of ~100 nm thickness transmit >70% of visible light. We report on tests of the hole transport properties of these BCS films for cadmium telluride (CdTe) photovoltaics, finding that the BCS deposition process forms a beneficial tellurium (Te) rich surface on CdTe by selectively removing Cd from the surface. Based on our study, the BCS interface layer plays dual functions for CdTe PV devices as a hole transport material and as an etchant, enhancing the resulting device performance. We observed a significant increase in open-circuit voltage of CdTe solar cells with the BCS buffer layer. Additionally, we discuss semitransparent CdTe solar cells with BCS as a hole transport layer and indium tin oxide as a finishing electrode. Semitransparent CdTe solar cells shows 13.3% conversion efficiency for the front side illumination and 1.2% efficiency for back side illumination, indicating high recombination of charge carriers generated close to the rear CdTe/BCS/ITO contact.

Carbon single wall nanotube (SWNT) films were applied as electrodes to replace the p-layer in hydrogenated amorphous silicon (a-Si:H) solar cells. Devices were fabricated by transferring vacuum-filtered SWNT films of varying thickness onto a-Si:H layers grown by plasma enhance chemical vapor deposition on Pilkington TEC 15 glass substrates. Cells incorporating SWNTs were illuminated from each side (glass / SWNT). A cell illuminated through a 25 nm thick SWNT film yielded short circuit current density, open circuit voltage, and efficiency of 5.47 mA/cm2, 0.793 V, and 1.46%, respectively. Maximum quantum efficiency of 48% was measured at 475 nm for the same device.