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The external radiative efficiency of a photovoltaic device is a useful metric to compare different photovoltaic technologies and material systems. However, under low‐intensity indoor lighting, a particular open‐circuit voltage dependence arises that cannot be described using the assumption of a constant external radiative efficiency, as often assumed at higher illumination intensities. As a result, the external radiative efficiency at 1 sun conditions no longer becomes a useful comparison metric for devices at indoor lighting levels. By use of absolute electroluminescence measurements of gallium arsenide photovoltaic (PV) cells, the current density dependence of the external radiative efficiency is explored and it is shown that the functional form of this dependence dictates the open‐circuit voltage losses in the low‐intensity limit. This dependence is quantified with a mathematical treatment that takes advantage of a widely accepted recombination current model in III–V photovoltaic devices, and this model is used to study the dependence of PV device open‐circuit voltage at low intensity with varying non‐radiative recombination rates. [ABSTRACT FROM AUTHOR]

A bandgap gradient at the front surface of solar absorbers can effectively suppress surface recombination while not affecting photocurrent. Herein, it is demonstrated that a front‐surface gradient can be formed in an inverted perovskite cell by introducing perovskite quantum dots (QDs) between the hole‐transporting layer (HTL) and the remaining absorber. Ultraviolet photoelectron spectroscopy reveals that, with the addition of CsPbBr3 QDs onto the HTL substrate, the subsequently deposited MAPbI3 is converted from mild p‐type to n‐type, and the resultant band alignment can effectively reduce the electron concentration at the front surface without significantly affecting hole extraction. Multiple independent characterizations further confirm the reduction of surface recombination. As a result, the inverted MAPbI3 cells exhibit an open‐circuit voltage of 1.154 V, which translates to a nonradiative recombination loss of 0.15 V and a power conversion efficiency of 20.51%. [ABSTRACT FROM AUTHOR]

The performance of thermally deposited Sb2Se3 solar cells are severely limited by various bulk and interfacial recombination, instigating a large open‐circuit voltage (VOC) deficit. Ternary Sb2(S,Se)3 is considered as a remedy, however, it is also subjected to a dilemma that improvement in VOC will be escorted by JSC loss due to the shrinkage of light harvest. Thus, a gradient of S/Se across the film is a prerequisite to avoid this detrimental compromise. Herein, the incorporation of S in the Sb2Se3 absorber layer evaporated from a CdS buffer layer during vapor transport deposition (VTD) process, and its further self‐activated diffusion at the interface upon ambient storage is explored. For the gradient indium tin oxide (ITO)/CdS/Sb2(S,Se)3/Sb2Se3/Au solar cell, the large bandgap Sb2(S,Se)3 at the heterojunction side contributes to high VOC, while the narrow bandgap Sb2Se3 at the top side confirms high JSC. Sulfur diffusion at the CdS/Sb2Se3 interface also improves the junction quality with an enlarged Vbi, reduced interfacial defects and recombination loss, thus improving VOC from 393 to 430 mV. Such VOC represents the highest value for that of thermally deposited Sb2Se3 solar cells. The champion device also delivers an interesting efficiency of 7.49%. This research provides substantial guidance in exploring efficient approaches to improve the performance of Sb2Se3 solar cells. [ABSTRACT FROM AUTHOR]

An asymmetric wide‐bandgap (WBG) nonfullerene acceptor (C6‐IDTT‐T) is developed by shearing one alkyl side‐chain from a symmetrically alkyl‐substituted indacenodithieno[3,2‐b]thiophene (IDTT) core of the fused‐ring electron acceptor 2C6‐IDTT‐T. These two acceptors both exhibit wide optical bandgaps over 1.8 eV. Investigations on the optical, electrochemical, and active layer morphology are conducted to understand the effect of asymmetric side chains on the electrical and photovoltaic properties. Compared with symmetric 2C6‐IDTT‐T, asymmetric C6‐IDTT‐T is found to exhibit redshifted absorption and higher electron mobility. As a result, the C6‐IDTT‐T blend with a thienothiophene‐benzodithiophene copolymer (PTB7‐Th) presents higher electron mobility and more balanced charge carrier transport, which leads to an enhanced power conversion efficiency of 8.51% for C6‐IDTT‐T‐based device with a high open‐circuit voltage of 1.052 V and a low energy loss of 0.60 eV. [ABSTRACT FROM AUTHOR]