Single-material organic solar cells (SMOSC) are attracted by their simple structure and ease of fabrication so that they are virtually free from a number of drawbacks of heterojunction organic solar cells. However, the performance of SMOSC is still low, first of all because of poor understanding of losses on the way of energy conversion from light to electricity. In this work, we present solution-processed SMOSC based on star-shaped π-conjugated donor-acceptor oligomers with triphenylamine donor (N-Ph₃) and alkyl- or phenyl dicyanovinyl acceptor (DCV-R) of general formulae N(Ph-nT-DCV-R)₃, where nT stands for n-oligothiophene, and study charge photogeneration and recombination in them. SMOSC demonstrate small energy losses resulting in high open-circuit voltage of 1.08–1.19 V and the power conversion efficiency up to 1.22% under illumination intensity of 0.45 sun (1.13% under one sun) with the maximum external quantum efficiency up to 24% for N(Ph-2T-DCV-Ethyl)₃, which are among the highest for SMOSC based on conjugated donor-acceptor small molecules or oligomers. It was found that monomolecular recombination dominates at the short-circuit condition and the maximum power point, but at the open-circuit condition the photoinduced charges recombine nearly bimolecularly. The bottleneck in the SMOSC performance was shown to be the field-assisted charge generation perfectly described by the Onsager model in the limit of weak electric fields. The results obtained suggest that intermolecular charge delocalization in conjugated donor-acceptor molecules would be beneficial for further progress in SMOSC.

单材料有机太阳能电池（SMOSC）因其简单的结构和易于制造而吸引，因此它们实际上没有异质结有机太阳能电池的许多缺点。但是，SMOSC的性能仍然很低，首先是因为人们对从光到电的能量转换方式中的损耗的了解不多。在这项工作中，我们介绍了基于星形π共轭给体-受体低聚物与三苯胺给体（N-Ph ₃）和烷基或苯基二氰基乙烯基受体（DCV-R）的通式N（Ph- nT-DCV-R）₃，其中nT代表n-寡聚噻吩，并研究其中的电荷光生和重组。SMOSC表现出很小的能量损耗，在1.05–1.19 V的高开路电压下，在0.45太阳的光照强度下（在一个太阳下为1.13％），功率转换效率高达1.22％，而对于N（Ph-2T-DCV-乙基）₃，这是基于共轭供体-受体小分子或低聚物的SMOSC的最高值。发现在短路条件和最大功率点时单分子复合起主导作用，但是在开路条件下光诱导的电荷几乎双分子复合。SMOSC性能的瓶颈被证明是在弱电场的限制下由Onsager模型完美描述的场辅助电荷产生。获得的结果表明，共轭的供体-受体分子中的分子间电荷离域化将有利于SMOSC的进一步发展。